Analysis of intraocular straylight, especially in relation to age

Subjective Straylight Index: A Visual Test for Retinal Contrast Assessment as a Function of Veiling Glare

Spatial aspects of visual performance are usually evaluated through visual acuity charts and contrast sensitivity (CS) tests. CS tests are generated by vanishing the contrast level of the visual charts. However, the quality of retinal images can be affected by both ocular aberrations and scattering effects and none of those factors are incorporated as parameters in visual tests in clinical practice. We propose a new computational methodology to generate visual acuity charts affected by ocular scattering effects. The generation of glare effects on the visual tests is reached by combining an ocular straylight meter methodology with the Commission Internationale de l'Eclairage's (CIE) general disability glare formula. A new function for retinal contrast assessment is proposed, the subjective straylight function (SSF), which provides the maximum tolerance to the perception of straylight in an observed visual acuity test. Once the SSF is obtained, the subjective straylight index (SSI) is defined as the area under the SSF curve. Results report the normal values of the SSI in a population of 30 young healthy subjects (19 ± 1 years old), a peak centered at SSI = 0.46 of a normal distribution was found. SSI was also evaluated as a function of both spatial and temporal aspects of vision. Ocular wavefront measures revealed a statistical correlation of the SSI with defocus and trefoil terms. In addition, the time recovery (TR) after induced total disability glare and the SSI were related; in particular, the higher the RT, the greater the SSI value for high- and mid-contrast levels of the visual test. No relationships were found for low contrast visual targets. To conclude, a new computational method for retinal contrast assessment as a function of ocular straylight was proposed as a complementary subjective test for visual function performance.

Increased ocular dopamine levels in rabbits after blue light stimulation of the optic nerve head

The purpose was to quantify ocular dopamine in rabbits after stimulation of the optic nerve head with short-wavelength (blue) light to activate melanopsin expressed in the axons of intrinsically photosensitive retinal ganglion cells (ipRGCs). Dopamine levels in tears, aqueous humor, vitreous body, and retina (including choroid) were quantified after blue light stimulation of the optic nerve head of 15 rabbits with an optical fiber for 1 min, 10 min, or no stimulation (n = 5, each group). The left eye of all rabbits was operated on to introduce the optical fiber and stimulate the optic nerve, while the contralateral eye served as internal control. One minute of blue light stimulation significantly increased dopamine concentration in the vitreous body of the treated eyes compared to the contralateral ones (P = 0.015). Stimulation for 10 min significantly increased dopamine concentration in the vitreous body, as well as the aqueous humor (P < 0.05). Therefore, using an optical fiber approach to stimulate the optic nerve head with blue light significantly increased dopamine concentration in the aqueous humor and the vitreous body. This likely reflects an upregulation of retinal dopamine synthesis that could be attributed to ipRGC activation. However, the data provided in this study fell short of establishing a definitive link between dopamine release and ipRGC activation, mainly due to the lack of evidence supporting the expression of the melanopsin photopigment in the optic nerve.

Optical memory effect of excised cataractous human crystalline lenses

Cataracts increase the amount of scattered light in the crystalline lens producing low-contrast retinal images and causing vision impairment. The Optical Memory Effect is a wave correlation of coherent fields, which can enable imaging through scattering media. In this work, we characterize the scattering properties of excised human crystalline lenses by measuring their optical memory effect and other objective scattering parameters, finding the relationship between them. This work has the potential to help fundus imaging techniques through cataracts as well as the non-invasive correction of vision through cataracts.

Effect of Violet Light-Filtering and Manufacturing Improvements in an Extended Depth-of-Focus Intraocular Lens on Visual Performance

Purpose

To assess the experimental visual performance and dysphotopsia characteristics of the new Tecnis Symfony OptiBlue extended-depth-of-focus with violet light-filtering (ZXR00V) intraocular lens (IOL) compared with the colorless Tecnis Symfony (ZXR00) IOL.

Methods

Range of vision was assessed with simulated visual acuity defocus curves, predicted by white light through focus modulation transfer function (MTF) measurements. The clinical visual acuity defocus curve of the ZXR00 IOL was used to validate the predicted range of vision. Image quality was compared by measuring white light MTF at a spatial frequency of 15 cycles per degree (c/deg) for 3 mm and 5 mm pupil diameters with optical powers of 5 D, 20 D, and 34 D using the average corneal eye (ACE) model with the average spherical and chromatic aberration of the cataract population. Effects on dysphotopsias were predicted by measurement and computer simulation of light scatter (straylight parameter) and subsequent determination of retinal veiling luminance (RVL) in vitro. Contrast enhancement under challenging light conditions was calculated based on the effects in RVL.

Results

The simulated visual acuity defocus curves and image quality outcomes were comparable between the ZXR00V and ZXR00 IOLs. The area under the straylight curve for the straylight parameter showed a 19% improvement in halo performance with ZXR00V versus ZXR00. A 12% to 17% reduction in RVL was achieved in favor of ZXR00V over ZXR00, which enhanced contrast vision by 9% to 13% under challenging light conditions.

Conclusion

The violet light-filtering technology and improved manufacturing of ZXR00V delivers a comparable range of vision and tolerance to refractive error to ZXR00 while mitigating dysphotopsias and enhancing contrast vision.

Light scattering from a diffractive-refractive intraocular lens: a goniometer-based approach for individual zone assessment

We proposed and tested a method to measure light scattering from the diffractive lens profile in an echelle element featuring 9 zones. Measurements were performed using a goniometer-based setup up to 7.5°. The proportion of scattered light was calculated to derive the loss of light. Material scattering was minimal (∼1 deg²/sr); however, each echelle zone acted as a scattering source. A nearly gradual straylight increase was found with the zone number showing peak intensity between 3° and 3.75°. An estimated 6.2% ± 0.1% was lost due to scattering, which ought to be considered when reporting an IOL's light loss.

Photophobia and disability glare in adult patients with Marfan syndrome: a case-control study

PURPOSE

The aim of the present study was to investigate photophobia and disability glare in adult patients with Marfan syndrome (MFS).

METHODS

In this case-control study, 44 patients with MFS (87 eyes) were compared to 44 controls (88 eyes), who were matched for age and sex. The subjects were asked to grade their photophobia and glare using 10-cm visual analogue scales (VAS), which were marked with 'never' at zero and 'always' at 10 -cm. In addition, disability glare was measured with C-Quant straylight meter.

RESULTS

The patients with MFS had significantly higher VAS scores than the controls in four out of seven statements related to photophobia and glare. When including cataract, spherical equivalent, iris colour, axial length and corneal curvature, three of the seven statements were still significantly different between the two groups. The mean straylight values were 1.29 ± 0.03 log(s) in the MFS group and 1.01 ± 0.03 log(s) in the control group (p < 0.001, mixed model). These differences remained significant after adjusting for cataract, spherical equivalent, iris colour, axial length and corneal curvature.

CONCLUSION

Patients with MFS reported more photophobia and had a higher straylight value than the control group. Awareness of these findings of more photophobia and glare in the MFS patients is important when counselling and treating these patients.

Optical instrument for the study of time recovery from total disability glare vision

Disability glare is defined as the loss of contrast sensitivity of the retinal image due to intraocular straylight originated from the presence of an intense and broad bright light in the field of vision. This loss of vision can range between vision loss at high spatial frequencies or total temporal blindness. If the extreme case occurs, the recovery time is crucial in night driving conditions or those professional activities in which maximum visual acuity is required at any moment. The recovery time depends mainly on the intensity and glare angle of the light source, ocular straylight, and the photoreceptor response at the retina. The recovery time can also be affected by ocular pathologies, aging, or physiological factors that increase ocular straylight. The aim of this work is to develop a new optical instrument based on psychophysical methodology as well as to investigate the recovery time from total disability glare (photobleaching) as a function of the contrast of the visual target and the glare angle of the source in healthy volunteers. Results showed significant exponential correlation between recovery time and contrast of the visual target and linear correlation between contrast sensitivity and the glare angle. Those findings allowed to obtain an empirical expression to compute the recovery time required to restore contrast sensitivity baseline vision after photobleaching. Finally, a statistical dependence of recovery time with age was found for short glare angles that disappear as the glare angle increases.

