Light Disturbance Analysis and Applications

Abstract

This narrative review synthesizes recent basic and clinical research on visual disturbances in low-light environments, highlighting the evaluation techniques for these conditions. It focuses on the degradation of visual acuity under dim lighting, exacerbated by pupil dilation, known as night vision disturbance (NVD). Key contributors to NVD include optical scattering, intraocular diffraction, ocular aberrations, and uncorrected refractive errors, all significantly impacting quality of life and functional abilities. This review also examines the effects of aging, eye disorders, surgical interventions, and corneal irregularities on NVD. It details the definitions, distinctions, and measurement methodologies for various optical phenomena, using both objective and subjective approaches, such as visual function questionnaires, simulators, and the light disturbance analyzer (LDA). The LDA is validated for clinical characterization and quantification of light distortion, proving useful in both clinical and research settings. This review advocates for continued innovation in therapeutic interventions to improve patient outcomes and alleviate the impact of visual disturbances.

1. Introduction

Light disturbance, characterized by visual phenomena such as glare, halos, starbursts, and decreased contrast sensitivity, significantly impacts visual performance, especially under low-light conditions when the pupils dilate [1]. Contrast sensitivity is crucial for discerning objects in low-light conditions, yet intense light sources can lead to the perception of dysphotopsias—visual disturbances around those lights [2,3,4]. These disturbances are of paramount concern in the field of visual science due to their profound effect on nighttime driving, reading ability in dim lighting, and overall quality of life [5,6,7].

Visual disturbances in low-lighting conditions can stem from various sources, including intraocular diffraction of light, ocular aberrations, and uncorrected refractive errors [3]. The pupil’s dilation in dim lighting exacerbates these effects, especially at night against a dark background, underscoring the importance of understanding and quantifying these disturbances accurately.

Along with diffraction and aberrations, light scattering is also a factor that contributes to the degradation of retinal image quality. Light scattering occurs in the cornea [8] and especially in the lens of the human eye [9]. The cornea is the first optical surface of the eye [10] and has a significant and crucial role in the formation of the visual image. The curvature of the cornea contributes to approximately two-thirds of the eye’s focusing ability. Consequently, any irregularities in its shape or changes in transparency can impact the quality of vision [11,12]. The crystalline lens, the second most powerful refractive element of the eye, is also responsible for adjusting its shape to refract light to be focused on the retina when considering the focal distance (accommodation) [13]. While scattering is usually minimal in young, healthy eyes, it is recognized to increase with age. This increase is attributed to changes in the structure of the lens, often associated with cataract formation. Consequently, these changes in the lens can alter its optical properties and lead to an increase in scattering [14,15]. In addition to aging, ocular pathologies [4,16,17], surgical procedures (such as refractive surgery and intraocular lens implantation) [18,19,20], lenses for the control and progression of myopia [21], and multifocal contact lenses [22], among others, can increase ocular scattering and high-order aberrations, contributing to an increase in complaints of decreased contrast sensitivity and poor vision, particularly under dim light conditions [23,24,25,26,27]. Night vision disorders can also become a limiting factor in individuals with corneal irregularities caused by ectasia (such as keratoconus) or after refractive surgery. Variations in the corneal shape will induce optical aberrations, specifically spherical aberration and coma, which can lead to image degradation, especially in low-light conditions [1,3,17,28].

The human eye functions as a complex optical system where incoming light passes through different ocular media, such as the cornea and the lens. In cases of very intense light or from highly intense sources, excessive dispersion may occur, leading to a glare sensation. This, in turn, can cause visual discomfort and a decrease in visual acuity [29,30].

There is growing interest in assessing visual function in low-light conditions and in the presence of light sources that induce glare, halos, and other forms of light distortion, as documented and discussed in the literature [1]. This concern is tied to the quest for methods to enhance visual performance in demanding situations, such as nighttime driving or in environments with fluctuating lighting conditions. The initial attempt to subjectively assess and understand the patient’s perception of vision impairment at night and its impact on daily activities was through representations or drawings, as explained by Fan-Paul et al. [1]. Visual function questionnaires have also been developed, and aspects such as contrast sensitivity, photic phenomena such as halos around lights and glare, quality of night vision, impact on daily activities, and general satisfaction with vision can be included in these questionnaires [31,32]. The purpose of this review is to provide an overview of the current methods available for quantifying light disturbances, with a particular focus on the light disturbance analyzer (LDA). This review presents various devices used in clinical settings to assess visual disturbances, such as glare and halos, and discusses their applications across different fields of visual correction, including spectacle lenses, contact lenses, corneal refractive surgery, and intraocular lenses. By compiling and analyzing the studies that utilize these instruments, this review aims to highlight the contributions and limitations of each method, providing a comprehensive understanding of their role in clinical practice and research. The subsequent sections will explore these devices in detail, alongside relevant concepts and definitions related to visual quality in low-lighting conditions.

