Search Results (6)

Background/Objectives: Femtosecond laser-assisted LASIK (FS-LASIK) is currently the most commonly performed procedure for the correction of myopia and myopic astigmatism. However, it inherently weakens the biomechanical integrity of the cornea due to flap creation and stromal ablation. This prospective study aimed to compare refractive and corneal biomechanical parameters after myopic FS-LASIK with different flap thicknesses and to identify parameters that may influence the change in corneal biomechanics after surgery. Methods: A total of 246 eyes were enrolled and divided into two groups based on flap thickness: 110 µm (n = 129) and 140 µm (n = 117). All procedures were performed using a femtosecond LDV Ziemer laser and standardized ablation profiles with similar ablation depths. Visual acuity, refractive outcomes, and corneal biomechanical parameters—corneal hysteresis (CH) and corneal resistance factor (CRF)—were assessed preoperatively and during a 6-month follow-up using the Ocular Response Analyzer (ORA). Multivariate regression analysis was used to identify predictors of biomechanical change. Results: The groups did not differ in preoperative values of the mean refractive spherical equivalent, keratometry, central corneal thickness, CH and CRF. At 6 months, both groups achieved comparable refractive outcomes, with no significant differences in uncorrected or corrected distance visual acuity, efficacy index and safety index. However, the thicker flap group exhibited significantly greater reductions in CH (−2.89 vs. −2.04 mmHg, p < 0.05) and CRF (−3.61 vs. −2.77 mmHg, p < 0.05), as well as greater biomechanical weakening per micron of ablation. Multivariate regression identified anterior weighted biomechanical index (AWBI) and flap thickness as the strongest predictors of CH reduction, while flap thickness, residual stromal bed thickness, ablation depth, and central corneal thickness contributed to CRF changes. Conclusions: While FS-LASIK with both flap thicknesses achieved equally effective visual outcomes, thicker flaps were associated with significantly greater biomechanical weakening. Flap thickness had a stronger influence on corneal biomechanics than ablation depth. These findings support consideration of flap thickness in surgical planning to optimize corneal biomechanical stability. Full article

Background/Objectives: Premium intraocular lenses (IOLs) are increasingly being selected for cataract and refractive lens surgery, but their functional performance depends critically on pupil size and corneal spherical aberration (SA). This study evaluates how these factors modulate the optical behavior of the RayOne EMV and Tecnis Synergy using a profilometry-based Through Object modulation transfer function (TO MTF) analysis. Methods: The surface profiles of the RayOne EMV and Tecnis Synergy were measured with a confocal optical profilometer and implemented in pseudophakic eye models via ray tracing. TO MTF at 50 cycles/mm was computed for object vergences from −4.0 D to +2.0 D over entrance pupil diameters from 2.0 to 5.5 mm in three corneal configurations derived from the Liou–Brennan model and ISO recommendations: mean population SA, aberration-free, and a myopic LASIK-like oblate cornea. Simulated optotype images were generated to relate TO MTF values to the expected distant, intermediate, and near visual performances. Results: RayOne EMV delivered high-quality distant image performance in all models. Its depth of focus increased only modestly and showed a strong dependence on pupil size. Intermediate and near vision rarely reached clinically acceptable levels. The Tecnis Synergy produced a broad depth-of-field plateau in distant to near visual performance for mean population spherical aberration at a 3.5 mm pupil. However, image quality at 90 cm remained limited. Optical performance worsened with increasing pupil size and positive spherical aberration, particularly under post-myopic LASIK conditions. Conclusions: The RayOne EMV behaves predominantly as a distance-oriented design with minimal true presbyopic benefit; the Tecnis Synergy provides a wider range of vision but is highly sensitive to corneal spherical aberration and pupil size, so thorough preoperative evaluation of corneal asphericity and functional pupil diameter is essential for IOL selection and power targeting. Full article

Background/Objectives: The purpose of this study was to investigate corneal biomechanical properties assessed with Corvis ST, structural features of myopia, and vessel density (VD) measured by optical coherence tomography angiography (OCT-A) and their associations with central visual function in myopic glaucoma patients. Methods: Forty-two eyes of 42 glaucoma patients with myopia without retinal lesions were subjected to analysis. Corvis ST was performed to measure the biomechanical properties of the eyeball. Superficial (retinal) and deep (choroidal) VDs in the peripapillary and macular regions were assessed using OCT-A, and retinal nerve fiber layer (RNFL) thickness was measured with OCT. The disc–foveal angle, disc torsion, and β-zone peripapillary atrophy (PPA) area were obtained from disc and retinal photography. Swedish interactive thresholding algorithm (SITA) 24-2 visual field (VF) testing was used to evaluate the function within the central 12 points. Results: A worse mean deviation (MD) from SITA 24-2 and higher whole-eye movement maximum from Corvis ST, representing deformable corneas, were associated with lower superficial peripapillary VD. A lower A1 deflection amplitude from Corvis ST, representing stiffer corneas, was associated with lower deep peripapillary VD. The sensitivity of the central 12 VF points was significantly associated with a larger disc–foveal angle, lower superficial peripapillary VD, and lower HC deformation amplitude from Corvis ST. Conclusions: Our preliminary findings suggest that more compliant corneas were associated with lower superficial VD, whereas stiffer corneas were associated with lower deep VD and central scotoma. Full article