Short-Term Peripheral Contrast Reduction Affects Central Chromatic and Achromatic Contrast Sensitivity

Peripheral retinal contrast reduction is suggested as a potential myopia control strategy. However, the underlying mechanism is yet unknown. Therefore, this study investigated the influence of peripheral contrast reduction on central chromatic and achromatic contrast sensitivity (CS). A total of 19 participants were included. Peripheral contrast reduction was induced via Bangerter foils of 0.4 and 0.8 density, each with a clear central zone of 8.0 mm diameter. Central achromatic and chromatic (for S-, M-, and L-cone types) CS was measured at 3 and 12 cpd in a 2-IFC psychophysical procedure. CS was tested monocularly at 0, 30, and 90 min of adaptation time, while the fellow eye was covered by an infrared filter. With the filter in place, pupil size was controlled to be smaller than the clear central aperture. Data were analyzed using linear mixed models. Cone-type CS showed significant differences among each other (all p < 0.05), except for the achromatic and L-cone type (p = 0.87). The minimum sensitivity was found with the S-cone type and the maximum with the M-cone type. Central achromatic and chromatic CS were equally affected by diffusion. The level of peripheral diffusion also influenced CS, while the 0.8 Bangerter foil led to a higher reduction in CS compared to the 0.4 Bangerter foil (p = 0.0008) and the control condition (p = 0.05). A significant reduction in CS occurred between 30 and 90 min of adaptation time (p < 0.0001). The current study found that peripheral contrast reduction impacted central achromatic and chromatic CS equally. It further showed that the amplitude of reduction was influenced by the level of diffusion, with the reduction becoming more pronounced over time.

Implementation of the Frequency Scatter Index in Clinical Commercially Available Double-pass Systems

A previous work has reported a methodology to quantify intraocular scattering using a high sensitivity double-pass instrument with a robust index, the frequency scatter index. The purpose of our study was to evaluate an adaptation of the frequency scatter index for use in clinical double-pass systems. A prospective observational study was carried out in a group of patients with nuclear cataracts (n = 52) and in a control group (n = 11) using conventional double-pass systems. The frequency scatter index and the objective scatter index were used to assess the scattering. The Spearman coefficient was calculated to assess the correlation between both indexes, obtained from the double-pass images. Simultaneous measurements were performed with a double-pass and with a Hartmann-Shack wavefront sensor in the control group. The root-mean-square wavefront error and the full width at half maximum of the double-pass image were used to quantify the residual aberrations introduced by the variations in pupil size and retinal eccentricity. Measurement in eyes with different grades of cataracts shows a strong correlation (ρ = 0.929, p < .0001) between the frequency scatter index and the objective scatter index. A certain degree of correlation was observed between the objective scatter index and the root-mean-square and between the objective scatter index and the full width at half maximum, both for measurements with a different pupillary diameter and with a different retinal eccentricity (p < .05). No relationship was observed between the frequency scatter index and the root-mean-square or between the frequency scatter index and the full width at half maximum (p > .05). We have introduced and evaluated an adaptation of a methodology proposed recently for the measurement of intraocular scattering using the double-pass technique with a robust index, which is less affected by ocular aberrations. The frequency scatter index can be applied to conventional double-pass instruments available in clinical environments.

Glare and Mobility Performance in Glaucoma: A Pilot Study

PRCIS

Glare disability affects patients with moderate and severe glaucoma. Under glare conditions, mobility performances of glaucoma patients are reduced.

PURPOSE

The aim of this study was to evaluate glare disability and its impact on mobility and orientation in glaucoma patients.

METHODS

Twenty-two glaucoma patients and 12 age-matched control subjects were included. All patients underwent a clinical evaluation of visual function and halo size measurements to determine glare disability with a glare score (GS) of the best eye and worse eye. Mobility was evaluated by 4 mobility courses on an artificial street (StreetLab) under photopic conditions (P) and mesopic conditions with an additional light source in front of the patient to mimic dazzling conditions (M+G). Mobility time, mobility incidents, trajectory segmentation, distance traveled, preferred walking speed on trial (WS) and percentage of preferred walking speed (PPWS) were recorded, and the Nasa task load index (Nasa-TLX) was evaluated.

RESULTS

GS of the worse eye and GS of the best eye were significantly higher in glaucoma patients than in the control group (P=0.001 and 0.003). It was significantly different between moderate glaucoma patients and controls (P=0.001 and 0.010, respectively) and between severe glaucoma patients and controls (P=0.049 and 0.016). In locomotion tasks, comparing performance under M+G and P conditions, mobility performance was significantly different concerning mobility time (P=0.010), distance traveled (P=0.008), WS (P=0.007), PPWS (P=0.006), and Nasa-TLX (P=0.017) in the glaucoma group. Under M+G lighting conditions, mobility performance for glaucoma patients was significantly worse than controls with regard to WS (P=0.038), PPWS (P=0.0498), mobility time (P=0.046), and Nasa-TLX (P=0.006).

CONCLUSION

Glare disability was observed in patients with moderate and severe glaucoma and had an impact on their mobility performance.

Visualization of Forward Light Scatter in Opacified Intraocular Lenses and Straylight Assessment

Background: Qualitative visualization of forward light scatter and quantitative straylight measurement of intraocular lenses (IOLs). Methods: We analyzed two calcified IOL-explants, the Euromaxx ALI313Y (Argonoptics GmbH) and the LS-312 MF30 (Oculentis BV), one IOL with artificially induced glistenings (PC-60AD, Hoya), and one control (CT Asphina 409MP, Carl Zeiss Meditec AG) free of any opacification. Analysis included light microscopy, qualitative light scatter visualization using ray propagation imaging technique, and quantitative straylight measurement using C-Quant (Oculus). Results: More light scattering effect—visible as increased light intensity outside the IOL’s main focus—was evident in all opacified IOLs than the control. The highest straylight levels were observed in the Euromaxx (289.71 deg²/sr), which showed extensive granular deposits throughout its optic, followed by the MF30 (78.58 deg²/sr), which only showed opacification in its center. The glistenings-IOL demonstrated numerous microvacuoles within the optic and had straylight levels of 22.6 deg²/sr, while the control showed the lowest straylight levels (1.7 deg²/sr). Conclusions: Ray propagation imaging technique allowed qualitative assessment of off-axis veils of light that result from increased forward light scattering. Straylight was increased in all opacified lenses compared to the clear control lens. The IOL opacifications are significant sources of glare.

Intraocular Scattering, Blinking Rate, and Tear Film Osmolarity After Exposure to Environmental Stress

Purpose

Dry environments, such as those in offices or aircraft cabins, can potentially generate ocular discomfort and alter the tear film. We compare light scatter, blinking rate, and tear osmolarity in young and older subjects after exposure to low humidity using a controlled environmental chamber.

Methods

Two groups of healthy subjects were recruited; younger (N = 13, 27 ± 6 years) and older (N = 23, 71 ± 7 years). Measurements were carried out before and after 90-minute exposure to low relative humidity (5%) and constant temperature (23 degrees). Ocular light scatter was measured using a double-pass instrument (OQAS, Visiometrics, Spain). Blinking rate was monitored using an infrared video camera. Tear osmolarity was measured using the TearLab system (Escondido, CA, USA).