2. Concepts and Definitions

It is crucial to start by defining specific terms, considering the broad range of definitions and concepts that are sometimes applied inconsistently.

The term light disturbance (LD) was first referred to in an editorial written by Klyce in 2007 [33]. The concept refers to an optical effect in which light is deflected or distorted when passing through certain media, such as the atmosphere or other transparent media. This phenomenon often results from the formation of a ring of light around a luminous object [33], and in the eye, it is an indicator of visual quality [34,35].

The term night vision disturbance (NVD) is commonly used in the literature to describe the combined effects of glare disability and decreased contrast sensitivity on image degradation under scotopic or mesopic conditions. By grouping these two visual impairments under the term “night vision disturbance”, researchers and clinicians can better understand and address the complex challenges individuals face when navigating/working under low-light environments. This term highlights the interconnected nature of glare disability and decreased contrast sensitivity, both of which can significantly impact an individual’s ability to see clearly and safely in nighttime conditions. NVD can be defined based on the shape or size of the degradation that an intense light source produces subjectively and, therefore, according to the description by Fan-Paul et al. [1], the concept of “glare disability”, “contrast sensitivity”, and “image degradation” are grouped in the term [36]. The most common “image degradations” are halos and starbursts. The following paragraphs define different photic phenomena that might be contained in the generic concept of light disturbances or NVD.

2.1. Disability Glare

Technically, glare refers to the physical term referring to a light source, while disability glare is related to a subjective reduction in visual performance due to the glare source; Figure 1 [1]. It was decided by the Commission Internation de l’Eclairage (International Commission on Illumination) (CIE) on international consent that disability glare is precisely defined by the optical effect of light scattering as reflected in the point-spread function [37,38]. Discomfort glare, disabling glare, and blinding glare have significant implications for traffic safety, among other conditions. Optically, glare disability or disabling glare occurs when light from a source is scattered within the eye, causing a degradation in image formation on the retina and a reduction in its contrast, reducing the ability to perceive the original visual information [1]. In practical terms, it can make it difficult for drivers to perceive important details such as traffic signs, pedestrians, or other vehicles at night. In contrast to disabling glare, discomfort glare does not lead to a reduction in the ability to see visual information. Instead, it results in feelings of discomfort and fatigue when exposed to intense light. This type of glare can be distracting and reduce the ability to focus as well as reaction times [12]. The term blinding glare refers to the momentary loss of visual perception that persists even after the intense light exposure has ceased [39].

2.2. Starburst

Starburst refers to a visual phenomenon where bright lights, such as headlights or streetlights, appear to radiate streaks or rays of light and can lead to visual discomfort and a decrease in visual acuity, especially in situations such as nighttime driving or exposure to bright lights. Rather than observing a single, well-defined point of light, individuals may perceive these streaks or rays extending outward from the light source; Figure 1. The appearance of starbursts around light sources can vary among individuals and tends to be more prevalent in those with specific ocular conditions such as astigmatism and cataracts or those who have undergone ocular surgeries. In a surgical context, starbursts are often associated with a transient loss of transparency in the post-operative period [40,41]. In these instances, they appear to originate from the points where radial incision scars extend beyond the margins of the pupil [40]. However, starburst is also reported even among patients who have not undergone surgical procedures, especially when they are wearing glasses or contact lenses that are under-corrected [42,43].