Purpose: To evaluate the performance of traditional vergence formulas with segmented axial length (AL) compared to traditional composite AL in extremely long eyes, and to determine whether the segmented AL can be extended to the new-generation formulas, including the Barrett Universal II, Emmetropia Verifying Optical 2.0 (EVO2), Hill-RBF 3.0 (Hill3), Kane, and Ladas Super formula (LSF) formulas in extremely long eyes. Setting: National Hospital. Organization, Tokyo Medical Center, Japan. Design: Retrospective case series. Methods: Consecutive patients who underwent uncomplicated cataract surgery implanted with a three-piece intraocular lens between December 2015 and March 2021 were retrospectively reviewed. The composite AL was measured with a swept-source optical coherence tomography (SS-OCT) biometer using a mean refractive index. The segmented AL was calculated by summing the geometric lengths of the ocular segments (cornea, aqueous, lens, and vitreous) using multiple specific refractive indices based on the data obtained by the SS-OCT-based biometer. When refraction was measured at three months postoperatively, the median absolute errors (MedAEs) were calculated with two ALs for each formula. Results: The study included 31 eyes of 22 patients. The segmented AL (30.45 ± 1.23 mm) was significantly shorter than the composite AL (30.71 ± 1.28 mm, p < 0.001). The MedAEs were significantly reduced when using segmented AL for SRK/T, Haigis, Hill3, and LSF, compared to those obtained using composite AL (0.38 vs. 0.62, 0.48 vs. 0.79, 0.50 vs. 0.90, 0.34 vs. 0.61, p < 0.001 for all formulas, respectively). On the contrary, the MedAE obtained by Kane with segmented AL was significantly worse compared to the one with composite AL (0.35 vs. 0.27, p = 0.03). Conclusion: In extremely high myopic eyes, the segmented AL improves the performance of SRK/T, Haigis, Hill3, and LSF formulas compared to the composite AL, while the segmented AL worsens the prediction accuracy of the Kane formula. Full article

Various diffractive, refractive and holographic optical elements, such as diffraction gratings; microlens raster; phase plates; multi-order diffractive optical elements; adaptive mirrors; diffractive and refractive axicons; holographic multiplexes and many others are used to analyze wavefront aberrations. We shortly discuss the features (advantages and disadvantages) of various wavefront aberration sensors in the Introduction. The main part of the paper is devoted to the analysis of the weight coefficients of Zernike polynomials obtained during medical examinations of the cornea in the human eye. Using data obtained by aberrometers, the average values of the Zernike polynomial coefficients for the anterior and posterior surfaces of the healthy eye cornea and a myopic one were calculated. The original wavefront for the anterior and posterior surfaces of the cornea was restored separately, as well as the total wave aberration. For an objective assessment of the quality of vision, the corresponding point spread functions (PSFs) were calculated. We propose to compensate for the aberrations of the myopic eye, taking into account the physical features of the corneal surface. The results of numerical simulation showed that in order to improve the quality of the patient’s vision, it is necessary to take into account high-order aberrations of the anterior surface of the cornea in the form of a coma of the third order and aberrations of the fourth order. Full article

The purpose of our study was to evaluate the safety, effectiveness, predictability, and stability of myopic and astigmatic laser-assisted in situ keratomileusis (LASIK) with simultaneous prophylactic corneal cross-linking (CXL) in thin corneas. In total, 100 eyes from 50 patients who were subjected to myopic and astigmatism femtosecond LASIK with simultaneous prophylactic CXL were included. The design of the study was retrospective, longitudinal, and observational. All patients had a 48-month follow-up. The MEL 80 excimer laser was utilized with the Aberration Smart Ablation platform. CXL treatment was applied when the predicted stromal thickness was less than 330 µm. Patients’ mean age was 30.22 ± 5.97 years. Previous mean spherical equivalent was −5.50 ± 1.65 (−9.50 to −1.13) diopters (D). Postoperative mean spherical equivalent was −0.24 ± 0.29 (−0.85 to +0.50) D. Visual acuity (VA) of 20/20 or better was observed in 87% of the eyes and no eyes experienced VA loss. Spherical equivalent within ±0.50 D was observed in 93% of eyes, and 4% of eyes varied by 0.50 D or more between 3 and 48 months. Prophylactic corneal cross-linking with simultaneous femtosecond laser-assisted in situ keratomileusis in thin corneas proved to be effective, safe, and predictable. The results remained stable after 48 months of follow-up. Full article