Results

Ocular light scatter increased by a factor of 10% after exposure to low humidity in the older group (P = 0.03) but did not change significantly in the younger group. Blinking rate increased significantly (40% more blinks) in both groups but there was no difference between the groups. No significant differences in osmolarity were shown between two age groups or as result of environmental stress.

Conclusions

Exposure to dry environment increased light scatter in older subjects. Although more blinks were triggered in both younger and older groups to prevent corneal dehydration, there was no difference between the groups. Blink rate and osmolarity are not associated with the difference in light scatter.

Translational Relevance

Our work approaches a clinical care problem using basic research methods (measuring ocular scatter and blink ratio).

Visual Adaptation to Scattering in Myopes

Myopes exhibit a larger capability of adaptation to defocus. Adaptation produces a boost in visual performance that can be characterized through different metrics. The ability of myopes to adapt to other sources of blur, such as diffusion, has not been studied so far. In this work, a group of 20 myopes with normal vision underwent high-contrast visual acuity (VA) measurements under different viewing conditions, wearing their refractive correction with or without a diffuser (Bangerter filter, BF). VA decreased immediately after wearing the BF of density 0.6, showing a significant relationship with the ocular refraction. After 40 minutes of binocular vision through the BF, a statistically significant increase (p = 0.02) in VA from 0.54 to 0.62 in decimal scale (from 0.3 to 0.2 logMAR) was obtained. No correlation with the refraction was observed. After removing the diffuser, VA returned to baseline. A control group (17 subjects) underwent the same experimental protocol but without diffuser filters. No significant changes in VA were found in this group. We describe a new type of contrast adaptation to blur in myopes caused by scattering, rather than by defocus. The effects of low scattering levels in vision might be relevant in the analysis of early stage of cataract, amblyopia treatments, and myopia understanding.

Laboratory evaluation of higher-order aberrations and light scattering in explanted opacified intraocular lenses

Background

Intraocular lens (IOL) calcification is a serious condition that can only be treated by removing the clouded lens. Since explantation bears the risk of complications, it is often deferred until the patient finds the symptoms intolerable. Usually, as the IOL opacifies, visual acuity is minimally affected early on. In this study, we assessed the impact of IOL opacification on optical quality.

Methods

We analyzed ten opacified explanted IOLs (Oculentis GmbH). Wavefront aberrations were obtained with a SHSOphthalmic device (Optocraft GmbH), which features a Hartmann-Shack sensor. The root mean square (RMS) of higher-order aberrations (HOAs) was compared. The effect of calcification on image quality was assessed through the Strehl ratio (SR). We detected light scattering with a C-Quant (Oculus GmbH) and expressed it as a straylight parameter.

Results

At 2 mm, 3 mm and 4 mm, the mean RMS (±standard deviation) was 0.033 μm (±0.026 μm), 0.044 μm (±0.027), and 0.087 μm (±0.049), respectively. The mean SR value was 0.81 ± 0.15 at 3 mm, with four IOLs showing a nearly diffraction-limited performance, but in two explants, opacification precluded reliable measurements. Increased straylight was found in all opacified IOLs with a mean value of 150.2 ± 56.3 deg²/sr at 3 mm.

Conclusions

We demonstrated that IOL opacification induces HOAs. However, the RMS remained low, which resulted only in a slight reduction of the SR-derived optical quality. On the other hand, we found a severe straylight elevation in the opacified lenses, which may result in dysphotopsia, such as glare, and subjective complaints, despite good visual acuity.

Iterative-Trained Semi-Blind Deconvolution Algorithm to Compensate Straylight in Retinal Images

The optical quality of an image depends on both the optical properties of the imaging system and the physical properties of the medium in which the light travels from the object to the final imaging sensor. The analysis of the point spread function of the optical system is an objective way to quantify the image degradation. In retinal imaging, the presence of corneal or cristalline lens opacifications spread the light at wide angular distributions. If the mathematical operator that degrades the image is known, the image can be restored through deconvolution methods. In the particular case of retinal imaging, this operator may be unknown (or partially) due to the presence of cataracts, corneal edema, or vitreous opacification. In those cases, blind deconvolution theory provides useful results to restore important spatial information of the image. In this work, a new semi-blind deconvolution method has been developed by training an iterative process with the Glare Spread Function kernel based on the Richardson-Lucy deconvolution algorithm to compensate a veiling glare effect in retinal images due to intraocular straylight. The method was first tested with simulated retinal images generated from a straylight eye model and applied to a real retinal image dataset composed of healthy subjects and patients with glaucoma and diabetic retinopathy. Results showed the capacity of the algorithm to detect and compensate the veiling glare degradation and improving the image sharpness up to 1000% in the case of healthy subjects and up to 700% in the pathological retinal images. This image quality improvement allows performing image segmentation processing with restored hidden spatial information after deconvolution.

Quantification of the In Vitro Predisposition to Glistening Formation in One Manufacturer's Acrylic Intraocular Lenses Made in Different Decades

Introduction

Foldable hydrophobic acrylic intraocular lenses (IOLs) are prone to develop a long-term postoperative material change called glistenings. The aim of this study was to investigate the changes in the predisposition for glistening formation in one type of hydrophobic acrylic IOL material from its introduction to the present day.

Methods

In a laboratory setup, an in vitro model was used to induce glistenings in hydrophobic acrylic IOLs manufactured by one company (Alcon, Fort Worth, TX, USA) in different years: 23 1990s-manufacture hydrophobic acrylic three-piece IOLs (MA30BA/MA60AC) that were explanted in 1996 and 1997, and five of each of the newer AcrySof IOL models (MA60AC, SA60AT, TFNT00 and SN60WF) from 2014 to 2017. Furthermore, five Clareon (SY60WF) IOLs were put through the same accelerated aging procedure. The number of microvacuoles per square millimeter (MV/mm²) was determined in the central part of each IOL optic and compared between the groups.

Results

The mean number of MV was highest in the 1990s-manufacture Alcon acrylic IOLs, with 1289 (± 738) MV/mm². The number decreased to 650 (± 101), 192 (± 105), 175 (± 112) and 47 (± 26) for MA60AC, SA60AT, TFNT00 and SN60WF, respectively. The lowest count was obtained in the Clareon group, with 1 (± 1) MV/mm².

Conclusions

A high number of glistenings was induced in the explanted IOLs from the 1990s. The propensity for glistening formation decreased considerably after that decade and now in current use. Even though in vitro glistening formation in today’s AcrySof material was low, the Clareon material was essentially glistenings-free.

Straylight in Different Types of Intraocular Lenses

Purpose

To show the importance of measuring the angular distribution of straylight as an in vitro test for intraocular lenses (IOLs).

Methods

The optical integration method was implemented to measure the point spread function, up to 5.1°, of IOLs immersed in a wet cell. The straylight parameter was calculated as the product of the point spread function by the squared angle. The effect of the scattered light is shown in extended images of a target surrounded by headlamps as glare sources. Three different IOLs were tested: (1) AcrySof IQ SN60WF, monofocal, (2) AcrySof IQ PanOptix, trifocal, and (3) Tecnis Symfony ZRX00, bifocal with extended depth of focus. Measurements were compared to previously reported clinical studies where the same IOL models were implanted.

Results

The mean amount of scattered light, between 1.0° and 5.1°, generated by each IOLs were, in deg²sr^{- 1} units: (1) 1.2, (2) 12.1, and (3) 33.4. Lens (3) present a high amount of straylight related to a halo of an approximate diameter of 2°.

Conclusions

In vitro measurements of the angular distribution of the point spread function of different types of IOLs showed important aspects related to their manufacturing quality. These results are in line with previous clinical findings where glare sensitivity was tested in the same angular range.

Translational Relevance

In vitro measurement of angular dependence of straylight in IOLs, regardless their design, provides a valuable feedback to improve their optical quality. The minimization of the amounts of straylight positively impacts the recurrence of photic phenomena.