2.3. Halo

Halos refers to a visual phenomenon characterized by the perception of luminous circles or rings around light sources; Figure 1. These circles or rings can appear as a result of light diffraction or scattering within the eye’s optical system. Halos are directly related to sources of glare in the visual field and are often seen around bright lights, such as headlights or streetlights, and can be particularly noticeable in low-light conditions [4]. Following refractive surgery, starbursts may appear as visual phenomena, but they are typically transient in nature. In contrast, halos can persist after the surgery as constant visual effects, and the extent of the halo is related to the size of the pupil and the diameter of the ablation zone (the treated area). If the dilated pupil is beyond the treated zone, the light can diffract as it enters the eye, causing the halo effect around the light sources [40,41]. Even in early surgical procedures with small ablation zones, such as radial keratotomies, patients can experience halos around light sources, particularly in low-light conditions. This occurrence is due to the dispersion of light when the treated area is not precisely aligned with the pupil under low-light conditions, resulting in the formation of halos [1,41,44].

Figure 1. Light source and the three categories of positive dysphotopsias, according to the FDA (Food and Drug Administration), respectively. Recreation from the original image from Chang and Huggins (2018) [45].

Figure 1. Light source and the three categories of positive dysphotopsias, according to the FDA (Food and Drug Administration), respectively. Recreation from the original image from Chang and Huggins (2018) [45].

2.4. Ocular Scattering

Ocular scattering is a complex optical phenomenon that affects image quality in the human eye. Its effects are compared to the effects of ocular aberrations, diffraction, and variations in the refractive index. This degradation of the image occurs due to the deviation of light from the theoretical rectilinear path, resulting from the inhomogeneities or non-uniformities present in the optical medium through which the light passes. Ocular dispersion is due to a combination of optical phenomena, including diffraction, refraction, and reflection. Small particles, foreign bodies, density fluctuations, and the roughness of the surface of the different ocular optical elements are mentioned as non-uniformities that act as potential microscopic scatterers. These inhomogeneities can interact with light, causing dispersion and, consequently, image degradation. The cornea and lens are fundamental to image formation on the retina, but when their transparency is compromised, they can become significant sources of scattered light, affecting the retinal image quality. However, there are other sources of ocular scattering, such as the iris, sclera, vitreous humor, and the retina itself, as shown in Figure 2 [4].

As previously mentioned, the retina is also regarded as a source of scattering, as the light that strikes is not entirely absorbed. Instead, a portion of the light is reflected to other areas of the retina, thereby contributing to intraocular scattering [46,47]. The measurement of ocular dispersion can be accomplished using optical methods such as the double-pass or Hartmann–Shack techniques. These approaches are objective, as they do not rely on the subjective responses of patients to assess the optical quality of the eye [4]. Straylight, on the other hand, is the result of the combined effects of light scattering within the optical media and diffuse reflectance from different layers of the fundus [48]. Straylight is the combined effect of light scattering in the optical media and the diffuse reflectance from the various fundus layers [48]. It refers to the light within the eye that scatters instead of following a direct path to the retina. It can also result from light entering the eye in oblique angles and can occur due to corneal irregularities, cataracts, or other ocular conditions.

Understanding phenomena such as dispersion, diffraction, and glare is crucial, especially for designing surgical procedures and developing visual corrections to compensate for changes in the optical quality of the eye. Many authors attempted to evaluate different devices and strategies for measuring the bothersome nature of NVD. However, there are some limitations to the methods and techniques used so far in measuring NVD. This includes a lack of standardization, subjectivity, insufficient scientific validity of certain tests, and difficulties in interpretation both for physicians and patients. Furthermore, many of the tests come with a high cost and do not correlate with the reported symptoms. While there are different methods available to quantify ocular scattering and other NVDs, few clinical reports validate these systems for their use in clinical practice [4]. The following sections will review some of the most commonly used techniques and devices to quantify, either objectively or subjectively, those phenomena.

3. Methods to Measure Night Vision Disturbances

To objectively assess and understand the subjective symptoms of pre- and post-operative visual disturbances, various tests have been created. Initially, the tests were based on subjective surveys and questionnaires to quantify the type and level of visual disturbance. Since then, more formal methods have been introduced, including psychometric tests and more detailed rating scales, to increase rigor in quantifying these disorders [1].

Table 1. Summary of existing tests for night vision disturbances assessment.

