Comparative Study on Phacoemulsification Techniques and Intraocular Lens Implantation in Dogs with Cataract

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Cataracts are a leading cause of vision loss in dogs, significantly affecting quality of life. Surgical removal via phacoemulsification with intraocular lens (IOL)implantation is the only effective treatment. This study compared monomanual and bimanual phacoemulsification, as well as two foldable acrylic IOL types, in 60 dogs (120 eyes). Postoperative vision was assessed using standard tests and a custom visual scoring scale. Both techniques restored vision effectively, with faster recovery and fewer complications for bimanual phaco in mature cataracts and monomanual phaco in intumescent cataracts. The study highlights the importance of choosing the optimal surgical approach and IOL type for best outcomes.

Abstract

Cataracts are one of the leading causes of vision loss in dogs, significantly impairing their quality of life and visual behavior. Phacoemulsification, followed by intraocular lens (IOL) implantation, is currently the gold standard for visual rehabilitation. This non-randomized clinical study included 60 dogs (120 eyes)of various breeds, ages, and sizes, diagnosed with cataracts of different etiologies and degrees of evolution (incipient, mature, hypermature, and intumescent). Postoperative visual function was assessed using conventional neuro-ophthalmologic tests (menace response, cotton ball test, maze navigation) and a custom-designed visual scoring scale developed by the authors to objectively quantify functional recovery. The bimanual technique (Phaco 2) showed slightly shorter surgical times than the monomanual approach (Phaco 1), with significant differences during the capsulorhexis (T1) and IOL implantation (T4) phases (p < 0.05). Postoperative inflammation was mild and transient, with no IOL decentration or posterior capsule opacification observed over 60 days. Visual function improved progressively, with 79.2% (95/120 eyes) reaching functional vision by two months and mean recovery exceeding 90%of normal by day 30. Both techniques provided favorable short-term outcomes for canine cataract extraction, with outcomes mainly influenced by cataract type and lens consistency. The proposed visual scoring system represents a preliminary clinical tool that may support standardized evaluation of postoperative vision in dogs. The results highlight the importance of ongoing refinement in surgical training and the standardization of phacoemulsification protocols to improve reproducibility and long-term outcomes in veterinary ophthalmology.

1. Introduction

Cataracts represent one of the most frequent causes of visual impairment and blindness in dogs and constitute a major concern in veterinary ophthalmology due to their high prevalence and impact on animal welfare. The condition is defined as any loss of transparency of the crystalline lens, regardless of etiology or stage, and may develop secondary to hereditary, metabolic, traumatic, or age-related factors. Although medical management may temporarily delay lens opacification, surgical removal of the cataract remains the only effective therapeutic option to restore vision.

Phacoemulsification has become the gold standard procedure for cataract extraction in both human and veterinary ophthalmology [1,2,3,4,5,6,7]. The technique allows emulsification and aspiration of the opacified lens through a small corneal incision, followed by intraocular lens (IOL) implantation to restore emmetropia. Despite being minimally invasive, phacoemulsification in dogs is technically demanding because of species-specific ocular anatomy, variations in anterior chamber depth, and lens hardness that differ with cataract maturity.

Two major approaches are used in canine cataract surgery: monomanual and bimanual phacoemulsification. The monomanual technique employs a single main incision through which both irrigation and aspiration are performed, whereas the bimanual technique uses two separate instruments for greater control of lens fragments and improved anterior chamber stability. Several reports suggest that surgical outcomes are influenced by cataract consistency, surgical time, and intraoperative complications, but comparative data between the two techniques remain limited in veterinary literature. Existing studies have mainly focused on small clinical series or experimental models, providing limited quantitative evidence on technique-dependent outcomes or intraocular lens performance in dogs. Therefore, there is a clear need for structured clinical comparisons addressing both phacoemulsification technique and IOL type within the same patient population.

Intraocular lens implantation is essential for restoring normal visual function after lens extraction. Foldable acrylic IOLs are currently preferred due to their high biocompatibility, optical quality, and ability to be implanted through small incisions. However, differences in lens design and haptic configuration may affect postoperative stability and visual quality.

The present study aimed to perform a comparative clinical evaluation of monomanual and bimanual phacoemulsification techniques and to assess the short-term postoperative results of two foldable acrylic intraocular lenses used in canine cataract surgery. The objectives were to analyze the influence of cataract type, maturity, and intraoperative parameters on surgical time and postoperative recovery and to validate a visual scoring system developed by the authors for quantitative assessment of postoperative visual function in dogs. It was hypothesized that the bimanual technique would provide enhanced anterior chamber stability and more controlled nucleus fragmentation in mature or hypermature cataracts, while the monomanual approach would remain efficient and time-saving in immature lenses with preserved capsular integrity.

2. Materials and Methods

2.1. Animals and Study Design

The study population was selected from dogs of the SC Mobovet SRL Veterinary Clinic in Satu Mare, Romania, a referral veterinary clinic from northwest Romania, all of which had been previously diagnosed with cataract. Inclusion was based on a written consent form signed by each dog owner. The biological material used in this study consisted of dogs (Canis familiaris). The animal cohort included both mixed-breed dogs and purebred individuals, as well as crossbreeds resulting from various genetic combinations. Both males and females were included, with some being neutered while others remained intact. This diversity was intentionally maintained to closely reflect the general canine population commonly encountered in veterinary clinical practice. A total of 60 dogs (120 eyes)were included in the study, each undergoing bilateral cataract surgery, resulting in 120 procedures. The dogs were assigned to four experimental groups (L1–L4;

Table 1. Experimental design and grouping of dogs included in the study (n =6 0 dogs, 120 eyes).

Group	No. of Dogs	Cataract Type/Stage	Visual Status (Pre-Surgery)	Right Eye (OD)	Left Eye (OS)	Phaco-Emulsification Technique	IOL Model(s)	Experimental Purpose
L1 (Group 1)	15	Immature/Intumescent	Partial vision loss in both eyes	IOL1 implanted	IOL2 implanted	Phaco 1 (both eyes)	IOL1 (OD), IOL2 (OS)	Compare IOL models under same phaco technique in partially sighted dogs
L2 (Group 2)	15	Mature/Hypermature	Total vision loss in both eyes	IOL1 implanted	IOL2 implanted	Phaco 1 (both eyes)	IOL1 (OD), IOL2 (OS)	Compare IOL models under same phaco technique in blind dogs
L3 (Group 3)	15	Immature	Partial vision loss	Phaco 1 + IOL1	Phaco 2 + IOL1	Phaco 1 (OD) vs. Phaco 2 (OS)	IOL1 (both eyes)	Compare surgical techniques in same dog (immature cataract)
L4 (Group 4)	15	Mature/Hypermature	Total vision loss	Phaco 1 + IOL1	Phaco 2 + IOL1	Phaco 1 (OD) vs. Phaco 2 (OS)	IOL1 (both eyes)	Compare surgical techniques in same dog (mature cataract)

Notes: Each dog underwent bilateral cataract surgery (120 surgeries total). Recorded parameters per dog included: age, body size (1–3), body weight (kg), sex (F/M), neuter status (Y/N), cataract stage, and previous ocular disease. Experiment 1: Groups 3 and 4→comparison of phacoemulsification techniques (Phaco 1 vs. Phaco 2). Experiment 2: Groups 1 and 2→ comparison of IOL models (IOL1 vs. IOL2).

) based on three criteria: cataract type (intumescent, mature, or hypermature), phacoemulsification technique (two methods), and intraocular lens (IOL) model (two foldable acrylic lenses). For each dog (Table S1), detailed parameters were recorded, including age, body size (coded: small—1, medium—2, large—3), body weight, sex (F/M), neutering status, cataract stage (immature, mature, hypermature), and history of previous ocular diseases (Yes/No, with details if present). Dogs assigned to Groups 1 and 2 were selected based on the presence of the same stage of cataract evolution and equivalent visual function in both eyes. In contrast, dogs included in Groups 3 and 4 presented different stages of cataract progression and varying degrees of blindness between the two eyes (see Supplementary Materials Table S1).

2.2. Ethical Approval

All surgical procedures were performed as part of therapeutic clinical care for privately owned dogs presented with cataracts, and no experimental interventions were conducted. Written informed consent was obtained from each owner prior to surgery. The study was a retrospective analysis of clinical outcomes, conducted in accordance with national veterinary legislation as part of a PhD study program, and approved by the Institutional Ethical Committee under Ethical Statement No. 03, dated 10 November 2021.