The Influence of the Stimulus Design on the Harmonic Components of the Steady-State Visual Evoked Potential

Steady-state visual evoked potentials (ssVEPs) are commonly used for functional objective diagnostics. In general, the main response at the stimulation frequency is used. However, some studies reported the main response at the second harmonic of the stimulation frequency. The aim of our study was to analyze the influence of the stimulus design on the harmonic components of ssVEPs. We studied 22 subjects (8 males, mean age ± SD = 27 ± 4.8 years) using a circular layout (r₁ = 0–1.6°, r₂ = 1.6–3.5°, r₃ = 3.5–6.4°, r₄ = 6.4–10.9°, and r₅ = 10.9–18°). At a given eccentricity, the stimulus was presented according to a 7.5 Hz square wave with 50% duty cycle. To analyze the influence of the stimulus eccentricity, a background luminance of 30 cd/m² was added to suppress foveal stray light effects; to analyze the influence of simultaneous foveal and peripheral stimulations, stimulations are performed without stray light suppression. For statistical analysis, medians M of the amplitude ratios for amplitudes at the second harmonic to the first harmonic and the probability of the occurrence of the main response at the second harmonic P(MCSH) are calculated. For stimulations with foveal stray light suppression, the medians were M_0–1.6° = 0.45, M_1.6–3.5° = 0.45, M_3.5–6.4° = 0.76, M_6.4–10.9° = 0.72, and M_10.9–18° = 0.48, and the probabilities were P_0–1.6°(MCSH) = 0.05, P_1.6–3.5°(MCSH) = 0.05, P_3.5–6.4°(MCSH) = 0.32, P_6.4–10.9°(MCSH) = 0.29, and P_10.9–18°(MCSH) = 0.30. For stimulations without foveal stray light suppression, the medians M were M_0–1.6° = 0.29, M_1.6–3.5° = 0.37, M_3.5–6.4° = 0.98, M_6.4–10.9° = 1.08, and M_10.9–18° = 1.24, and the probabilities were P_0–1.6°(MCSH) = 0.09, P_1.6–3.5°(MCSH) = 0.05, P_3.5–6.4°(MCSH) = 0.50, P_6.4–10.9°(MCSH) = 0.55, and P_10.9–18°(MCSH) = 0.55. In conclusion, the stimulus design has an influence on the harmonic components of ssVEPs. An increase in stimulation eccentricity during extrafoveal stimulation leads to a transition of the main response to the second harmonic. The effect is enhanced by a simultaneous foveal stimulation.

Contrast sensitivity and retinal straylight after alcohol consumption: effects on driving performance

In this study, we aimed to investigate the effects of alcohol intake on visual function and driving performance, as well as on the relationship between these. A total of 40 healthy participants took part in three experimental sessions: one baseline session and two further sessions after consuming two different quantities of alcohol (300 ml and 450 ml of red wine). The breath alcohol content (BrAC) was measured using a breath analyzer. The contrast sensitivity and retinal straylight due to the forward intraocular scattering were measured to characterize visual function, and driving performance was assessed in three different scenarios using a driving simulator. The results showed a deterioration in contrast sensitivity and retinal straylight after drinking alcohol, in addition to an impaired ability to drive, especially for the highest alcohol intake. We also observed that the deteriorated driving performance was a function of the contrast sensitivity and retinal straylight under the effects of alcohol, indicating that these visual variables can partially predict driving performance in these conditions.

Combining optical and neural components in physiological visual image quality metrics as functions of luminance and age

Visual image quality metrics combine comprehensive descriptions of ocular optics (from wavefront error) with a measure of the neural processing of the visual system (neural contrast sensitivity). To improve the ability of these metrics to track real-world changes in visual performance and to investigate the roles and interactions of those optical and neural components in foveal visual image quality as functions of age and target luminance, models of neural contrast sensitivity were constructed from the literature as functions of (1) retinal illuminance (Trolands, td), and (2) retinal illuminance and age. These models were then incorporated into calculation of the visual Strehl ratio (VSX). Best-corrected VSX values were determined at physiological pupil sizes over target luminances of 104 to 10-3 cd/m2 for 146 eyes spanning six decades of age. Optical and neural components of the metrics interact and contribute to visual image quality in three ways. At target luminances resulting in >900 td at physiological pupil size, neural processing is constant, and only aberrations (that change as pupil size changes with luminance) affect the metric. At low mesopic luminances below where pupil size asymptotes to maximum, optics are constant (maximum pupil), and only the neural component changes with luminance. Between these two levels, both optical and neural components of the metrics are affected by changes in target luminance. The model that accounted for both retinal illuminance and age allowed VSX, termed VSX(td,a), to best track visual acuity trends (measured at 160 and 200 cd/m2) as a function of age (20s through 70s) from the literature. Best-corrected VSX(td,a) decreased by 2.24 log units between maximum and minimum target luminances in the youngest eyes and by 2.58 log units in the oldest. The decrease due to age was more gradual at high target luminances (0.70 log units) and more pronounced as target luminance decreased (1.04 log units).

Visual Function and Functional Decline in Patients With Waterclefts

Purpose

To investigate visual function in eyes with three subtypes of waterclefts (WCs).

Methods

Of patients in Kanazawa Medical University Hospital (2013-2017) and participants of Monzen Eye Study (2013-2016), 77 transparent lenses, mean age 66.7 years, and 70 eyes with only WC opacity of 70 patients, mean age 68.1 years, divided into peripheral-, central-, and total-type WC groups, were analyzed. Opacity was classified by one ophthalmologist using slit-lamp microscopy. Corrected-distance visual acuity (CDVA), contrast visual acuity (CVA), spherical equivalent (SE), astigmatism values, corneal refractive power (CP), axial length (AL), straylight, backward light scattering (BLS), and higher order aberrations (HOA) were measured and lenticular refractive power (LP) was calculated based on the values of AL, CP, and SE.

Results

Central-type WC showed significant decrease in CDVA and CVA and increase in straylight compared with control. Total-type WC showed significant decreases in CDVA, CVA, and LP, and increase in straylight, compared with control and peripheral-type WC. Total- and central-type WCs had significantly higher ocular total HOA and total-type WC had significantly higher internal total HOA than control. HOA correlated positively with CDVA (P < 0.001) and straylight (P = 0.020), and CDVA negatively with straylight in eyes with WCs (P = 0.008).

Conclusions

Total-type WC was associated with decreased LP, causing hyperopia, decreased CDVA and higher straylight; thus, such lenticular change should be considered for surgery indication. Significant correlations between HOA and both CDVA and straylight suggested increased HOA may decrease visual function in eyes with WCs.

Light scattering levels from intraocular lenses extracted from donor eyes

PURPOSE

To assess light scatter levels of intraocular lenses (IOLs) extracted from donor eyes to understand straylight elevation documented earlier in pseudophakic population studies and identify potential sources of light scattering in IOLs.

SETTING

Rotterdam Ophthalmic Institute, Rotterdam, the Netherlands.

DESIGN

Experimental study.

METHODS

Light scattering in 74 donor IOLs was measured with the C-Quant device adapted for in vitro analysis of IOLs. Straylight was assessed at a 2.5-degree and 7.0-degree scatter angle, and results were compared with the straylight of a 20-year-old crystalline lens, a 70-year-old crystalline lens, and a lens with cataract. To identify potential changes to the IOL material, the IOLs were examined with a light microscope and a slitlamp.

RESULTS

At 2.5 degrees and 7.0 degrees, the straylight parameter was 5.78 deg²/steradian (sr) ± 4.70 (SD) and 5.06 ± 4.01 deg²/sr, respectively. Forty-one percent of IOLs showed lower straylight than the 20-year-old lens. In 14%, the scattering intensity was higher than in the 70-year-old lens; none showed straylight comparable to that of the cataractous lens. Increased straylight was associated with surface deposits, snowflake-like degeneration, and glistenings. The incidence of IOL-related complications differed between the IOL groups.

