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

Effect of the chromaticity of stimuli on night vision disturbances

The perception of halos and other night vision disturbances is a common complaint in clinical practice. Such visual disturbances must be assessed in order to fully characterize each patient's visual performance, which is particularly relevant when carrying out a range of daily tasks. Visual problems are usually assessed using achromatic stimuli, yet the stimuli encountered in daily life have very different chromaticities. Hence, it is important to assess the effect of the chromaticity of visual stimuli on night vision disturbances. The aim of this work is to study the influence of the chromaticity of different visual stimuli on night vision disturbances by analyzing straylight and visual discrimination under low-light conditions. For that, we assessed the monocular and binocular visual discrimination of 27 subjects under low illumination using the Halo test. The subjects' visual discrimination was assessed after exposure to different visual stimuli: achromatic, red, green, and blue, both at the monitor's maximum luminance and maintaining the same luminance value for the different visual stimuli. Monocular straylight was also measured for an achromatic, red, green, and blue stimuli. The blue stimulus had the greatest effect on halos in both monocular and binocular conditions. Visual discrimination was similar for the red, green, and achromatic stimuli, but worsened at lower luminance. The greatest influence of straylight was observed for the blue stimulus. In addition, visual discrimination correlated with straylight measurements for achromatic stimuli, wherein greater straylight values correlated with an increased perception of halos and other visual disturbances.

Higher order aberrations in keratoconus‏

INTRODUCTION

Keratoconus is a progressive disorder of the cornea that causes thinning (Sedaghat et al. in Sci Rep 11(1):11971, 2021), ectasia, and irregular astigmatism, resulting in poor visual acuity that cannot be corrected with standard sphero-cylindrical spectacle lenses. One feature distinguishing keratoconic corneas is ocular aberrations, manifesting up to five or six times the amount of higher-order aberrations than a normal, healthy eye. These aberrations can cause visual disturbances even at the very early stages of the disease.

METHODS

In the past, a diagnosis was derived from clinical symptoms, but technological advances have revealed multiple pre-clinical features, allowing for the differentiation between keratoconic and normal eyes at a much earlier stage. These include anterior and posterior corneal surface elevations, the corneal pachymetry profile, corneal epithelial patterns, wavefront aberration metrics, and corneal biomechanics (Sedaghat et al. in Sci Rep 11(1):11971, 2021).This review discusses the aberrations associated with keratoconus, how to measure them, and treatment methods to minimize their negative influence.

CONCLUSIONS

Early diagnosis can lead to early treatment and may allow for arresting progression, thereby improving the long-term prognosis. With the acceleration of refractive surgery, it is important to identify patients with keratoconus, as they are usually contraindicated for refractive surgery.

Intraocular Straylight and Multifocal Soft Contact Lens Fit With a Myopia Control Approach

OBJECTIVES

Center-distance multifocal contact lenses (MFCLs) are used to slow myopia progression. We examined the effect of two MFCLs on intraocular straylight values in myopic individuals.

METHODS

Twenty-five young myopic adults were enrolled and were fit with three contact lenses (Biofinity sphere, Biofinity Multifocal, and NaturalVue Multifocal) in a random order over two study visits. Pupil size (NeurOptics VIP-300, Laguna Hills, CA) and contact lens centration were measured. Right eye intraocular straylight measurements were collected (OCULUS C-Quant; Wetzlar, Germany) and compared with a spectacle trial lens. Log straylight (LogSL) values and straylight residuals were analyzed using repeated-measures analyses of variance with Tukey-corrected post hoc t -tests.

RESULTS

The mean participant age (±SD) was 24.1±1.5 years, and right eye spherical equivalent refractive error was -3.38±1.53 DS. There was no difference in mesopic pupil size between visits ( P =0.68) and no difference in contact lens centration between lenses ( P =0.99). LogSL values differed by lens type ( P =0.004). LogSL with the spectacle trial lens was significantly greater than with each contact lens type (all P <0.05), but there were no significant differences in LogSL between the three contact lenses (all P >0.05). There was no difference between the three contact lens designs for straylight residuals ( P =0.33).