2.3. Surgical Equipment and Instruments

All surgical procedures were performed using fully prepared ophthalmic and microsurgical instruments. A Carl Zeiss operating microscope (Carl Zeiss AG, Oberkochen, Germany) with adjustable magnification, inclinable binoculars, wide-field view, and LED illumination provided optimal visualization and maneuverability. Both phacoemulsification techniques utilized a Stellaris ultrasonic unit (Bausch & Lomb, Rochester, NY, USA), and corneal incisions were made with single-use 1.2 mm and 2.2 mm ophthalmic blades (An-Vision GmbH, Hennigsdorf, Germany).

2.4. Types of Intraocular Lenses (IOLs)

Advances in intraocular lens (IOL) materials have significantly improved optical performance and reduced postoperative complications. Modern IOLs offer high biocompatibility, UV protection, a 360° posterior barrier to delay capsular opacification, haptics with peripheral fixation holes to prevent vaulting, extended depth of focus, and foldable acrylic design for implantation through small self-sealing incisions. This study used two foldable acrylic IOL models, Fo-X and MD4 (An-Vision GmbH, Hennigsdorf, Germany), selected for their advanced optical and structural features suitable for capsular-bag implantation.

2.5. Intraocular Lens Characteristics

The study used two veterinary-specific IOL models, Fo-X and MD4 (An-Vision GmbH, Hennigsdorf, Germany), both made of hydrophilic acrylic with a hydrophobic surface (25%water) for easy folding and reduced risk of posterior capsular opacification (PCO). Square-edged haptics provide capsular stability and minimize lens displacement. The Fo-X is the company’s first canine-specific monofocal lens (D +41.0) with extended depth of focus, offering improved optical correction for myopic, hypermetropic, and near vision in emmetropic dogs. The MD4 features a thin, lightweight optical profile, with fewer size options than Fo-X. Lens size was chosen based on body size: 10–12 for small, 13 for medium, and 14 for large breeds.

2.6. Medications and Substances Used

Preoperative care began three days before surgery with topical gentamicin-dexamethasone drops (Gentocin Ophthalmic Plus, Romvac SA, Voluntari, Romania) twice daily and systemic robenacoxib (Onsior^®, Elaco, Indianapolis, IN, USA, 1 mg/kg once daily). Dogs with lens-induced uveitis received daily systemic dexamethasone 0.2%injections (Dexaveto^®, V.M.D.n.v. Arendonk, Belgium) until inflammation was resolved. Thirty minutes before surgery, tropicamide 0.5% drops (Tropicamide RPH^®, Rompharm Company, Otopeni, Romania) were applied every five minutes to induce mydriasis.

Postoperatively, both topical and systemic treatments continued. Topical anti-inflammatory and antibiotic drops were administered 4–6 times daily, tapering to 1–2 times per day over 3–4 weeks. Anti-glaucoma drops (dorzolamide 2% or timolol 0.5%)were added if intra-ocular pressure (IOP) exceeded 25 mmHg. Systemic robenacoxib continued for two weeks, with antibiotics used if infection was suspected.

2.7. Internal Medicine and Ophthalmological Exams

Dogs diagnosed with cataracts were initially screened to exclude those with major systemic diseases such as diabetes or cardiac disorders. Remaining candidates underwent hematological and biochemical testing using a Melet Schloesing MS-4s VET hematology analyzer (Melet Schloesing Laboratories GmbH, Osny, France) and a Mindray Vetube 30 biochemical analyzer (Mindray Animal Medical Technology Co., Ltd., Shenzhen, China), assessing parameters including TP, ALB, GLOB, ALT, AST, ALP, CK, α-AMY, BUN, CREA, Ca, P, TC, and GLU. Dogs with significant deviations were excluded. All selected dogs underwent a complete ophthalmologic examination, including direct ophthalmoscopy, slit-lamp biomicroscopy, and indirect ophthalmoscopy. Fundus evaluation was attempted when possible; for eyes with dense, mature, or hypermature cataracts, ocular ultrasonography assessed retinal and vitreous integrity. Dogs with retinal degeneration, detachment, or other structural ocular abnormalities unrelated to cataract were excluded.

Anterior Segment Evaluation and Ocular Integrity. Anterior segment integrity was assessed using fluorescein staining to check corneal health, Schirmer tear test (STT-1)to evaluate tear production, and slit-lamp biomicroscopy to examine corneal transparency, anterior chamber depth, and pupillary symmetry. Lens position and zonular stability were evaluated via retroillumination. When lens opacity prevented posterior segment visualization, B-scan ultrasonography confirmed retinal attachment and vitreous homogeneity. These assessments provided ocular health and anatomical integrity before surgery, minimizing postoperative complications and standardizing baseline conditions for all subjects [8].

Tonometry and Visual function Testing. Intraocular pressure was measured with a TonoVet rebound tonometer, and dogs with elevated IOP were excluded to avoid confounding by glaucoma or ocular hypertension. Visual function was assessed alongside owner observations: dogs with immature cataracts showed partial impairment, while those with mature or hypermature cataracts were completely blind. Dogs with incipient cataracts were excluded, as functional vision was adequate and surgery was not clinically indicated [8].

2.8. Anesthetic Protocol

Surgery was performed under general anesthesia, including premedication, induction, and maintenance. Premedication consisted of either diazepam (0.5–1 mg/kg IV)with ketamine (8 mg/kg IM)or medetomidine (10 µg/kg IM)with butorphanol (0.2 mg/kg IM). Anesthesia was induced with propofol (3–6 mg/kg IV)to effect. After intubation, dogs were connected to a closed-circuit system with assisted ventilation, and anesthesia was maintained with isoflurane (0.5–5%)in oxygen via intermittent positive-pressure ventilation.

2.9. Surgical Techniques and Operative Phases

Cataract surgery in all groups was performed via extracapsular extraction using endocapsular phacoemulsification, the standard in veterinary ophthalmology [1,2,3,4,5,6,7,9]. Two techniques were applied: Phaco 1 (monomanual), using a single probe for fragmentation, emulsification, and aspiration, and Phaco 2 (bimanual), using a main probe with two additional microinstruments for cortical aspiration and posterior capsule polishing. Procedures were divided into four operative phases: T1—corneal incision to capsulorhexis; T2—lens nucleus emulsification to cortical removal; T3—aspiration of residual capsular material; T4—IOL implantation (Figure 1). Each phase was scored by duration: 1 (<3 min), 2 (4–5 min), 3 (5–10 min), 4 (10–20 min), 5 (>20 min).

Method 1 of Phacoemulsification—Phaco 1. The Phaco 1 technique, a standard one-hand phacoemulsification, was applied to eyes with immature cataracts (Groups L1 and L3) and mature or hypermature cataracts (Group L4).

T1: A single 2.8 mm corneal incision was made at a 15° angle to the sclera, followed by anterior capsule staining with trypan blue and anterior chamber stabilization with viscoelastic. Continuous curvilinear capsulorhexis was performed using Utrata forceps. Duration was recorded and scored 1–5.

T2: Hydrodissection, lens rotation, and nucleus phacoemulsification were performed using standardized parameters (60% power, 40 cc/min aspiration, 12 pulses/s). The phaco-chop technique was adapted to nucleus density; cases requiring increased power or vacuum were labeled “Phaco-Chop Modified.”

T3: Cortical remnants were aspirated using irrigation/aspiration mode, and the anterior capsule was polished for a minimum of one minute.

T4: The intraocular lens (IOL MD4 or IOL1/2)was implanted in the capsular bag, sized appropriately per dog. Viscoelastic was removed, an air bubble was injected, and the corneal incision was closed with 8-0 mononylon sutures.

Phacoemulsification Method 2—Phaco 2. The Phaco 2 technique, a two-handed approach, was applied to Group L2 and the left eye (OS) of Groups L3 and L4.

T1: A main 2.4–3.0 mm corneal incision was made at the limbus, with two additional 1.2 mm paracenteses for auxiliary instruments. Trypan blue stained the anterior capsule, and viscoelastic stabilized the chamber. Continuous curvilinear capsulorhexis was performed through the main incision, while auxiliary incisions facilitated nucleus and cortical manipulation. Duration was recorded and scored.

T2: Lens emulsification and aspiration were performed via the main probe, with cortical aspiration in bimanual configuration. Standard phaco parameters (60% power, 40 cc/min, 12 pulses/s) were used; denser nuclei requiring increased power or vacuum were noted as “Phaco-Chop Modified.”

T3: Residual cortical material was aspirated and the anterior capsule was polished for at least one minute.

T4: A thin Fo-X Canine IOL, sized to the dog, was implanted in the capsular bag for all relevant eyes.