Test	Parameter Measured	Brief Description
Night Vision Recording Chart (NVRC) [1]	Size of halos and presence of starburst or other image degradations	Patients are asked to draw or describe their visual disturbances when looking at a light source, providing a subjective representation of their NVD.
Simulators [49,50]	Perception of photic phenomena (halos, glare, and starburst)	Software that simulates night driving or other scenarios where NVD might be pronounced, allowing patients to adjust settings to match their perception of disturbances, thereby quantifying the severity and nature of their NVD.
Van den Berg Straylight Meter [51]	Retinal straylight (disability glare)	Measurement of the light scatter in the eye, contributing to reduced contrast sensitivity and increased glare.
Night Vision Test [52]	Size of the glare	Evaluates the size of glare perceived by the patient, offering a quantitative measure of this specific night vision disturbance.
Starlight System [27]	Quantitative assessment of halos	Offers a quantitative measure of halo size around light sources, useful for understanding the extent of this common night vision disturbance.
Gutiérrez Halometer [36]	Effects of halos	Specifically designed to assess the impact of halos on vision, providing a disturbance index based on the patient’s perception under low-light conditions.
Vision Monitor (Metrovision) [53]	Size of halos	Measures the size of halos induced by glare sources, using circular white light sources to generate glare and assess its effect on vision.
Aston Halometer [30]	Extent of halos	Utilize a central LED and mobile tablet to quantify and analyze the extent of dysphotopsias, including halos, in various directions of vision.
Rostock Glare Perimeter [29]	Quantify the effects of glare	Measures the subject’s ability to distinguish the marker’s brightness from the light source.
Halometer: Halo v1.0 [54,55]	Size and intensity of the halos and glare	During the procedure, the subject identifies peripheral stimuli that appear randomly around a central point of high luminosity, displayed on a dark background of a monitor.
Light Disturbance Analyzer [34,56]	Determines the size, shape, and regularity of light distortion	Quantifies the distortion caused by light, providing metrics on the size, shape, and regularity of phenomena like halos and starbursts, and is based on a predefined algorithm assessing the distribution of light in the visual field.

LED = light-emitting diodes; NVD = night vision disturbances.

provides a structured summary of the various techniques employed in the assessment of NVD.

3.1. Night Vision Recording Chart

The first pictorial representations, illustrations, and graphic schemes were created at an early stage to quantify photic phenomena. One of these tests was the night vision recording chart (NVRC), designed to quantify NVDs such as halos and starbursts [57]. The test was designed to be conducted in a dimly lit environment to mimic conditions that exacerbate NVDs, unlike other tests with brightness sources that constrict the pupil, obtaining unrealistic results [58]. This test involves projecting a small circle from a projector in a low-light environment, where patients are asked to reproduce what they see on a table adapted from an Amsler grid. However, this representation relies on a personal illustration, which introduces variability in the results, depending on the individual’s drawing skills and perceptions. This subjectivity, while offering unique personal insights into the patient’s experience, poses challenges in the standardization and comparability of outcomes across different individuals. This also introduces complexities for clinical studies or investigations that strive for more objective outcomes, particularly in the longitudinal monitoring of patients and/or the categorization of various treatments and surgical interventions on NVDs.

3.2. Simulators

As mentioned above, the visual experience and subjective perception of optical phenomena tend to vary considerably between subjects, especially when assessing the severity and discomfort of the symptoms associated with NVDs. Various night vision simulators are available, offering individuals a platform to visually articulate their visual experiences at night. However, it is crucial to acknowledge that these simulators may be prone to patient biases, potentially leading to the overestimation or underestimation of the size of halos [59].

The use of simulators or electronic media for studying these phenomena has not been extensively explored or addressed in comparison to other methods [60]. While there are only a few studies on this particular approach, the scientific literature often discusses the use of the Halo and Glare Simulator and the Vision Simulator in post-implantation evaluations of presbyopia-correcting IOLs. The Halo and Glare Simulator (Eyeland-Design Network GmbH, Vreden, Germany) is a type of software that simulates a night-driving scenario [50]. This simulator allows patients to adjust the type, size, and intensity of the halo, starburst, and glare [49].

The Vision Simulator exposes patients to light sources identical to halometers and subjectively reproduces the patient’s perception of the photic phenomena. It also allows you to adjust the size, intensity, width of the ring, interval, and shape of the halo, as well as the size of the glare and halo and the length of the starburst’s radiant beam. In this case, the size and intensity of the phenomena are converted into numerical values [60].