CONCLUSIONS

Measured intraocular straylight for both MFCLs was not different than with a spherical soft contact lens. A significant increase in intraocular straylight with spectacle trial lens correction was observed compared with all contact lenses.

Changes in straylight after cataract surgery

PURPOSE

To investigate straylight in the immediate postoperative period after cataract surgery.

SETTING

Amphia Hospital, Breda, the Netherlands.

DESIGN

Prospective, comparative, single-arm, single-center, single-surgeon study.

METHODS

Patients underwent cataract surgery on both eyes. 1 eye was randomly selected for implantation with a Clareon CNA0T0 intraocular lens (IOL); the fellow eye received a Vivinex XY1 IOL. Straylight was measured with the C-Quant straylight meter.

RESULTS

25 patients were included. Preoperatively, 1 day, 1 week, 1 month, and 3 months postoperatively, eyes with a CNA0T0 IOL had straylight levels (mean ± SD) of 1.48 ± 0.23, 1.26 ± 0.20, 1.06 ± 0.19, 1.11 ± 0.25, and 1.09 ± 0.20 log(s), respectively. For eyes with an XY1 IOL, these values were 1.48 ± 0.21, 1.41 ± 0.41, 1.10 ± 0.20, 1.13 ± 0.20, and 1.16 ± 0.20 log(s), respectively. From 1 week postoperatively, straylight values did not change (1 week vs 3 months: P = .40 and P = .14 and 1 month vs 3 months: P = .74 and P = .50 for CNA0T0 and XY1, respectively). The Pearson correlation coefficient for straylight values between the 2 eyes of individual subjects was 0.80 at 3 months.

CONCLUSIONS

Straylight levels can be considered stable 1 week after cataract surgery. We believe it is safe to use straylight measurements 1 month postoperatively for clinical trials. Straylight is highly correlated between the 2 eyes of an individual postoperatively.

Imaging Function and Relative Light Transmission of Explanted Opacified Hydrophilic Acrylic Intraocular Lenses

We evaluated the influence of intraocular lens (IOL) opacification on the optical performance of explanted hydrophilic acrylic IOLs. We performed a laboratory analysis of 32 Lentis LS-502-1 (Oculentis GmbH, Berlin, Germany) IOLs, explanted due to opacification, in comparison with six clear unused samples of the same IOL model. Using an optical bench setup, we obtained modulation transfer function (MTF), Strehl ratio, two-dimensional MTF, and United States Air Force (USAF) chart images. In addition, we assessed light transmission through the IOLs. The MTF values of opacified IOLs at 3-mm aperture were similar to those of clear lenses, with the median (interquartile range) values of 0.74 (0.01) vs. 0.76 (0.03) at the spatial frequency of 50 line pairs per millimeter in clear and opacified IOLs, respectively. The Strehl ratio of opacified lenses was not lower than that of clear lenses. The USAF-chart analysis showed a considerable reduction in brightness in opacified IOLs. The median (interquartile range) relative light transmission of opacified IOLs in comparison to clear lenses was 55.6% (20.8%) at the aperture size of 3 mm. In conclusion, the explanted opacified IOLs had comparable MTF values to those of clear lenses but significantly reduced light transmission.

Diurnal Variation in Straylight in Patients With Fuchs Endothelial Corneal Dystrophy and Controls

PURPOSE

The goal of this study was to investigate diurnal changes in intraocular straylight in relation to other corneal parameters and subjective complaints in patients with Fuchs endothelial dystrophy and healthy controls.

METHODS

This is a prospective study conducted in 2 tertiary care hospitals in Germany and the Netherlands. Patients with Fuchs endothelial dystrophy (n = 71) and healthy controls (n = 34) were included. Patients with Fuchs dystrophy were grouped by the presence of subjective complaints and measured over multiple time points during the day. Measurements included intraocular straylight using the C-Quant and corneal thickness and backscatter using a Scheimpflug camera. A separate group of healthy controls was measured intensively with repeated straylight measurements directly after waking. An exponential decay model was used to model the diurnal change.