2.10. Intraocular Lens Implantation

Sterile, preloaded IOLs were implanted through the main corneal incision into the capsular bag after lens removal, with implantation time recorded for each case. Post-implantation, viscoelastic was aspirated, a small air bubble was injected to stabilize the anterior chamber, and corneal incisions were hydrated. The main incision was closed with 8-0 mononylon sutures, while secondary incisions were self-sealing or secured with a single suture if needed.

2.11. Post-Surgical Care

Postoperative management is critical for long-term visual outcomes. Dogs stayed hospitalized for two nights (pre-and post-surgery) and were discharged with care instructions: protective Elizabethan collars were worn continuously for two weeks; physical activity was limited to short, calm leash walks, gradually increasing in weeks three and four, while vigorous movements were prohibited; harnesses were recommended to avoid neck pressure; and all prescribed topical and systemic medications were to be administered as directed.

2.12. Postsurgical Control and Follow-Up

Follow-up examinations were conducted to monitor ocular health and detect complications, with all data systematically recorded. Visual function typically improved gradually, with mild redness, mucous discharge, or transient photophobia common in the early days. Key postoperative parameters included visual function, owner satisfaction, and complications. Dogs were examined daily for the first three days, then on days 7, 14, 21, 30, and 60. On day 30, an extended neuro-ophthalmologic assessment was performed, including bright light, palpebral reflex, menace response, tracking, and a custom visual function test. Visual function was assessed for each eye individually considering: the visual function test which included the following steps: (i) assessment of light perception and tracking at three distances (very near, 1 m, and 5 m); (ii) detection of hand or finger movement to evaluate response to moving stimuli; (iii) peripheral vision testing by moving an object from behind toward the lateral visual field; and (iv) evaluation of light perception and tracking under complete darkness to assess visual adaptation to low light.

The test was performed repeatedly at postoperative intervals: days 1–3, 7, 14, 21, 30, and 60 with visual function scale (see also Supplementary Materials Table S2):

▪

V0—complete blindness, no light perception or detectable visual response;

▪

V1—minimal visual perception: light or object detected but not followed; poor near and distant vision;

▪

V2—moderate visual perception: light or moving object detected and followed; vision present at ≥1 m but poor at close range;

▪

V3—good visual function: light or objects clearly detected and tracked at both near and far distances (≥1 m).

2.13. Statistical Methods

The collected data were organized into tables and analyzed statistically using Student’s t-test and ANOVA, assuming independence and normality, as well as Pearson’s chi-squared test. All analyses were performed using SPSS Statistics for Windows, Version 17.0 (SPSS Inc., Chicago, IL, USA). A p-value < 0.05 was considered statistically significant.

3. Results

3.1. Surgical Method

Cataract removal in dogs was performed using phacoemulsification, which fragments the opacified lens with high-frequency ultrasonic energy, followed by aspiration of cortical remnants through the phaco handpiece. Two techniques—monomanual and bimanual—were employed to compare clinical efficacy and operative characteristics. The surgical method was applied consistently throughout the study, with no significant variation across years (χ² = 1.289, p = 0.732). Statistically significant associations were observed between technique and dog breed (χ² = 61.616, p = 0.009), experimental group (χ² = 60.000, p < 0.001), and cataract stage (χ² = 30.000, p < 0.001), supporting the rationale for grouping animals into four experimental sets (L1–L4)based on cataract maturation and surgical approach, as described before.

3.2. Indicators for Quantifying Surgical Duration

Surgical efficiency, a key factor in operative success, was evaluated using three temporal indicators: (1) operative scoring, (2) total duration of each cataract surgery, and (3) duration of each operative phase (T1–T4) according to the technique used.

Operative time scoring: Times were recorded for each eye (OD/OS) and assigned scores based on Table S2 (see Supplementary Materials): 1 (<3 min), 2 (4–5 min), 3 (5–10 min), 4 (10–20 min), 5 (>20 min). The mean surgery duration was 11.8 ± 0.75 min, with 6 procedures under 5 min and 68 under 7.5 min.

Total surgical duration by experimental group: Group 1 had the highest mean operative time, while Group 4 had the lowest (

Table 2. Mean and variability of surgical time across study groups.

Group	N	Mean (min)	Std. Deviation	Std. Error	Min.	Max	95% Confidence Interval for Mean
							Lower Bound	Upper Bound
L1	30	16.00	12.57	2.29	4.00	49.00	11.31	20.69
L2	30	14.17	7.06	1.29	6.00	29.00	11.53	16.80
L3	30	8.73	4.07	0.74	5.00	22.00	7.21	10.25
L4	30	8.30	3.27	0.60	5.00	21.00	7.07	9.52
Total	120	11.80	8.28	0.76	4.00	49.00	10.30	13.30

). Differences among groups L1–L4 were statistically significant (F = 7.643, p = 0.00). Longer durations in Groups 1 and 2 reflected early study years when surgeon experience was still developing.

Duration of individual operative phases: Mean durations for Phaco 1 were about one minute longer than Phaco 2 (

Table 3. Mean and variability of surgical time across the studied surgical techniques.

Operative Phases/Surgery Technique		N	Mean	Std. Deviation	Std. Error	95% Confidence Interval for Mean
						Lower Bound	Upper Bound
T1	Phaco1	60	3.13	3.64	0.47	2.19	4.07
	Phaco2	60	1.67	0.98	0.13	1.41	1.92
T2	Phaco1	60	6.20	4.20	0.54	5.11	7.28
	Phaco2	60	7.57	5.57	0.72	6.13	9.01
T3	Phaco1	60	1.00	0.00	0.00	1.00	1.00
	Phaco2	60	1.00	0.00	0.00	1.00	1.00
T4	Phaco1	60	2.15	2.09	0.27	1.61	2.69
	Phaco2	60	1.10	0.39	0.05	0.99	1.20
Total time of surgical techniques	Phaco1	60	12.27	9.91	1.28	9.71	14.83
	Phaco2	60	11.33	6.29	0.81	9.71	12.95

), but the overall difference was not significant (t = 0.16, p = 0.540). Significant differences were found for T1 (t = 3.010, p = 0.003)and T4 (t = 3.823, p = 0.001), with Phaco 1 taking longer due to older dogs with thicker anterior capsules (T1)and the surgeon’s early experience with IOL implantation (T4).

Considering each operative phase and corresponding time-based score (Score 1 < 3 min; Score 2 = 4–5 min; Score 3 = 5–10 min; Score 4 = 10–20 min; Score 5 > 20 min), the following results were observed: the monomanual phacoemulsification technique showed shorter operative times in immature or intumescent cataracts (Group 1) and longer durations in mature or hypermature cataracts (Group 2) with complete preoperative blindness. Differences in mean operative durations among the four groups (L1–L4) were statistically significant (F = 9.363, p < 0.001).

3.3. Analysis of Operative Time Scores (T1–T4)

The bimanual phacoemulsification technique showed more efficiency, showing shorter T2 durations in mature and hypermature cataracts compared with the monomanual (Phaco 1)method. As with T1, surgical skill significantly influenced T2 duration, with advanced training reducing operative time.

Phase T1 Analysis. Analysis of T1, T2, and T4 operative time scores (Supplementary Materials Table S1) revealed a significant difference in T1 means (Δ = 0.35 min; t = 2.646, p = 0.009). The T1 score showed no significant association with breed, body size, weight, sex, neuter status, lens-induced uveitis (LIU), surgical technique, or IOL type. However, it was significantly associated with age (χ² = 48.716, p = 0.038), cataract stage (χ² = 18.626, p = 0.005), experimental group (χ² = 31.246, p < 0.001), pre-existing ocular disease (χ² = 9.445, p = 0.024), and study year (χ² = 51.915, p < 0.001).

Phase T2 Analysis. During T2, nucleus fragmentation was tailored to nucleus hardness (Table 3, Table 4 and Table 5). Such adjustments did not affect overall outcomes or corneal endothelial integrity [10,11]. Although the mean T2 difference was 0.23 min (t = 1.125, p = 0.263), no significant difference was observed between groups. The T2 score correlated significantly with body weight, sex, experimental group, LIU presence, pre-existing ocular pathologies, pathology type, study year, and total operative time. No associations were found with breed, body size, neuter status, age, cataract stage, surgical technique, IOL type, or intraoperative complications.

Phase T4 Analysis. At T4, a significant difference in mean scores was noted (Δ = 0.216 min; t = 3.023, p = 0.003), with associations identified for age and cataract maturity (χ² = 7.759, p = 0.101).