Nonetheless, the literature also highlights certain drawbacks associated with these simulators. Among the limitations is the difficulty in accurately evaluating the optical phenomena associated with different types of intraocular lenses (IOLs), mainly because of the inability to continuously adjust the parameters, such as the ring width or the spacing between halos. Furthermore, the simulators’ lack of capability to modify the size and intensity of starbursts independently is cited as a significant limitation. An additional point of concern is the reliance on the patient’s memory rather than the direct observation of actual light sources, which could compromise the reliability and consistency of the findings [60].

Recognizing the limitations of computer media in simulating night vision disturbances is essential, including the restricted range of intensities and contrasts, which might not accurately reflect the real visual experiences and technological constraints that limit the replication of specific visual effects. Additionally, individual variations in visual perception can lead to discrepancies in how these simulations are experienced. Such limitations necessitate cautious use and validation of these tools, understanding that while they provide insights, their results need careful interpretation due to potential inconsistencies across different devices and environments. Despite these challenges, combining traditional methods like questionnaires with advanced simulators offers a more nuanced and interactive approach to studying visual phenomena [50].

Several methods and instruments to quantify the halo phenomena through objective measurements of the size and shape of light distortion under nighttime lighting conditions are detailed below.

3.3. Direct Compensation Method

The first publications are in regard to the direct compensation method and the study of straylight by van den Berg back in the late 1980s [61,62]. This psychophysical method was designed to objectively quantify the phenomena of light scattering and halo effects under nighttime conditions. This method operates on the principle of neutralizing the light scatter within the eye by introducing a compensatory light source. By meticulously adjusting this source until it offsets the scattered light perceived by the observer, researchers can accurately measure the extent of light distortion or straylight [61].

Conventional Straylight Meter (CSLM) and Computer-Implemented Straylight Meter (NSLM)

The CSLM (conventional) and NSLM (computer-implemented) straylight meters operate under van der Berg’s principles for quantifying retinal straylight or light scattering within the eye. Both utilize the direct compensation method to measure the intensity of straylight by compensating for the scattered light perceived by the observer. This is achieved by adjusting a light source in the device until the observer can no longer distinguish between the straylight and the background, allowing for the precise measurement of the eye’s scattering properties. Although both (CSLM and NSLM) measure retinal straylight based on the principles outlined by van der Berg, they incorporate different technologies and operational features. The CSLM (commonly referred to as the van den Berg straylight meter) is a small portable device that operates with a more manual or semi-automated approach, requiring direct interaction by the clinician for the adjustments and measurements [51]. This necessitates a steeper learning curve or greater expertise to ensure accurate measurements. On the other hand, the NSLM leverages computer technology to automate much of the process, enhancing efficiency, reducing the potential for user error, and often providing a more user-friendly experience. It keeps the luminance constant in the central detection field, and the button does not have a limit switch. This absence makes it possible to eliminate clues and avoid increases in fraud during measurement. It was designed to be used binocularly, where the patient looks at a computer screen instead of a test tube, which in turn makes the instrument more practical, facilitating the patient’s interaction with the device [63]. In essence, both CSLM and NSLM serve similar purposes in the assessment of straylight and its impact on visual quality, with NSLM representing an advancement in the technology, offering benefits in terms of efficiency and accuracy [1].

3.4. Compensation Comparison Method

The compensation comparison method is a psychophysical method used in the assessment of straylight, crucial to understand visual disturbances like glare and reduced contrast sensitivity. It involves presenting the subject with a visual stimulus that includes two separate components: one that remains constant and another that fluctuates in intensity [25]. The key objective is to adjust the intensity of the fluctuating component until the observer perceives both components as equally bright, making the method capable of quantifying the degree of light scatter affecting visual perception [64].

3.5. Night Vision Test

The night vision test (NVT) is a method used to evaluate the impact of glare, halos, and other NVDs on visual performance [52]. It consists of a blackboard equipped with an adjustable central light source, surrounded by red LED lights to measure the extent of the light scatter. Participants observe the NVT board and use a laser pointer to outline the perceived shape of the light. From these outlines, a glare score is derived by measuring the distance from each point to the center, providing a quantifiable measure of the impact of glare [52].