CONCLUSIONS

Microscopic structural alterations of IOLs play a major role in straylight elevations in pseudophakic eyes. A clear correlation with degeneration and/or alteration of implanted IOLs was found. Although these IOL-related complications would likely not affect visual acuity, they give rise to straylight and thus can cause disability glare and other symptoms.

Straylight As The Result Of Refractive Correction

Purpose

To investigate the effect of refractive correction on straylight.

Patients and methods

Straylight values were measured with the C-Quant (Oculus Optikgeräte, GmbH, Wetzlar, Germany) in 1) near-emmetropic eyes (n=30) with various negative powered refractive lenses and in 2) myopic eyes (n=30) corrected with prescribed eyeglasses and contact lenses. The straylight measurements in each group were compared in the different conditions.

Results

In the near-emmetropic group, a significant effect (p<0.001) of each added negative diopter was found to increase straylight values with 0.006 log-units. In the second group, no significant correlation with type of correcting lens was found on straylight values.

Conclusion

Refractive correction with high minus power (contact) lenses result in subtle increase of straylight values. These changes are relatively small and do not lead to visual disability in a clinical setting.

Fluctuation in straylight measurements during the visual recovery phase after small incision lenticule extraction

PURPOSE

To investigate the postoperative straylight changes during the visual recovery phase after small incision lenticule extraction (SMILE) and their association.

METHODS

Seventy consecutive eyes from 37 patients with a mean age of 30.92 ± 7.26 years and a mean preoperative spherical equivalent of -5.24 ± 1.90 dioptres undergoing myopic or myopic astigmatism SMILE correction were included in this prospective study. Patients were followed up at days 1, 3, 7, 14, 21 and 28 after standard SMILE. Straylight was measured using the C-Quant straylight meter (Oculus GmbH, Germany) preoperatively and at each postoperative visit.

RESULTS

Preoperatively, the mean straylight measurement was 1.16 ± 0.16. After SMILE, the mean straylight values were 1.12 ± 0.14 and 1.13 ± 0.13 at days 7 and 14, which were significantly reduced compared to preoperative values (p ≤ 0.028). Straylight returned to baseline by week 3 (p = 0.160) and remained stable onwards (p = 0.651). A lower ablation ratio was associated with less straylight level at days 1, 3, 14 and 21 (p ≤ 0.0497) in the multivariable regression model. Likewise, better visual acuity was associated with lower straylight at days 7, 14 and 28 postoperatively (p ≤ 0.038). A small proportion of eyes (range: 0-12.86%) had ≥0.30 log(s) increase in postoperative straylight within the first month after SMILE.

CONCLUSIONS

SMILE induced a temporary decrease in straylight. It gradually returned to the preoperative level, which could be related to a number of dynamic processes during corneal healing. In the small proportion of patients with an increase in straylight postoperatively, this can affect their visual recovery during the early postoperative period.

Objective measurement of forward-scattered light in the human eye: An electrophysiological approach

PURPOSE

Psychophysical measurements are used to examine the perception of ocular stray light, for example, with C-Quant. These measurements are subjective due to their principles. This work aims to determine ocular stray light objectively; thus, a psychophysical method is transferred into an electrophysiological setup.

METHODS

Stray light perception was measured using steady-state visual evoked potentials (VEPs) in 10 healthy subjects (7 males, 3 females, mean age ± SD: 29.6 ± 4.1 years). Stray light emulating filters (Tiffen Black Pro Mist 2) were used for simulating the effect of cataracts to validate the results for increased scattered light conditions. Based on the direct compensation method, the stimulus consisted of a central test field (radius = 2°) with a luminance adjustable compensation light and surrounding ring-shaped stray light source (radius = 5 to 10°). Both flickered in the counter phase at a frequency of 7.5 Hz. The stimuli were presented for 15 luminance levels of the compensation light. The recorded steady-state VEPs at Oz channel were transformed by means of Fourier analysis. The magnitudes at the evoked frequency were plotted against the measured brightness levels of the compensation light. By fitting two linear functions to the resulting data points, a robust minimum log(Leq) was determined, which was correlated with the amount of stray light perception. We measured the stray light parameter log(sc) using C-Quant. For comparison, our results were converted into the C-Quant equivalent parameter log(sepm) and paired t-tests were performed for normal distributed results.

RESULTS

A significant difference is observed between log(sepm) (without filter) and log(sepm) (with BPM 2 Filter) (p>0.05). No significant difference is observed between log(sepm) (without filter) and log(sc) (without filter) (p > 0.05) and between log(sepm) (with BPM 2 filter) and log(sc) (with BPM 2 filter) (p > 0.05).

CONCLUSION

The electrophysiological approach offers the ability to measure stray light perception in an objective manner.

Glistening Formation and Light Scattering in Six Hydrophobic-Acrylic Intraocular Lenses

PURPOSE

To study the glistening formation in various hydrophobic-acrylic intraocular lens (IOL) models, and to evaluate the effect of glistenings on light scattering in these IOLs.

DESIGN

Laboratory investigation.

METHODS

The susceptibility of the hydrophobic-acrylic material to develop glistenings was evaluated in 6 IOL models. Accelerated lens aging was induced by immersing the IOLs in a solution at 45 C for 24 hours and cooled to 37 C for 2.5 hours. Light microscopy and image acquisition were performed. Glistening statistics-that is, microvacuoles' (MV) number and size-were derived from image analysis. Light scattering was measured using a clinical device featuring an adaptation for in vitro IOL assessment.

RESULTS

The number of glistenings differed among the studied IOLs and ranged from 0 to 3532 MV/mm². In 1 model, glistenings were found only at the periphery, with diffuse light scattering observed centrally despite the absence of microvacuoles. The mean size of glistenings ranged from 5.2 to 10.2 μm. The mean straylight parameter of the IOLs increased from 0.6 to 5.0 deg²/sr after accelerated aging. Straylight elevation demonstrated a proportional relationship with the glistening number.

CONCLUSIONS

We showed that hydrophobic-acrylic lenses differ in their resistance to glistenings, as one group proved to be glistening-free, but the other models revealed varying grades of glistenings. Moreover, we demonstrated that the presence of glistenings results in increased straylight, and that straylight proportionally depends on the glistenings number irrespective of the IOL model. However, more research is needed to confirm that the relationship we found holds for all hydrophobic-acrylic IOLs.

Influence of age and spectral power distribution on mesopic visual sensitivity

The ability of the human visual system to detect stimuli at low illumination levels provides awareness of potential risks. The influence of age and spectral power distribution on mesopic spectral sensitivity is analyzed. Two typical light sources are used, a high-pressure sodium lamp (HPS), with a higher content of long wavelengths, and a metal halide lamp (MH), with a higher content of short wavelengths. Two experiments were performed, using a two-channel Maxwellian-view optical system to measure contrast threshold under different experimental conditions. In Experiment 1, three age groups (young, middle-aged and old, n = 2 each), two retinal locations (on-axis and off-axis vision), four background luminances (0.01, 0.07, 0.45, and 3.2 cd/m²), and two photometry systems (photopic and the MES2 systems) were considered. In Experiment 2, contrast threshold measurement was performed with two age groups (young and old, n = 11 each), one retinal location (off-axis vision), one background luminance (0.01 cd/m²), and two photometry systems (photopic and the MES2 systems). In on-axis vision, neither age nor spectral power distribution have an effect on the contrast threshold. In off-axis vision, however, a significant interaction between age and spectral power distribution is obtained, albeit only at 0.01 cd/m² with an MH lamp. Only at this lowest background luminance was the greater content of short wavelengths of this lamp responsible for higher rod stimulation in off-axis vision, with the subsequent improvement in detection performance in young subjects. However, the effect of diffused light inside the aged eye counteracted the benefits of increased rod sensitivity for the MH lamp.