3.4. Implant Type and Phaco Technique

All cataract surgeries concluded with intraocular lens (IOL) implantation to replace the extracted natural lens. In dogs with bilateral cataracts of similar type, different IOL models were implanted in each eye, forming Experiment 2 of the study.

From a temporal scoring standpoint, no significant differences were found between the two IOL types in either phase duration or total operative time (t = 0.231, p = 0.8185). Thus, implant type did not influence surgical duration, though size availability was critical for anatomical compatibility. The Fo-X model’s broader range of smaller diameters provided better adaptability for small breeds, explaining its preferred use and the significant association between IOL type and breed (χ² = 62.937, p = 0.007), as well as between IOL type and cataract maturity (χ² = 30.000, p < 0.001).

3.5. Intraoperative Complications

All intraoperative complications observed during cataract surgery were documented and analyzed across the four experimental groups. The monitored complications included hyphema, rupture of the lenticular suspensory ligament, capsulorhexis defects, posterior capsule rupture, lens luxation into the vitreous, corneal endothelial touch, residual cortical material, and retinal detachment. The following intraoperative complications were systematically monitored (see Table 4).

Table 4. Summary of the frequency of intraoperative complications.

	Group
Intraoperative Complications	L1	L2	L3	L4
Hemorrhage within the anterior chamber (hyphema)	3	6	1	5
Rupture of the lenticular suspensory ligament	0	4	1	3
Defective capsulorhexis	5	4	1	2
Defective capsulorhexis	1	3	0	2
Lens luxation into the vitreous body	1	4	0	4
Corneal endothelial touch	2	1	0	3
Presence of unaspirated cortical remnants	0	2	1	1
Retinal detachment (retinal separation)	0	5	1	6
Total	12	29	5	26

Table 4. Summary of the frequency of intraoperative complications.

	Group
Intraoperative Complications	L1	L2	L3	L4
Hemorrhage within the anterior chamber (hyphema)	3	6	1	5
Rupture of the lenticular suspensory ligament	0	4	1	3
Defective capsulorhexis	5	4	1	2
Defective capsulorhexis	1	3	0	2
Lens luxation into the vitreous body	1	4	0	4
Corneal endothelial touch	2	1	0	3
Presence of unaspirated cortical remnants	0	2	1	1
Retinal detachment (retinal separation)	0	5	1	6
Total	12	29	5	26

Analysis of mean temporal scores indicated that intraoperative complications significantly prolonged surgical duration across all phases, with notable differences for T1 (t = 2.301, p = 0.023) and T2 (t = 2.131, p = 0.035), confirming their direct impact on surgical efficiency.

3.6. Postoperative Complications

Postoperative follow-up visits included systematic evaluation for any complications, with immediate therapeutic intervention initiated when feasible, except in irreversible cases such as retinal detachment. Each complication was monitored until day 60 post-surgery, and all findings were documented in Table 5.

Table 5. Frequency and distribution of postoperative complications on days 7, 30, and 60 after surgery.

No.	Postoperative Complications	Number of Cases at:
		Day 7	Day 30	Day 60
1.	Posterior capsular opacification	0	0	0
2.	Ocular hypertension/glaucoma	16	2	0
3.	Chemosis	0	0	0
4.	Fibrin deposits	2	1	0
5.	Corneal opacity	5	6	6
6.	Posterior irido-lenticular synechiae	0	0	0
7.	Astigmatism	6	6	6
8.	Hyphema	15	0	0
9.	Uveitis	18	5	1
10.	Retinal detachment	13	15	15
11.	Endophthalmitis	0	0	0
12.	IOL (intraocular lens) dislocation or decentration	1	1	1

Table 5. Frequency and distribution of postoperative complications on days 7, 30, and 60 after surgery.

No.	Postoperative Complications	Number of Cases at:
		Day 7	Day 30	Day 60
1.	Posterior capsular opacification	0	0	0
2.	Ocular hypertension/glaucoma	16	2	0
3.	Chemosis	0	0	0
4.	Fibrin deposits	2	1	0
5.	Corneal opacity	5	6	6
6.	Posterior irido-lenticular synechiae	0	0	0
7.	Astigmatism	6	6	6
8.	Hyphema	15	0	0
9.	Uveitis	18	5	1
10.	Retinal detachment	13	15	15
11.	Endophthalmitis	0	0	0
12.	IOL (intraocular lens) dislocation or decentration	1	1	1

Mild complications, including hyphema, ocular hypertension, postoperative glaucoma, and uveitis, resolved completely by day 60 post-surgery. In contrast, cases of corneal opacity or retinal detachment were unresponsive to medical treatment, resulting in total blindness (V0) at the 60-day follow-up.

3.7. Postoperative Visual Function

The visual function assessment included: (1) the maze test, evaluating spatial orientation and obstacle avoidance under photopic and scotopic conditions; (2) the visual placement test, assessing the paw-extension reflex when approaching a surface; (3) the menace response, measuring instinctive reactions to sudden hand movements toward the eyes; (4) the cotton ball test, assessing the ability to detect and follow moving stimuli; and (5) a self-developed test. Results of self-developed test were recorded for each eye (OD—right eye, OS—left eye) and are presented in Supplementary Materials Table S2. Strong correlations were identified among all five tests (unpublished results).

Based on postoperative visual function data for self-developed test with V0–V3 classes, the statistical analysis of the phacoemulsification techniques (Phaco1 vs. Phaco 2) did not underline significant association (χ² = 3.433, p = 0.330). The intraocular lens implantation (IOL1 vs. IOL2)was strongly associated with the postoperatice visual function at 1 (χ² = 89.079, p = 0.001), 7 days (χ² = 93.480, p = 0.001), 14 days (χ² = 96.955, p = 0.001), 21 days (χ² = 97.954, p = 0.001), 30 days (χ² = 100.267, p = 0.001) and 60 days (χ² = 100.267, p = 0.330) after surgery.

4. Discussion

The present investigation demonstrated that both monomanual and bimanual phacoemulsification techniques providedsafe and effective removal of cataractous lenses in dogs, with postoperative restoration of functional vision in 79.2% of eyes by day 60. The results emphasize that cataract morphology and nuclear density are the principal determinants of intraoperative behavior and visual prognosis, while surgical approach and surgeon experience modulate overall efficiency and the complication profile.

The bimanual technique (Phaco 2) provided superior anterior chamber stability, more efficient fluidics, and enhanced cortical cleanup, resulting in shorter mean operative times at the critical stages of capsulorhexis (T1) and IOL implantation (T4). These advantages were most evident in mature and hypermature cataracts, where zonular stress and capsular fibrosis increase surgical complexity. In contrast, monomanual phacoemulsification (Phaco 1) achieved excellent results in immature and intumescent cataracts, where lens material was softer and chamber maintenance was less challenging. These findings underscore the importance of tailoring the technique to the biomechanical properties of the lens and the degree of nuclear sclerosis.

Postoperative inflammation was mild and self-limiting, confirming the biocompatibility of the acrylic IOLs and the adequacy of perioperative anti-inflammatory management. The absence of posterior capsule opacification (PCO) or IOL decentration within 60 days indicates appropriate in-the-bag fixation and satisfactory capsular stability. Nevertheless, intraoperative complications, particularly posterior capsule rupture, zonular dehiscence, and corneal endothelial trauma, were directly correlated with prolonged T1 and T2 durations and with the small subset of eyes (V0) that remained blind at follow-up.

Comparison among experimental groups revealed the highest incidence of intraoperative complications in Groups 2 and 4, corresponding to advanced cataract stages. This finding supports the conclusion that early surgical intervention, during the initial stages of lens opacification, significantly reduces intraoperative risk. Within these groups, complications were more frequent in Group 4, particularly when using the monomanual phacoemulsification technique, where dense nuclei increased the likelihood of endothelial trauma and incomplete cortical aspiration. Conversely, the bimanual technique provided superior intraocular control and safety, making it the preferred approach for advanced cataracts characterized by reduced zonular elasticity and capsular rigidity.

From a refractive standpoint, both foldable hydrophilic–hydrophobic acrylic IOLs provided excellent centration and optical clarity. The Fo-X model, featuring a broader dioptric range and optimized haptic geometry, achieved more predictable emmetropia in small-breed dogs and greater depth of focus under scotopic conditions.

The MD4 lens also demonstrated excellent intraoperative handling and optical performance, but its more limited range of available diameters reduced adaptability across extreme ocular sizes. This finding highlights the clinical importance of aligning IOL configuration with ocular anatomy and capsular bag dimensions to ensure optimal stability and refractive outcomes. In addition, the visual scoring system proposed here provides a clinically applicable and repeatable method for grading visual recovery, integrating behavioral and reflex-based parameters that better reflect functional vision rather than anatomical success alone.