3.6. Starlight System

The Starlight System (v.1.0, Novosalud, Valencia, Spain) enables quantitative analysis of light distortion through the use of the disturbance index. The device contains a black screen with a central light (fixation stimulus) and is surrounded by more LEDs in 12 meridians. It calculates the percentage of the visual field obscured due to the central light source [25]. The Starlight software is also mentioned as an additional tool for assessing the quality of scotopic and mesopic vision, especially in multifocal intraocular lens implantations [54]. A study by Pieh et al. [65] measured the diameters of halos using the computer program Glare & Halo (Fitzke FW and C Lohmann, Tomey AG) in patients implanted with multifocal intraocular lenses.

3.7. Gutiérrez Halometer

To assess the effect of halos on night vision, a psychophysical device called a halometer was developed in 2003 [36]. This device enables the precise assessment of the influence of halos on visual perception by generating a disturbance index. Briefly, the halometer consists of two plates inside a methacrylate box. The front of the box has a black cover, also made of methacrylate, with several holes to allow light to escape from the light-emitting diodes (LEDs) located on the plate. The back has guides and holes to isolate the LEDs, and the electronic board is connected to the back of the plates. The subject must stand in front of the device and see a black screen, where the central light source (which also serves as a fixation point) is surrounded by a series of dots distributed over 12 radial lines. In turn, the device is connected to a computer, which processes the data collected during the examination. The task of the subject is to detect the peripheral stimuli while looking at the central bright source. It is very easy to differentiate any point from the (bright) central point. In this equipment, the limit of visibility of the points is determined [36].

3.8. Vision Monitor (Metrovision)

The vision monitor (MonCv3; Metrovision, Pérenchies, France) is a commercial instrument particularly used to measure the size of a halo. It consists of two circular white light sources (LEDs) on each side to generate glare. Each glare source has a unique luminance of 200,000 candelas (cd)/m² and forms a visual angle (φ) of 3.8° from the center of the monitor at a distance of 2.5 m from the observer [53].

3.9. Aston Halometer

This halometer consists of a bright LED in the center, and the test is carried out on a standard mobile tablet, which makes it possible to quantify and analyze the extent of dysphotopsias in different directions of vision. The tablet with a central LED is placed 2 m (m) away in a dark-lit room, and the remote control is via Bluetooth. There is a 1 min adaptation, and the measurement of the eccentricity of the letters equivalent to 0.3 logarithm of the minimum angle of resolution (LogMAR) is achieved by moving the letters themselves more eccentrically from the central LED brightness source in steps of 0.05 degrees (°) until they are first consistently recognized. The eccentricity is noted, and this assessment is repeated in each of the 8 orientations, separated by 45°, to delineate the specific area of glare on a target caused by the halo, measured in degrees [30].

3.10. Rostock Glare Perimeter

This equipment is used to quantify the effects of dysphotopsias under realistic simulated conditions. This method is sensitive and useful in detecting and quantifying age-related glare differences in a healthy population and binocular summation. It also aids in refractive correction procedures and intraocular lens design and, therefore, has potential use in assessing visual quality in patients undergoing refractive or cataract surgery [29].

In short, the subject is placed 3.30 m from a screen that integrates a central cold light source with 2 mm diameter optical fibers. The software produces a black background (with a luminance of less than 0.01 cd/m² projected onto the screen by a projector) and a white marker (with an angular dimension of 0.09 degrees and a luminance of 22 cd/m²), which moves gradually from the periphery to the center. The dot shifts direction unpredictably, moving through one of twelve possible paths. Subjects are required to verbally indicate when they can differentiate the marker’s brightness from that of the light source. Upon making this distinction, the distance from the dot to the central light source is noted. Subsequently, the path of the dot’s movement is randomly altered again [29].

3.11. Halometer: Halo v1.0

The Halometer or Halo v1.0 (Laboratory of Vision Sciences and Applications, University of Granada, Granada, Spain) is a free software that quantifies visual disturbances perceived by detecting a peripheral stimulus around a central main stimulus on the dark background of the monitor [54,55].

Implementing such software in clinical practice results in several advantages, including the simplification of the process, the reliability of the results obtained, and its widespread accessibility, which enables eye care professionals to utilize the software without incurring extra costs. Additionally, it boasts extensive clinical applications, namely the assessment of nocturnal visual performance, monitoring of post-refractive surgery outcomes [66,67], and overseeing the management of ocular diseases [68].