Long-Term Changes in Straylight Induced by Overnight Orthokeratology: An Objective Measure Using the Double-Pass System

Purpose: To map the time course of changes in intraocular straylight of the human eye 1 year after initial lens wearing for orthokeratology treatment using the objective double-pass technique. Materials and Methods: A total of 35 subjects (19 males and 16 females) completed the study. The mean age was 11.46 ± 2.33 years (range, 8-16 years). All subjects were fitted with spherical four-zone orthokeratology lenses following the procedures recommended by the lens manufacturer. The subjects were required to wear the lens for at least eight consecutive hours at night. After lens removal during the daytime, objective scattering index (OSI) was evaluated using the double-pass technique (OQAS-II, Visiometrics, Terrassa, Spain) prior to lens dispatch (baseline), followed by evaluations at 1 week, 1 month, 6 months, and 12 months after the initial lens wearing. Longitudinal changes were fitted to a model containing both an impairing and recovery component, and the results were based on an extrapolation between the visits. Results: OSI rose quickly following lens wearing, reaching its highest level (double that of baseline values) by approximately 1.47 months. However, the recovery phase was slow and modest. One year after the initial lens wearing, OSI exhibited a 20% recovery from the peak level, but remained 63% higher than the baseline level. Conclusions: Intraocular straylight immediately increased flowing lens wearing, and this change reaches maximal level around 1 month after lens wearing. Slow but significant recoveries of optical quality subsequently followed.

The significance of changes in pupil size during straylight measurement and with varying environmental illuminance

PURPOSE

In this work, we investigated the pupillary conditions during straylight measurement, and the potential effect this might have on the measured straylight.

METHODS

Five young (26-29-years-old) and 15 older (50-68-years-old) individuals participated in this study. First, the pupil diameter of both eyes was measured at three room illuminances. Next, straylight was assessed at two room illuminances. Simultaneously, the change in pupil size of the fellow eye was registered by a camera.

RESULTS

Pupil size decreased with room illuminance and with age (both p<0.05). The dependency of pupil size on age decreased as room illuminance increased (0.018mm/year at 4 lux, 0.014mm/year at 40 lux, and 0.008mm/year at 400 lux illuminances). However, during straylight measurement, pupil sizes hardly differed between 4 and 40 lux illuminances. Respective pupil sizes corresponded with 399 and 451 lux adaptation on average. No statistically significant difference was found between the straylight under the two illuminances with average R2=0.85, p<0.05.

CONCLUSION

We conclude that the illuminance of the examination room during straylight assessment does not affect the outcome in normal eyes. In fact, under mesopic and scotopic conditions, the luminance of the test field is so much higher than that of the room so that it determines the pupil size. Regardless of the lighting level, straylight measured in a laboratory, is valid for photopic pupils at an adaptation level corresponding with about 400 lux room illuminance.

Effect of Varying Levels of Glare on Contrast Sensitivity Measurements of Young Healthy Individuals Under Photopic and Mesopic Vision

Contrast sensitivity (CS), the ability to detect small spatial changes of luminance, is a fundamental aspect of vision. However, while visual acuity is commonly measured in eye clinics, CS is often not assessed. At issue is that tests of CS are not highly standardized in the field and that, in many cases, optotypes used are not sensitive enough to measure graduations of performance and visual abilities within the normal range. Here, in order to develop more sensitive measures of CS, we examined how CS is affected by different combinations of glare and ambient lighting in young healthy participants. We found that low levels of glare have a relatively small impact on vision under both photopic and mesopic conditions, while higher levels had significantly greater consequences on CS under mesopic conditions. Importantly, we found that the amount of glare induced by a standard built-in system (69 lux) was insufficient to induce CS reduction, but increasing to 125 lux with a custom system did cause a significant reduction and shift of CS in healthy individuals. This research provides important data that can help guide the use of CS measures that yield more sensitivity to characterize visual processing abilities in a variety of populations with ecological validity for non-ideal viewing conditions such as night time driving.

Light scattering in the human eye modelled as random phase perturbations

Light scattering in the eye affects the quality of vision and its effect increases with aging and related pathologies, such as cataracts. Simulating methods were developed in order to reproduce the effects of this phenomenon. We introduce a statistical model of wavefront perturbations at the pupil plane of the eye that replicates the characteristic angular distribution of the light distribution over the retina. Our approach is based on the parameterization of the discrete cosine spectrum of the wavefront perturbation. The model performance was experimentally validated with a dedicated setup using a liquid crystal on silicon device as a spatial phase modulator. This instrument can be used for further visual experiments with controlled induction of light scattering.

Intraocular light scatter, reflections, fluorescence and absorption: what we see in the slit lamp

PURPOSE

Much knowledge has been collected over the past 20 years about light scattering in the eye- in particular in the eye lens- and its visual effect, called straylight. It is the purpose of this review to discuss how these insights can be applied to understanding the slit lamp image.

RESULTS

The slit lamp image mainly results from back scattering, whereas the effects on vision result mainly from forward scatter. Forward scatter originates from particles of about wavelength size distributed throughout the lens. Most of the slit lamp image originates from small particle scatter (Rayleigh scatter). For a population of middle aged lenses it will be shown that both these scatter components remove around 10% of the light from the direct beam. For slit lamp observation close to the reflection angles, zones of discontinuity (Wasserspalten) at anterior and posterior parts of the lens show up as rough surface reflections. All these light scatter effects increase with age, but the correlations with age, and also between the different components, are weak. For retro-illumination imaging it will be argued that the density or opacity seen in areas of cortical or posterior subcapsular cataract show up because of light scattering, not because of light loss. NOTES: (1) Light scatter must not be confused with aberrations. Light penetrating the eye is divided into two parts: a relatively small part is scattered, and removed from the direct beam. Most of the light is not scattered, but continues as the direct beam. This non-scattered part is the basis for functional imaging, but its quality is under the control of aberrations. Aberrations deflect light mainly over small angles (<1°), whereas light scatter is important because of the straylight effects over large angles (>1°), causing problems like glare and hazy vision. (2) The slit lamp image in older lenses and nuclear cataract is strongly influenced by absorption. However, this effect is greatly exaggerated by the light path lengths concerned. This obviates proper judgement of the functional importance of absorption, and hinders the appreciation of the Rayleigh nature of what is seen in the slit lamp image.

Straylight as an Indicator for Cataract Extraction in Patients with Retinal Dystrophy

PURPOSE

Straylight reduces retinal sensitivity, which is particularly relevant in conditions with retinal dysfunction, such as retinitis pigmentosa (RP). Retinitis pigmentosa is associated with posterior subcapsular cataract (PSC), a cataract type that is known to cause severe disability glare (i.e., straylight). Study purposes were (1) to determine the severity of disability glare before and after cataract extraction (CE) in subjects with retinal dystrophy; (2) to study possible aggravation of disability glare due to the combination of retinal degradation and increased straylight from PSC; and (3) to evaluate whether straylight can be used to support the possible benefit of (early) CE.

DESIGN

Prospective, comparative study.

PARTICIPANTS

Sixteen patients (25 eyes) with retinal dystrophy scheduled for CE participated.

METHODS

Cataract severity was graded according to the Lens Opacities Classification System (LOCS) III. Preoperatively and postoperatively, corrected distance visual acuity (CDVA), spatial contrast sensitivity with the Pelli-Robson chart, and straylight were tested. Retinal function was assessed with Goldmann visual field and temporal contrast sensitivity (TCS). Temporal contrast sensitivity is a flicker test to evaluate central retinal sensitivity isolated from the eye's optical quality. Central retinal structure was assessed with spectral-domain OCT and fundus autofluorescence.