Taken together, these findings substantiate that modern phacoemulsification with in-the-bag IOL implantation remains the gold-standard technique for canine cataract extraction, provided that the procedure is adapted to cataract maturity and ocular anatomy.

4.1. Discussions About Surgical Methods

The results of this study are largely consistent with previously published data in veterinary ophthalmology, confirming the safety and efficacy of phacoemulsification with foldable acrylic intraocular lens implantation as the current gold standard for canine cataract surgery. Reported success rates in the literature range from 85% to 95% of eyes achieving functional vision after surgery, with long-term maintenance of vision in approximately 80–85% of cases [10,11]. Recent studies further validate these outcomes: a 2025 cohort involving 31 dogs (48 eyes) documented 83.9–87.5% success, emphasizing the importance of early postoperative IOP monitoring and inflammation control [3]. The 79.2% functional vision recovery observed in the present study after 60 days falls within this range, confirming comparable clinical efficacy under practical field conditions.

In agreement with Slatter (1990) [9] and Nasisse & Davidson (1990) [12], the present findings reinforce that early surgical intervention, during the immature or intumescent stages of cataract formation, substantially reduces intraoperative risk and postoperative inflammation. Advanced cataracts (Groups 2 and 4) exhibited higher rates of intraoperative complications, particularly when managed with the monomanual technique. This observation mirrors prior reports that nuclear sclerosis and capsular fibrosis increase the risk of posterior capsule rupture and endothelial trauma in mature and hypermature lenses. Similarly, Edelmann et al. (2022) demonstrated that higher cumulative dissipated energy (CDE) during phacoemulsification is associated with more complications and poorer visual outcomes, supporting the concept that dense, sclerotic nuclei pose greater surgical risk—consistent with our own data [1].

The current results also corroborate with other findings [13,14] who emphasized the superior intraocular control provided by bimanual phacoemulsification systems. In this study, the bimanual approach led to shorter operative times in the capsulorhexis and IOL implantation phases (T1 and T4) and fewer intraoperative complications in dense nuclei, confirming its value for advanced cataracts. Conversely, monomanual phacoemulsification remained efficient and less invasive for soft or intumescent lenses, aligning with traditional veterinary surgical protocols. Recent technique-focused literature in veterinary and human ophthalmology continues to advocate for improved chamber stability, controlled fluidics, and enhanced cortical aspiration—principles directly reflected in our surgical outcomes.

The pattern of postoperative complications observed here also parallels recent reports. As described by Klein et al. (2011) [15], postoperative ocular hypertension, uveitis, and corneal opacities remain the most frequent transient sequelae, while retinal detachment and IOL decentration are uncommon but vision-threatening. Modern investigations highlight the same priorities: Kang et al. (2025) [3] showed significant IOP spikes within the first hours after surgery, and Liu et al. (2024) [5] demonstrated that intracameral triamcinolone acetonide effectively reduces postoperative inflammation, corneal edema, and transient ocular hypertension. These findings complement our observation of mild, self-limiting inflammation and underscore the importance of anti-inflammatory protocols and close IOP surveillance during early recovery. The absence of posterior capsule opacification (PCO) within 60 days in our cohort agrees with the low short-term PCO rates reported for modern hydrophilic–hydrophobic acrylic IOLs.

Regarding intraocular lenses, the comparison between the Fo-X and MD4 models reflects both earlier and contemporary refractive studies. Kaminsky et al. (2023) demonstrated that the Fo-X lens achieves near-emmetropic outcomes and stable centration across postoperative intervals [2]. The present data confirm these tendencies, showing slightly superior refractive predictability for Fo-X, while the MD4 lens also performed excellently, its only limitation being the narrower range of available diameters. This observation supports the recommendation that IOL selection be individualized according to ocular anatomy and breed size, consistent with the latest prospective evaluations of canine IOL performance.

Finally, the present study supports the earlier conclusions of Appel (2006) [16] and Beteg et al. (2006) [17] regarding the evolution of phacoemulsification outcomes in veterinary ophthalmology: as techniques, instrumentation, and surgeon training have advanced, complication rates have decreased, and functional recovery has become more predictable. The temporal improvement observed across study years in our data reflects the same learning-curve phenomenon described by Nasisse & Davidson (1990) [12] and echoed by newer reports, emphasizing the continuous refinement of surgical proficiency as a determinant of postoperative success.

Overall, the alignment between our results and both classical and recent literature underscores the clinical maturity of modern phacoemulsification protocols and validates the use of both monomanual and bimanual approaches—appropriately selected based on cataract types, reliable, evidence-based methods for restoring vision in dogs with cataracts.

4.2. Comparison of Surgical Duration with Previous Literature

The mean operative duration obtained in the present study (11.8 ± 0.75 min) corresponds closely with values reported in recent veterinary ophthalmology literature and reflects a high degree of surgical efficiency. Modern studies indicate that the average time required for phacoemulsification with IOL implantation in dogs varies between 10 and 20 min per eye, depending on cataract density, surgical technique, and the surgeon’s experience.

Edelmann et al. (2022) reported an average total surgical duration of approximately 12.5 min, with increased cumulative dissipated energy (CDE) correlating directly with longer procedures and a higher incidence of intraoperative complications [1]. This observation is consistent with our finding that Groups 2 and 4, corresponding to advanced cataract stages, exhibited significantly longer durations for T1 (capsulorhexis) and T4 (IOL implantation) phases and a higher complication rate.

A recent quantitative analysis by Kang et al. (2025) [3] recorded an average phacoemulsification time of 3.81 ± 0.42 min in 48 eyes, representing only the ultrasonic lens fragmentation and aspiration phases. This value is consistent with the intraoperative portions of our study, where the mean phacoemulsification time (T2) ranged between 6.20 and 7.57 min, depending on technique and nucleus hardness. The slightly longer T2 observed in our cases can be attributed to variations in cataract maturity and breed size, as well as the absence of ultrasonic time standardization.

The influence of operator experience on surgical duration is also well documented. Nasisse & Davidson (1990) [12] described a clear learning-curve effect in early surgical series, and this trend persists in more recent data. Our progressive reduction in operative time from Groups 1 to 4 parallels the temporal improvements observed in other reports and supports the notion that experience and refined handpiece control are decisive in optimizing efficiency.

In a complementary perspective, Liu et al. (2024) [5] demonstrated that adjunct use of intracameral triamcinolone acetonide not only reduces early postoperative inflammation but may also shorten effective surgical time by improving visualization and anterior chamber stability. This finding indirectly supports our observation of shorter and safer procedures under the bimanual technique (Phaco 2), where fluidic stability was superior.

Studies focusing on ultrasound energy and endothelial safety, such as Vlachomitrou et al. (2025) [18] and Preoperative and Intraoperative Risk Factors for Corneal Endothelial Loss (2025), further underline the relationship between prolonged phacoemulsification time, increased CDE, and endothelial trauma. These conclusions align with our finding that dense, hypermature cataracts—requiring longer T2 durations—are more prone to endothelial complications.

Although Andrews et al. (2025) [19] did not measure operative duration directly, their large-scale review of lens capsule disruptions (LCD) in 520 eyes reported a 27.8% incidence, reinforcing that complex or prolonged surgeries increase the likelihood of intraoperative capsule defects—findings that parallel the longer T1 and T4 durations in our advanced cataract groups.

From an anatomical standpoint, Kim et al. (2023) [4] demonstrated postoperative narrowing of the ciliary cleft following phacoemulsification, which could predispose to transient ocular hypertension. This observation supports the importance of minimizing intraoperative manipulation time, as prolonged procedures may exacerbate postoperative IOP fluctuations.

Overall, the mean total surgical duration recorded in our study is comparable to or slightly better than recent published averages. The observed trend toward reduced operative time and complication rate across study years confirms that surgical refinement, appropriate case selection, and the use of bimanual techniques significantly enhance operative efficiency while preserving ocular safety. These findings place the present data well within the upper range of performance reported in the most recent veterinary ophthalmic literature.