3.12. Light Disturbance Analyzer

Recently, the Physics Center at the University of Minho in Braga, Portugal, developed and introduced a device designed to quantify and characterize optical phenomena, including light distortion, namely, the light disturbance analyzer (LDA, CEORLab, University of Minho, Braga, Portugal). The radiometric characterization [69] and its validation [56] were already described in the literature. The LDA device focuses on characterizing the impact of optical aberrations such as halos, glare, and starbursts that individuals may experience under various lighting conditions, particularly in low-light or nighttime environments. The LDA measures the size, shape, and regularity of these distortions, providing valuable metrics that can help in assessing the optical quality of the eye and the visual disturbances perceived by the patient [34,56].

The hardware consists of a black electronic board with a bright, high-intensity (3000 cd/m²) central light source measuring 5 mm (mm), which acts as a source of glare/disturbance and is therefore responsible for the glare condition. On its periphery are 240 smaller, less intense LEDs (up to 6 cd/m²) of 1 mm each. They are distributed over 24 semi-meridians with a minimum angular separation of 15°, covering an area of 10° at an examination distance of 2 m, and act as stimuli for detecting the limits of glare at different points in the visual field. Their representation and distribution are shown in Figure 3a. Figure 3 (b) and (c) show the central LED switched off and on at the minimum intensity, respectively.

The electronic board is connected to a central control device (laptop), and whenever the subject can identify the light from one of the peripheral LEDs, this feedback is transmitted via a remote response device (laptop mouse). The peripheral stimulus is presented around the central light source in different sequences and semi-meridians and at random times between 250 and 750 milliseconds (ms). Whenever the subject identifies the stimulus, the system presents the next semi-meridian, and the procedure is repeated. In this test, three evaluations are carried out on each semi-meridian. The equipment then determines the average limit of light distortion [56,69].

The software evaluates the following different metrics during the scan:

• Distortion Area (DA): This is the result of the sum of the areas of all the sectors formed between each pair of semi-meridians under analysis and is measured in mm².
• Light Distortion Index (LDI): This is the main parameter and is calculated from the ratio between the area not seen by the subject and the total area explored and is expressed as a percentage. It is indicative of the area that is not visible due to the impairment of light distortion phenomena. Higher LDI values are understood as a lower ability to discriminate small stimuli surrounding the central light source and, therefore, the greater the light disturbance induced by the central light source; Figure 4.
• Best Fit Circle Radius (BFCRad): This corresponds to the radius of the circle that best fits the distortion area, whose value is equal to the average length of the disturbance along each semi-meridian under study, presented in mm.
• Coordinates of the Best Fit Circle (XCoord e YCoord): These are the cartesian coordinates of the center of the screen in degrees.
• Best Fit Circle Center Orientation (BFCOrient): This is the angle of the BFC center from the origin of the coordinates, which corresponds to the center of the screen in degrees.
• BFC Irregularity (BFCIrreg): This is the sum of the deviations between the actual distortion area and the outer perimeter of the BFC along all semi-meridians. It is the sum of the positive and negative values depending on whether the distortion limit is inside or outside the perimeter of the BFC and is measured in mm.
• BFC Irreg Standard Deviation (BFCIrregSD): This is the standard deviation of the BFC Irreg. It determines the degree of asymmetry of the distortion area limited from a perfectly circular shape and is measured in mm. Higher values correspond to more irregular distortion [56].

4. Advantages and Applications of LDA in Clinical Practice

The LDA has certain practical features that can be advantageous in clinical practice, such as having a simplified setup without extra components [69]. The LDA provides various metrics, such as the size, location, and irregularity of visual disturbances, offering information about the patient’s visual condition [69]. This feature proves particularly useful in situations where the optical characteristics are asymmetrical or off-center; Figure 5.

The sensitivity of the LDA to assess light distortion has already been investigated and verified in previous studies (Tables—Supplementary Material) with monofocal, bifocal, and trifocal intraocular lenses [34,71,72], changes in spherical aberration in healthy accommodated and non-accommodated eyes [73], eyes undergoing orthokeratology [74], presbyopes wearing monofocal and multifocal contact lenses [22,70] and pseudophakic individuals [34,72].