MAIN OUTCOME MEASURES

Preoperative and postoperative straylight were measured using the C-Quant (Oculus Optikgeräte GmbH, Wetzlar, Germany) and expressed as the logarithm of the straylight parameter s: log(s).

RESULTS

The average straylight value was 1.75 preoperatively and 1.45 postoperatively, 7.1 and 3.5 times higher than in a healthy young eye, respectively. Functionally significant improvement, defined as >0.20 log, was found in 72% of eyes for straylight and in 20% of eyes for CDVA. The CDVA and TCS were significantly correlated. Only straylight improvement was related to preoperative values; therefore, straylight was the only parameter that could be used to support postoperative improvement. In retinal dystrophy, eyes with cataract and a preoperative straylight value ≥1.66 log(s), a 50% chance of functionally significant log(s) improvement can be expected.

CONCLUSIONS

In patients with retinal dystrophy, straylight caused by cataract substantially aggravates visual disability, whereas CDVA is less affected. Therefore, straylight is a valuable (additional) indicator for beneficial CE in patients with retinal dystrophy and cataract.

Visual Discrimination Increase by Yellow Filters in Retinitis Pigmentosa

PURPOSE

The objective of this study was to evaluate, by halometry and under low illumination conditions, the effects of short-wavelength light absorbance filters on visual discrimination capacity in retinitis pigmentosa patients.

METHODS

This was an observational, prospective, analytic, and transversal study on 109 eyes of 57 retinitis pigmentosa patients with visual acuity better than 1.25 logMAR. Visual disturbance index (VDI) was determined using the software Halo 1.0, with and without the interposition of filters which absorb (totally or partially) short-wavelength light between 380 and 500 nm.

RESULTS

A statistically significant reduction in the VDI values determined using filters which absorb short-wavelength light was observed (p < 0.0001). The established VDIs in patients with VA logMAR <0.4 were 0.30 ± 0.05 (95% CI, 0.26-0.36) for the lens alone, 0.20 ± 0.04 (95% CI, 0.16-0.24) with the filter that completely absorbs wavelengths shorter than 450 nm, and 0.24 ± 0.04 (95% CI, 0.20-0.28) with the filter that partially absorbs wavelengths shorter than 450 nm, which implies a 20 to 33% visual discrimination capacity increase. In addition, a decrease of VDI in at least one eye was observed in more than 90% of patients when using a filter.

CONCLUSIONS

Short-wavelength light absorbance filters increase visual discrimination capacity under low illumination conditions in retinitis pigmentosa patients. Use of such filters constitutes a suitable method to improve visual quality related to intraocular light visual disturbances under low illumination conditions in this group of patients.

Ocular Straylight with Different Multifocal Contact Lenses

PURPOSE

Multifocal contact lenses have been growing in popularity as a modality to correct presbyopic eyes, although visual side effects such as disability glare have been reported. The objective of this study was to investigate the effect of multifocal contact lenses on disability glare by means of ocular straylight.

METHODS

A prospective randomized, comparative study was performed that included 16 subjects free of ocular pathology. Straylight was measured using a commercial straylight meter with the natural and dilated pupil. Participants were fitted with Proclear Multifocal (Distance/Near), ACUVUE Oasys for Presbyopia, and Air Optix Aqua Multifocal randomized to the left or right eye. Straylight measurements were repeated with the contact lens in situ after the pupil dilation. Results obtained with the dilated pupil without contact lens acted as a control.

RESULTS

Diameter of the natural and dilated pupil was 2.87 ± 0.40 mm and 7.45 ± 0.86 mm, respectively (P < .001). After pupil dilation, straylight increased from 0.92 ± 0.13 log(s) to 1.04 ± 0.11 log(s) (P < .001). Of the four studied lenses, a significant difference was only found between Air Optix and the control group (P = .006). The latter showed also slightly increased light scatter.

CONCLUSIONS

A difference in measured straylight was found between the studied multifocal lenses. The observed variability and the straylight-pupil size dependency should be taken into account to avoid elevated straylight in multifocal contact lens wearers. The reason for the observed differences in straylight must be the subject of future studies.

Changes in Intraocular Straylight and Visual Acuity with Age in Cataracts of Different Morphologies

Purpose

To investigate the significance of difference in straylight of cataract eyes with different morphologies, as a function of age and visual acuity.

Methods

A literature review to collect relevant papers on straylight, age, and visual acuity of three common cataract morphologies leads to including five eligible papers for the analysis. The effect of morphology was incorporated to categorize straylight dependency on the two variables. We also determined the amount of progression in a cataract group using a control group.

Results

The mean straylight was 1.22 log units ± 0.20 (SD) in nuclear (592 eyes), 1.26 log units ± 0.23 in cortical (776 eyes), and 1.48 log units ± 0.34 in posterior subcapsular (75 eyes) groups. The slope of straylight-age relationship was 0.009 (R² = 0.20) in nuclear, 0.012 (R² = 0.22) in cortical, and 0.014 (R² = 0.11) in posterior subcapsular groups. The slope of straylight-visual acuity relationship was 0.62 (R² = 0.25) in nuclear, 0.33 (R² = 0.13) in cortical, and 1.03 (R² = 0.34) in posterior subcapsular groups.

Conclusion

Considering morphology of cataract provides a better insight in assessing visual functions of cataract eyes, in posterior subcapsular cataract, particularly, in spite of notable elevated straylight, visual acuity might not manifest severe loss.

Effect of Cataract Opacity Type and Glaucoma Severity on Visual Field Index

PURPOSE

To determine the effect of cataract opacity type and glaucoma severity on the visual field index (VFI).

METHODS

A total of 152 eyes of 152 patients were analyzed. Patients with glaucoma, previous evaluation with the Swedish Interactive Threshold Algorithm-standard 24-2 VFs, visually significant cataracts, and VFs before surgery were included in this study. Cataract opacity was classified as cortical, nuclear sclerotic, or posterior subcapsular. The patients underwent phacoemulsification cataract extraction surgery. A postoperative VF test was done within 10 months of the previous VF. Glaucoma severity was classified by the postoperative mean deviation (MD) value. Changes in MD, pattern standard deviation (PSD), and VFI value before and after surgery were compared according to cataract opacity and glaucoma severity.

RESULTS

The mean age at cataract surgery was 72 ± 10 years. The MD, PSD, and VFI values were less influenced by nuclear sclerotic cataract opacity. In patients with early glaucoma (MD > -6), particularly with cortical cataract opacity, MD, PSD, and VFI improved after cataract extraction (p < 0.05). Cataract opacity could make interpreting the VF indices more difficult in patients with early glaucoma. VFI was a reliable index that was less affected by cataract extraction, except in patients with early glaucoma (MD > -6) and cortical cataract opacity.

CONCLUSIONS

Existing cataract opacity and the type of cataract opacity may affect the VF test results. Therefore, both glaucoma severity and the type of cataract opacity should be considered when interpreting VF results.

The (lack of) relation between straylight and visual acuity. Two domains of the point-spread-function

PURPOSE

The effect of cataract and other media opacities on functional vision is typically assessed clinically using visual acuity. In both clinical and basic research, straylight (the functional result of light scattering in the eye) is commonly measured. The purpose of the present study was to determine the link between these two measures: is visual acuity in cataract and other media opacities related to straylight?

METHODS

Interdependence between acuity and straylight is addressed from three different points of view: (1) Methodological: can acuity differences affect the measurement value of straylight, and vice versa? (2) Basic optics: does the optical process of light scattering in the human eye affect both straylight and visual acuity? (3) Statistical: how strongly are acuity and straylight correlated in the practice of important clinical conditions? Experimental and theoretical aspects will be considered, with a focus on normal ageing and cataract formation.