4.3. Analysis of Operative Time Scores (T1–T4)

Phase-specific durations recorded in this study are consistent with the ranges reported in recent veterinary ophthalmic literature. Edelmann (2022) documented mean total surgical durations of approximately 12.5 min, emphasizing that higher cumulative dissipated energy (CDE) correlates with prolonged phacoemulsification and increased complication risk [1]. Similarly, Kang et al. (2025) [3] reported a mean phacoemulsification time of 3.81 ± 0.42 min during nucleus fragmentation—corresponding closely to our T2 phase values (6.2–7.6 min), when considering total aspiration and irrigation time. The influence of surgical experience on T1 (capsulorhexis) and T4 (IOL implantation) durations mirrors the learning-curve effect described by Nasisse & Davidson (1990) [12] and confirmed by Ganekal & Nagarajappa (2011) [14], who found that procedural fluency significantly reduces time and variability in anterior capsule manipulation. Recent evidence also links shorter operative time to improved chamber stability and lower inflammatory response. Liu et al. (2024) [5] demonstrated that intracameral triamcinolone acetonide improves intraoperative visualization, shortens effective phaco time, and reduces postoperative corneal edema. This observation parallels our findings, where the bimanual technique yielded superior fluidic control and reduced T2 durations in dense cataracts.

Studies examining ultrasonic efficiency and endothelial safety—such as Vlachomitrou et al. (2025) [18] and Perone et al. (2024) [20]—highlight the clinical relevance of minimizing ultrasound exposure and total effective phaco time (EPT) to prevent endothelial cell loss. These findings align with Ren et al. (2021) [7], who identified prolonged EPT and phaco duration as independent predictors of short-term corneal endothelial cell loss in canine cataract surgery. Furthermore, Kim et al. (2023) [4] showed via ultrasound biomicroscopy that postoperative narrowing of the ciliary cleft and reduced aqueous outflow may predispose to ocular hypertension, particularly after extended intraocular manipulation. This supports the importance of minimizing operative time to reduce stress on anterior segment structures.

Collectively, these results confirm that the phase-specific durations (T1–T4) achieved in this study are within or superior to those reported in the latest literature. The data validate the efficiency and safety of modern bimanual phacoemulsification, reinforcing its role as the optimal approach for advanced canine cataracts with dense or fibrotic nuclei.

4.4. Implant Typeand Phaco Technique—Comparisons with Literature

All study phacoemulsification procedures concluded with intraocular lens (IOL)implantation to restore optical refraction and posterior chamber integrity following removal of the cataractous lens. In dogs with bilateral cataracts of comparable density and morphology, different IOL models were implanted in each eye, forming Experiment 2 of the study, allowing intra-individual comparison of anatomical and refractive outcomes. The type of implant did not influence surgical duration, though the range of available diameters was critical for achieving proper capsular bag adaptation and maintaining zonular symmetry. The Fo-X model, available in diameters from 10–14 mm, demonstrated superior adaptability for toy and miniature breeds, characterized by smaller axial globe dimensions and reduced capsular equatorial diameter. Conversely, the MD4 IOL, limited to 12–14 mm, provided optimal stability and centration in medium and large breeds, where the capsular bag is broader and zonular tension is higher.

The Phaco 2 (bimanual)technique was preferentially employed in small-breed dogs with mature or hypermature cataracts, where enhanced fluidic control, improved visualization, and reduced surge effect were advantageous for fragile capsules and dense nuclei. By contrast, the Phaco 1 (monomanual) technique remained efficient for immature cataracts with soft lens material and preserved capsular elasticity, where reduced manipulation minimized intraocular turbulence.

This distribution mirrored the intraoperative adaptation strategy previously emphasized in the veterinary literature by Slatter (1990) [9], Nasisse & Davidson (1990) [12], and later confirmed by Ganekal & Nagarajappa (2011) [14] and Kang (2025) [3], who demonstrated that technique selection should consider lens hardness, anterior chamber depth, and endothelial reserve.

From a temporal scoring perspective, neither implant type nor technique significantly altered the mean duration of the operative phases. The minor differences recorded reflected surgeon adaptation to nucleus consistency and individual ocular anatomy rather than intrinsic IOL characteristics. Similar results were reported by Davidson (1991) [10] and Appel (2006) [16], who observed that the IOL implantation phase contributed minimally to the total surgical time, while efficiency improved proportionally with experience and reduced phacoemulsification energy (CDE). Beteg et al. (2006) also demonstrated that anatomical matching between the implant and the capsular bag was more relevant for visual stability than model-specific design [17].

The current data are in line with modern reports. Edelmann (2022) [1] showed that implantation of foldable hydrophilic–hydrophobic acrylic IOLs can be performed in under one minute, without influencing total surgical duration, while Kaminsky et al. (2023) confirmed that both the Fo-X and MD-series (An-Vision GmbH)lenses provide predictable refractive outcomes, central positioning, and stable long-term biocompatibility [2]. Our observation that the Fo-X lens was preferred in smaller dogs, due to its extended size spectrum, reflects practical anatomical considerations consistent with manufacturer recommendations and the clinical observations regarding breed-adapted IOL selection [11,13].

From a functional standpoint, postoperative visual recovery did not differ significantly between IOL models. The overall visual success rate (79.16%)was comparable to historical data—82–85% functional vision reported by Klein et al. (2011) [15] and Gelatt & Wilkie (2011) [11]—and nearly identical to modern outcomes of Liu et al. (2024) [5] and Ren et al. (2021) [7], who found that long-term vision stability depends primarily on chamber stability, inflammation control, and precise in-the-bag positioning rather than IOL shape or material. Both studies confirmed that meticulous biometry and accurate axial length measurement are the primary determinants of postoperative refractive accuracy in dogs.

From a biomechanical perspective, recent investigations have refined understanding of IOL–endothelium interactions. Perone et al. (2024) [20] demonstrated that the lens insertion phase accounts for less than 10% of total endothelial stress compared with cumulative phacoemulsification energy, while Vlachomitrou et al. (2025) [18] linked excessive ultrasound time and anterior chamber instability to endothelial cell loss and secondary ocular hypertension. These observations corroborate the present findings that IOL type and implantation time had no measurable impact on operative duration or postoperative endothelial integrity (p = 0.8185).

In agreement with the evolutionary trend of the field, Davidson (1991) [10] and Slatter (1990) [9] described early PMMA IOLs as mechanically stable but surgically demanding due to larger incisions and capsule stretch. Contemporary foldable acrylic models—exemplified by the Fo-X and MD4 lenses—have reduced incision size, minimized zonular stress, and shortened the intraocular manipulation time, as highlighted by Appel (2006) [16] and Kaminsky (2023) [2]. Our findings confirm that modern IOL technology, combined with controlled fluidics and tailored sizing, eliminates the operative time penalty once associated with lens implantation.

Taken together, these data indicate that the implantation phase has become a brief, safe, and predictable step in modern canine phacoemulsification. The choice between Fo-X and MD4 should be guided by ocular biometry, breed morphology, and capsular bag diameter, rather than by concern over surgical time. The Fo-X remains preferable for small eyes requiring shorter optics and reduced haptic expansion, while the MD4 provides excellent posterior capsule coverage in larger globes. These results corroborate the ongoing refinement of canine cataract surgery as described by Gelatt & Wilkie (2011) [11] and extended by Kaminsky (2023) [2]–confirming that current phacoemulsification and IOL implantation protocols have reached a level of ophthalmic precision and reproducibility comparable to those in human anterior segment surgery.

4.5. Intraoperative Complications, Interpretation and Comparisonwith Previous Literature

All intraoperative complications recorded during cataract surgery were analyzed across the four experimental groups, including hyphema, zonular rupture, capsulorhexis defects, posterior capsule rupture, lens luxation, corneal endothelial touch, residual cortical material, and retinal detachment (Table 4). The total number of complications was highest in Groups 2 and 4, corresponding to advanced cataracts, while Groups 1 and 3 (immature cataracts)exhibited fewer events. Intraoperative complications significantly prolonged surgical duration, particularly in T1 and T2, confirming their direct effect on surgical efficiency. The most frequent adverse events were capsulorhexis irregularities and hyphema, whereas posterior capsule rupture and lens luxation occurred mainly in hypermature lenses with dense nuclei.

These findings are consistent with previous studies in both veterinary and human ophthalmology, which report higher complication rates in mature cataracts due to nuclear sclerosis, zonular weakening, and capsular fibrosis [3,9,12]. Similar observations were made by Ganekal & Nagarajappa (2014) [14] and Edelmann (2022), who associated prolonged ultrasound time and limited visibility with increased endothelial stress and capsular fragility [1]. In contrast, early surgical intervention during the immature stage minimizes intraocular turbulence, reducing the risk of posterior capsule rupture and endothelial trauma [5,7].

The bimanual phacoemulsification technique provided greater chamber stability and nuclear control, showing fewer complications in dense cataracts compared to the monomanual approach, which remains adequate for softer lenses. These results mirror recent reports by Vlachomitrou (2025) [18] and Perone (2024) [20] in human studies, confirming that optimal energy modulation and dual-handpiece coordination reduce intraoperative endothelial damage.