A 2016 study by Macedo-de-Araújo et al. [73] evaluated the effect of induced spherical aberration on light distortion. The study included pupil measurements under natural conditions and after pupil dilation and compared the light distortion parameters obtained in the LDA with and without cycloplegia. They concluded that pupil dilation and cycloplegia increased the size of light distortion in healthy eyes, that positive spherical aberration induces more distortion than negative spherical aberration, and, finally, that accommodation and pupil dilation can compensate for the degradation of optical quality induced by spherical aberration. Later, in 2019, Amorim-de-Sousa et al. [28] carried out a study to assess the impact of different levels of positive and negative defocus on luminous disturbance measurements and analyzed how high-order aberrations and topographic quality parameters could influence the perception of photic phenomena. Light distortion was assessed with the LDA in natural accommodative and cycloplegic conditions with a positive and negative induced defocus of 1.00 D. They concluded that both positive and negative induced defocus (uncorrected refractive errors) significantly increased the size of the luminous distortion, but not its irregularity index, and that spherical aberration was associated with the size of the distortion while coma and total aberration were associated with the irregularity of the distortion. In 2023, Martino et al. [75] similarly concluded that under various conditions of optical degradation, including spherical and cylindrical aberrations, and with meticulous control over pupil size, binocular summation was evident. This observation suggests the influence of neural factors. Thus, it implies that apart from the optical attributes, there exists a neural component or adaptation mechanism at play to enhance binocular visual perception.

4.1. Ablative Refractive Surgery and Intraocular Lenses

The key factors that influence visual outcomes after refractive surgery include the ablation zone size, pupil diameter, and optical aberrations like spherical aberration and coma, which impact visual quality, especially under low-light conditions [1,43,58]. A 2022 study using the LDA and QoV questionnaire found post-operative changes in light disturbances following SMILE surgery, with a correlation between the disturbance area and patients’ subjective perception [59]. In another perspective, photic phenomena like halos and glare significantly affect visual quality after multifocal IOL implantation due to light dispersion across different lens zones [76]. LDA studies have shown that monofocal IOLs generally cause less light disturbance than multifocal IOLs, with some improvement in light distortion and visual quality occurring within the first month of post-surgery [77,78,79]. Further research is needed to better understand these phenomena and the adaptation process [18,76].

In the supplementary files, there is a table summarizing the results obtained with the LDA in various studies on intraocular lenses after refractive lens exchange and cataract surgery.

4.2. Applications on Contact Lens

4.2.1. Scleral Lenses

These lenses can improve visual quality for patients with corneal irregularities by masking high-order aberrations. Studies show a reduction in light disturbance with scleral lenses in both regular and irregular corneas [80].

4.2.2. Orthokeratology

This non-surgical method temporarily reshapes the cornea, with studies showing an initial increase in light distortion that stabilizes over time. Pupil size and refractive error are key factors that influence a patient’s visual quality in orthokeratology [74,81,82,83].

4.2.3. Contact Lenses for Presbyopia and Myopia Control

The detailed results obtained with the LDA in studies on contact lenses for presbyopia and myopia control, as well as the effects of defocus and spectacle lenses for myopia control, are provided in the table of supplementary material.

Multifocal contact lenses for presbyopia and myopia control can increase light disturbance, particularly in larger pupils. Dual-focus lenses tend to heighten light distortion initially, but this effect diminishes with binocular use over time [21,22,35,84,85,86].

4.2.4. Changes in Tear Film

Dry eye disease can increase light scattering, resulting in symptoms like halos and visual discomfort [87]. Studies have shown that dry eye, particularly in computer users, worsens a patient’s visual function and increases light disturbances throughout the day [87,88].

5. Conclusions

This work highlights the significant impact of visual quality degradation, particularly under low-light conditions when pupil dilation occurs, which can greatly affect daily activities like nighttime driving and low-light reading. Accurate assessment and quantification of visual disturbances caused by light scattering are crucial for understanding and managing these impairments. Various methods have been developed to address this need, offering both subjective and objective measures that are essential in evaluating the outcomes of ophthalmic interventions such as refractive surgery, intraocular lens implants, and contact lens fittings. These assessment techniques play a vital role in improving patient care by guiding treatment decisions, enhancing post-surgical outcomes, and ultimately contributing to a better quality of life for those affected by visual disturbances. The light disturbance analyzer (LDA) has emerged as a valuable tool for the measurement of visual disturbances, providing precise metrics that support the evaluation of ophthalmic interventions through time.