RESULTS

(1) Methodological: testing potential effects of acuity, artificially manipulated with positive trial lenses, showed no effect on measured straylight values. Since light scattering in the eye involves a low percentage of the light and has large angular spreading, contrast reduction due to straylight is limited, resulting in virtually absent acuity effects. (2) Basic optics: light scattering from the human donor eye lens is found to have virtually no effect in the centre of the point-spread-function, also for cataractous lenses, resulting in virtually absent acuity effects. (3) Statistical: literature data on straylight and visual acuity show a weak correlation for the important groups of normal ageing and cataract populations.

CONCLUSIONS

The point-spread-function of the normal ageing and cataractous human eye is built upon two rather independent basic parts. Aberrations control the central peak. Light scattering controls the periphery from about 1° onwards. The way acuity and straylight are measured ensures no confounding between them. Statistically within the normal ageing and cataract populations, visual acuity and straylight vary quite independently from each other. Visual acuity losses with cataract and other media opacities are not due to straylight, but caused by aberrations and micro-aberrations. Straylight defines disability glare, and causes symptoms of glare, haloes, hazy vision etc. Overall, visual acuity and straylight are rather independent aspects of quality of vision.

Validation of a spectral light scattering method to differentiate large from small particles in intraocular lenses

A psychophysical approach has been designed to measure straylight from intraocular lenses (IOLs) in vitro. This approach uses a clinical straylight meter (C-Quant) and an observer's eye as optical detector. Based on this, we introduced a method for study of straylight-wavelength dependency for IOLs. This dependency can be used to distinguish between 2 types of scattering particles (small and large) as defined by Mie theory. Validation was performed using a turbidity standard and scattering filters. Several IOLs were analyzed to identify potential scattering sources. Large particles were found to predominate in scattering from the studied lenses. This was confirmed by straylight-angular dependency found in these IOLs.

Performance of a differential contrast sensitivity method to measure intraocular scattering

Increased intraocular scatter degrades quality of vision, especially in the presence of glare sources. Standard tests, such as visual acuity, are not well suited to capture this condition. There are specific methods to measure intraocular scatter, but require dedicated instruments. In this work, we propose a method to estimate the amount of scatter by combining to sequential measurements of the contrast sensitivity function for two conditions, with and without a glare source. We applied the approach in a group of young subjects with no know ocular pathology fitted with photographic diffusing filters. The straylight estimates were compared with those provided by two alternative techniques, one based on the compensation comparison method and the other the optical integration. The results obtained with the three approaches were in a good agreement, demonstrating the feasibility of the proposed method.

Influence of macular pigment optical density spatial distribution on intraocular scatter

PURPOSE

This study evaluated the summed measures of macular pigment optical density (MPOD) spatial distribution and their effects on intraocular scatter using a commercially available device (C-Quant, Oculus, USA).

METHODS

A customized heterochromatic flicker photometer (cHFP) device was used to measure MPOD spatial distribution across the central 16° using a 1° stimulus. MPOD was calculated as a discrete measure and summed measures across the central 1°, 3.3°, 10° and 16° diameters. Intraocular scatter was determined as a mean of 5 trials in which reliability and repeatability measures were met using the C-Quant. MPOD spatial distribution maps were constructed and the effects of both discrete and summed values on intraocular scatter were examined.

RESULTS

Spatial mapping identified mean values for discrete MPOD [0.32 (s.d.=0.08)], MPOD summed across central 1° [0.37 (s.d.=0.11)], MPOD summed across central 3.3° [0.85 (s.d.=0.20)], MPOD summed across central 10° [1.60 (s.d.=0.35)] and MPOD summed across central 16° [1.78 (s.d.=0.39)]. Mean intraocular scatter was 0.83 (s.d.=0.16) log units. While there were consistent trends for an inverse relationship between MPOD and scatter, these relationships were not statistically significant. Correlations between the highest and lowest quartiles of MPOD within the central 1° were near significance.

CONCLUSIONS

While there was an overall trend of decreased intraocular forward scatter with increased MPOD consistent with selective short wavelength visible light attenuation, neither discrete nor summed values of MPOD significantly influence intraocular scatter as measured by the C-Quant device.

Forward light scatter and visual acuity before and after intrastromal corneal ring segment implantation at different stages of keratoconus

PURPOSE

To assess forward light scatter (stray light) before and after intrastromal corneal ring segment (ICRS) implantation at different stages of keratoconus and to examine correlation between postoperative stray light and visual acuity (VA).

METHODS

In 27 eyes of 27 subjects with keratoconus, stray light was determined using the compensation comparison technique before and 6 months after ICRS implantation. Monocular corrected distance VA (CDVA) was measured using a high-contrast logMAR letter chart. Corneal higher-order aberrations (HOAs), contrast sensitivity (CS) and minimum corneal thickness (CT) were also measured.

RESULTS

Mean CDVA was 0.42 ± 0.28 preoperatively and 0.24 ± 0.15 logMAR postoperatively (p < 0.01). Mean corneal coma-like aberration decreased postoperatively (RMS 0.55 ± 1.18 μm, p < 0.01). Minimum CT increased 25.31 ± 18.59 μm (p < 0.01). Mean preoperative and postoperative stray light were 1.36 ± 0.31 and 1.48 ± 0.32 log units, respectively (p < 0.01). Mean changes produced in stray light (worsening) were 0.03 ± 0.21 (p > 0.05) for stage I, 0.13 ± 0.14 (p = 0.013) for stage II and 0.18 ± 0.21 (p = 0.023) for stage III. Significant positive correlation (r = 0.47, p = 0.01) was detected between postoperative stray light and postoperative CDVA such that as stray light increased, CDVA worsened (higher logMAR values). Postoperative stray light was neither associated with HOAs, CS nor minimum CT.

CONCLUSIONS

Stray light values in these patients with keratoconus were higher than normal preoperatively. In eyes with stage II and III keratoconus, stray light increased 6 months after ICRS placement. Higher postoperative stray light was correlated with a worse visual acuity outcome.

Capacity of straylight and disk halo size to diagnose cataract

PURPOSE

To examine the capacity of straylight and disk halo size to diagnose cataract.

SETTING

Faculty of Optics and Optometry, Universidad Complutense de Madrid, Spain.

DESIGN

Prospective study.

METHODS

Straylight, disk halo radius, and high-contrast corrected distance visual acuity (CDVA) measurements were compared between patients with age-related cataract and age-matched normal-sighted control subjects by calculating the area under the curve (AUC) receiver operating characteristic.

RESULTS

Measurements were made in 53 eyes of 53 patients with a mean age of 67.94 years ± 7.11 (SD) and 31 eyes of 31 controls with a mean age 66.06 ± 5.43 years. Significantly worse (P < .001) mean straylight (1.38 ± 0.24 log[s]), mean disk halo radius (2.40 ± 0.18 log minutes of arc [arcmin]), and mean CDVA (0.17 ± 0.11 logMAR) were recorded in the cataract group than in the control group (1.17 ± 0.11 log[s], 2.10 ± 0.16 log arcmin, and 0.08 ± 0.08 logMAR). Significant differences in AUCs were observed for disk halo radius (0.89 ± 0.04) versus straylight (0.77 ± 0.05) (P = .03) and disk halo radius versus CDVA (0.72 ± 0.05) (P = .001). The comparison of disk halo radius versus the discriminant function with input from CDVA and straylight (0.80 ± 0.05) was at the limit of significance only (0.091 ± 0.05, P = .051).

CONCLUSION

Although all 3 variables discriminated well between normal eyes and eyes with cataract, the disk halo radius showed the best diagnostic capacity.

FINANCIAL DISCLOSURE

Neither author has a financial or proprietary interest in any material or method mentioned.