Overall, the complication profile in this study aligns with established literature, underscoring the importance of early surgical timing, refined technique selection, and adequate chamber stability for minimizing intraoperative risk in canine cataract surgery.

4.6. Postoperative Complications Discussions

The postoperative complications observed over the 60-day follow-up were consistent with the typical inflammatory and mechanical sequelae described in canine cataract surgery. Most events occurred during the early postoperative phase (days 1–7) and decreased progressively following appropriate medical therapy. Mild complications such as hyphema, ocular hypertension, uveitis, and transient corneal edema resolved completely by day 60, while irreversible lesions—mainly retinal detachment and persistent corneal opacity—resulted in complete visual loss (V0) at the final evaluation.

The overall profile of postoperative reactions in this study mirrors that reported by Gelatt & Wilkie (2011) [11], who identified anterior uveitis, corneal opacity, and ocular hypertension as the most common short-term complications after canine phacoemulsification. Davidson (1991) [10] and Nasisse & Davidson (1990) [12] described similar transient inflammatory reactions that typically subsided within two months under topical anti-inflammatory therapy. Our data confirm these trends, showing full remission of uveitis in 94.4%of affected eyes and normalization of intraocular pressure (IOP) in all cases by day 60.

The temporary increase in IOP (13.3%on day 7) reflects the early postoperative hypertensive phase observed in other studies. Kang et al. (2025) [3] demonstrated that postoperative ocular hypertension occurs in up to 15–18% of canine eyes following phacoemulsification and is often associated with viscoelastic retention, fibrin deposits, or inflammatory trabeculitis. Similarly, Liu et al. (2024) reported that intracameral triamcinolone significantly reduces both early IOP peaks and persistent anterior chamber flare by stabilizing the blood–aqueous barrier [5]. The absence of glaucomatous damage in our cohort at 60 days supports the efficacy of prompt anti-inflammatory and hypotensive therapy.

Corneal opacities persisted in approximately 10%of eyes and represented the main cause of incomplete visual recovery in otherwise anatomically successful surgeries. These findings align with the 8–12%incidence reported by Klein et al. (2011) [15] and Edelmann (2022), who identified endothelial cell loss and prolonged ultrasound exposure as principal etiological factors [1]. Modern analyses by Vlachomitrou et al. (2025) [18] and Perone et al. (2024) [20] confirm that excessive effective phaco time (EPT) and cumulative dissipated energy (CDE) are independent predictors of postoperative corneal decompensation. The pattern observed in our study—stable corneal transparency in short procedures and residual opacity in longer ones—supports these conclusions.

The complete absence of posterior capsule opacification (PCO)at 60 days is consistent with early follow-up data from Kaminsky et al. (2023) [2], who demonstrated minimal short-term PCO formation with hydrophilic–hydrophobic acrylic IOLs such as Fo-X and MD4. As Gelatt & Wilkie (2011) [11] noted, PCO typically develops beyond the 3-month mark, suggesting that longer follow-up is required for definitive assessment.

Retinal detachment (RD) represented the most severe postoperative event, with 15 persistent cases. These detachments were often secondary to intraoperative complications—chiefly posterior capsule rupture or vitreous loss—and mirror the 8–10% incidence reported in classic series [15,16] as well as the more recent findings of Andrews et al. (2025) [19], who documented RD in 12.4%of eyes after lens capsule disruption. Kim et al. (2023), using ultrasound biomicroscopy, demonstrated that ciliary cleft narrowing and vitreoretinal traction following phacoemulsification can predispose to delayed retinal separation, supporting the hypothesis that subclinical trauma during surgery contributed to the late-onset detachments seen here [4].

IOL decentration or destabilization occurred in only one case (0.8%), confirming the excellent capsular stability of modern foldable acrylic implants. Comparable rates (<1%) have been reported by Edelmann (2022) [1] and Kaminsky (2023) [2] in eyes with in-the-bag fixation.

In the broader context of canine cataract surgery, the complication rates recorded in this study align closely with both historical and contemporary data. Gelatt & Wilkie (2011) [11] reported overall postoperative complication frequencies of 25–30%, while modern cohorts [1,7] describe values ranging between 18–22%under optimized energy and fluidic control. The total incidence observed here (~20%) thus reflects an evidence-based improvement in safety and predictability, consistent with current phacoemulsification standards.

Collectively, these results emphasize that postoperative inflammatory and mechanical complications are largely transient and controllable, provided early intervention and rigorous monitoring are implemented. Persistent complications such as corneal opacity and retinal detachment remain the primary causes of permanent visual loss. Their occurrence underscores the critical interplay between intraoperative control, energy modulation, and postoperative anti-inflammatory management—core principles echoed throughout the veterinary ophthalmic literature from Slatter (1990) [9] to Vlachomitrou (2025) [18].

Since the nature and severity of postoperative complications directly influence visual recovery, the subsequent section focuses on the analysis of functional vision outcomes. This includes the correlation between postoperative ocular integrity, inflammatory control, and the degree of visual restoration achieved by day 60.

4.7. Interpretation and Comparison with Previous Literature of Visual FunctionResults

The multimodal visual assessment employed in this study—comprising the maze test, visual placing, menace response, cotton ball tracking, and the newly developed behavioral scale (V0–V3)—allowed an integrative evaluation of postoperative visual recovery, consistent with contemporary standards in veterinary ophthalmology. Strong inter-test correlations confirmed the reliability of these functional metrics for assessing post-surgical visual rehabilitation. The overall visual recovery rate of 79.16% (V2–V3 categories)at 60 days post-surgery corresponds closely to the success rates reported in earlier literature. Davidson (1991) [10] and Nasisse & Davidson (1990) [12] described 85–90% of canine eyes achieving functional vision following phacoemulsification, while Gelatt & Wilkie (2011) [11] reported long-term vision retention in 80–85% of operated eyes. Our slightly lower rate reflects the inclusion of hypermature cataracts (Groups L2 and L4), which are associated with a higher incidence of intraoperative and postoperative complications.

The absence of a statistically significant association between phacoemulsification technique (Phaco 1 vs. Phaco 2, p = 0.330) suggests that both approaches provided comparable visual outcomes when surgical energy and chamber stability were appropriately controlled. This finding is in line with Ganekal & Nagarajappa (2014) [14] and Kang (2025) [3], who reported that bimanual systems improve fluidic control and reduce endothelial cell loss, but do not necessarily translate into superior visual scores when surgery is performed by experienced operators.

By contrast, the strong correlation between IOL type and postoperative visual function across all evaluation points (p < 0.001)underscores the clinical relevance of anatomical and refractive compatibility between the implant and the capsular bag. This observation corroborates the findings of Kaminsky et al. (2023) [2], who demonstrated that the Fo-X IOL achieves near-emmetropic outcomes and stable centration in small- and medium-breed dogs, while MD4 lenses, though optically equivalent, show reduced adaptability in miniature breeds due to limited size range. Similarly, Edelmann (2022) [1] confirmed that visual outcome is optimized when IOL selection is guided by precise ocular biometry and capsular tension equilibrium, independent of the phacoemulsification system employed.

From a functional perspective, our findings parallel those of Klein et al. (2011) [15], who observed that approximately 80–85%of eyes recovered measurable vision (positive menace and obstacle avoidance), while permanent blindness occurred in 10–12%of cases, primarily due to retinal detachment or persistent corneal opacity. The same pattern was observed in our series, where irreversible visual loss (V0) corresponded to eyes with intraoperative capsule rupture or retinal detachment.

Contemporary analyses provide additional mechanistic insight. Vlachomitrou et al. (2025) [18] and Perone et al. (2024) [20] emphasized that extended effective phaco time (EPT)and elevated cumulative dissipated energy (CDE)are independent predictors of delayed visual recovery due to endothelial damage and postoperative optical aberrations. The shorter recovery period observed in our bimanual cases (Phaco 2) may thus reflect more efficient nuclear fragmentation and reduced ultrasonic energy transfer.

Overall, the present findings confirm that functional visual recovery in dogs after cataract surgery is determined primarily by IOL fit and postoperative ocular stability, rather than by the choice of phacoemulsification technique. The strong and sustained association between IOL model and visual score at each postoperative time point validates the importance of individualized IOL selection, based on ocular biometry and breed-specific anatomy.

These outcomes are consistent with the progressive refinement of phacoemulsification techniques and lens technologies described from Slatter (1990) [9] to Kaminsky (2023) [2], reflecting the contemporary standard of care in veterinary ophthalmology where over 75–85% of dogs regain functional vision, and long-term outcomes increasingly approach those achieved in human anterior segment surgery.

4.8. Clinical Implications

Despite continuous refinement of surgical technology, training disparities remain a defining factor in the choice and performance of phacoemulsification techniques. As highlighted by Slatter (1990) [9] and reiterated by Gelatt et al. (2022) [13], veterinary ophthalmology training is still limited in exposure to complex anterior segment surgery compared with human ophthalmology. Recent analyses confirm this educational gap: Hsu et al. (2025) [21] emphasized that the absence of standardized curricula and limited access to bimanual instrumentation during veterinary residencies restrict surgeons’ability to acquire two-handed coordination, which remains crucial for advanced cataract extraction. Consequently, the monomanual technique continues to predominate in everyday veterinary practice—favored for immature cataracts, where lens softness and capsular stability make it both safe and time-efficient.

Conversely, in human ophthalmology, bimanual phacoemulsification has long become the procedural norm. According to Ganekal & Nagarajappa (2014) [14], approximately 46% of surgeons perform the quadrant division technique and 20% the stop-and-chop method, both optimizing nuclear fragmentation and minimizing stress on the capsular bag. When capsular support is insufficient, scleral fixation of intraocular lenses is used in nearly 30% of human cases, illustrating the procedural adaptability that accompanies broader surgical training.

Modern simulation-based education further amplifies this difference. The Yaïci et al. (2024) [22] study demonstrated that high-fidelity virtual reality simulators for phacoemulsification (such as the HelpMeSee platform) can reliably distinguish expert from novice performance, providing a reproducible, risk-free environment for surgical training. Incorporating similar simulation modules and structured bimanual wet-lab exercises into veterinary residency programs would standardize learning curves and align outcomes with human ophthalmic benchmarks.

In line with Lim (2011) [23], refinement of surgical training in bimanual phacoemulsification remains a key priority for improving consistency and ensuring safe transition from simulation-based proficiency to live surgery.

Moreover, recent comparative human data, such as the 2024 Phaco-Chop versus Divide-and-Conquer trial, reinforce that advanced nucleus disassembly strategies can significantly reduce effective phacoemulsification time and endothelial trauma—principles directly transferable to the optimization of veterinary protocols [22].

Collectively, these findings underscore that progress in veterinary cataract surgery depends not only on instrument technology but also on training methodology and surgical exposure. As accessibility to high-performance microscopes, viscoelastics, and phaco systems continues to improve, the next step in veterinary ophthalmology should focus on formalized microsurgical training, adoption of VR simulation, and standardization of bimanual technique instruction. This approach would bridge the gap between human and veterinary ophthalmology, ensuring both procedural safety and consistent visual outcomes across species.

Comparable trends have also been observed in human cataract surgery, where the 2024 Phaco-Chop versus Divide-and-Conquer Trial demonstrated that advanced nucleus disassembly techniques can significantly reduce effective phacoemulsification time and endothelial cell loss [24]. These findings further validate the importance of continuous refinement of surgical methodology and energy modulation strategies in both human and veterinary ophthalmology.

The findings of this study confirmed the initial hypothesis that bimanual phacoemulsification (Phaco 2) enhances intraoperative control and reduces complication rates in advanced cataracts, particularly during capsulorhexis and intraocular lens implantation. Although total surgical duration did not differ significantly, the bimanual approach provided greater safety and efficiency in dense nuclei, while the monomanual technique (Phaco 1) showed simpler, faster, and fully effective for immature cataracts, where lens consistency and capsular stability allow safe manipulation with a single handpiece. Furthermore, the strong correlation between IOL type and visual outcome confirmed the clinical relevance of individualized lens selection based on ocular biometry and breed morphology. Overall, the results validate the hypothesis that refined surgical technique and tailored IOL selection are key determinants of predictable visual recovery and long-term ocular stability in canine cataract surgery.

This study provides practical guidance for optimizing canine cataract surgery. Monomanual phacoemulsification is ideal for immature cataracts, offering safety and speed, while bimanual phacoemulsification provides superior control in mature and hypermature cataracts. These results support a stage-based surgical approach and highlight the importance of biometry-driven IOL selection, where anatomical compatibility determines refractive success. Beyond clinical practice, the findings emphasize the need to strengthen microsurgical and bimanual training in veterinary ophthalmology through simulation and structured curricula, aligning outcomes with human surgical standards. Theoretically, this research advances the concept of precision ophthalmic surgery in animals—where individualized techniques, energy modulation, and lens design converge to ensure optimal and predictable visual rehabilitation.

Although conducted in a single veterinary center, this facility serves as the only specialized referral clinic in north-western Romania performing advanced phacoemulsification and intraocular lens implantation in dogs. As such, it receives a heterogeneous case distribution from a wide geographical area, encompassing diverse breeds, ages, and cataract morphologies. This regional representativeness partially compensates for the single-center limitation, while ensuring procedural standardization. Nevertheless, future multicentric studies will be required to confirm the external validity of these findings.

The 60-day follow-up adopted in this study was designed to capture the early and intermediate postoperative phase, when most inflammatory and mechanical reactions are expected to occur. However, late-onset complications such as posterior capsule opacification, capsular fibrosis, or delayed intraocular lens displacement typically develop over several months. Consequently, the selected timeframe allowed precise documentation of the critical healing phase and functional visual recovery, while acknowledging that future longitudinal investigations with extended monitoring will be essential to evaluate long-term capsular behavior, refractive stability, and delayed implant-related events.

The allocation of surgical technique and IOL type in this study was guided by cataract maturity and anterior segment integrity rather than by randomization, to maintain surgical safety in eyes with advanced lens sclerosis. Blinding of the surgeon was not feasible due to the evident differences between monomanual and bimanual phacoemulsification and the need to prepare specific IOL models preoperatively. As a result, some degree of selection and observer bias cannot be fully excluded. Furthermore, although univariate tests allowed detection of significant associations between operative phase duration, cataract stage, and technique, the construction of a comprehensive multivariate model was constrained by the bilateral design and the collinearity between surgical group, cataract maturity, and IOL selection. Future multicentric studies with larger, independently distributed cohorts will be better suited for regression-based adjustment for breed, age, and surgeon-related factors.

The main limitations of this study include the relatively short follow-up period (60 days) and the lack of long-term data on refractive stability or posterior capsule opacification. Future research should extend postoperative monitoring and include electrophysiological retinal evaluation. The absence of specular or confocal microscopy data represents a limitation, as it precluded detailed evaluation of postoperative corneal endothelial cell density and morphology following phacoemulsification.

Future studies should extend postoperative monitoring to assess long-term outcomes such as posterior capsule opacification and visual stability. Further research is needed to correlate phacoemulsification energy parameters with corneal endothelial health and to refine breed-specific IOL biometry and customization for improved refractive accuracy. The integration of simulation-based and bimanual surgical training should be systematically evaluated to enhance skill acquisition and reduce complication rates. Ultimately, combining multicentric data with predictive modeling may enable a new era of personalized ophthalmic surgery in veterinary medicine.

The comparative findings of this investigation align with established ophthalmic principles, indicating that phacoemulsification efficiency and intraocular lens stability depend on cataract maturity and zonular integrity, as reported by many authors [3,11,19]. The present results further demonstrate that bimanual techniques enhance anterior chamber stability and reduce capsular stress in dense nuclei, whereas monomanual approaches remain efficient for soft lenses with preserved capsular elasticity. These data contribute to a refined, stage-based surgical model for canine cataract extraction, bridging experimental and clinical ophthalmology. Future multicentric investigations with extended follow-up and standardized visual outcome metrics are warranted to validate these observations and to optimize long-term refractive predictability.

5. Conclusions

This study demonstrates that phacoemulsification with intraocular lens implantation remains a safe and effective method for restoring vision in dogs with cataracts. Surgical outcomes were influenced primarily by cataract maturity and ocular anatomy, while the surgeon’s experience and standardized technique provided procedural consistency.

The bimanual approach provided superior control and efficiency in advanced cataracts, particularly during capsulorhexis and IOL implantation, whereas the monomanual technique showed optimal performance for softer, immature lenses. Intraoperative complications were infrequent yet had prolonged surgery time when present, emphasizing the value of early intervention before cataract maturation.

Within 60 days post-surgery, approximately 80% of eyes recovered functional vision. However, complications such as retinal detachment led to vision loss in about 20%, indicating that further studies with longer follow-up and robust statistical design are needed to confirm safety and efficacy.