RESULTS

Healthy controls showed an average straylight baseline of 1.17 log(s) with an increase in straylight after waking of 0.22 log(s). In the repeated measurements subgroup, the increase in morning straylight lasted for 22 minutes. Patients with Fuchs dystrophy showed a morning increase in straylight of 0.21 log(s) present up to 4 hours after waking before reaching an average baseline of 1.30 log(s). Straylight was positively correlated with anterior corneal backscatter, r = 0.21, P = 0.022, and corneal thickness, r = 0.46, P < 0.01.

CONCLUSIONS

Healthy eyes experience a diurnal straylight increase similar to patients with Fuchs dystrophy in intensity. However, in Fuchs dystrophy, the resolution of increased straylight is prolonged over multiple hours compared with minutes in healthy eyes. This suggests pathological exacerbation of a physiological diurnal change. This mechanism can play a role in subjective complaints experienced by patients with Fuchs dystrophy.

Comparison of the effects of alcohol and cannabis on visual function and driving performance. Does the visual impairment affect driving?

BACKGROUND

Alcohol and cannabis are the most widely consumed psychoactive substances worldwide. This study compared the effects of alcohol and cannabis on visual function and driving performance, as well as self-perceived effects. Also, the relationship between visual effects under the influence and driving performance was studied.

METHODS

Sixty-four young drivers, with a history of alcohol and/or cannabis use were included. Of these, 33 were allocated to the alcohol group and 31 to the cannabis group. All participants were evaluated in a baseline session. The alcohol group underwent two sessions: after drinking 300 ml and 450 ml of red wine (A1 and A2). The cannabis group attended one session after smoking cannabis (C). Visual function was evaluated at the contrast sensitivity, stereoacuity, and intraocular straylight level. Participants drove a driving simulator. A general score (overall visual score, OVS; overall driving performance score, ODPS) was obtained for both visual functioning and driving performance.

RESULTS

The evaluation of visual function demonstrated a significant impairment in OVS for all conditions studied (A1, p = 0.005; A2, p < 0.001; C, p < 0.001) with respect to the baseline session. General driving performance (ODPS) demonstrated a significant worsening for the A2 condition (p = 0.003). Finally, a significant relationship between driving performance and visual function was found (rho=0.163, p = 0.039 and χ² = 4.801, p = 0.028).

CONCLUSIONS

Cannabis and alcohol use negatively impact visual function. However, driving performance was only significantly affected by the higher alcohol dose. This impairment in visual function was significantly associated with worse driving performance.

The Effect of Induced Intraocular Stray Light on Recognition Thresholds for Pseudo-High-Pass Filtered Letters

Purpose

The Moorfields Acuity Chart (MAC)—comprising pseudo-high-pass filtered “vanishing optotype” (VO) letters—is more sensitive to functional visual loss in age-related macular degeneration (AMD) compared to conventional letter charts. It is currently unknown the degree to which MAC acuity is affected by optical factors such as cataract. This is important to know when determining whether an individual's vision loss owes more to neural or optical factors. Here we estimate recognition acuity for VOs and conventional letters with simulated lens aging, achieved using different levels of induced intraocular light scatter.

Methods

Recognition thresholds were determined for two experienced and one naive participant with conventional and VO letters. Stimuli were presented either foveally or at 10 degrees in the horizontal temporal retina, under varying degrees of intraocular light scatter induced by white resin opacity-containing filters (WOFs grades 1 to 5).

Results

Foveal acuity only became significantly different from baseline (no filter) for WOF grade 5 with conventional letters and WOF grades 4 and 5 with VOs. In the periphery, no statistical difference was found for any stray-light level for both conventional and VOs.

Conclusions

Recognition acuity measured with conventional and VOs is robust to the effects of simulated lens opacification, and thus its higher sensitivity to neural damage should not simultaneously be confounded by such optical factors.

Translational Relevance

The MAC may be better able to differentiate between neural and optical deficits of visual performance, making it more suitable for the assessment of patients with AMD, who may display both types of functional visual loss.

Speed management across road environments of varying complexities and self-regulation behaviors in drivers with cataract

Evidence suggests that drivers with cataract self-regulate their driving, but there is a lack of objective information. This study compared speed behavior in older drivers with and without cataract and how the parameter is influenced by road traffic complexity and driver characteristics. The study included 15 drivers with cataract and a control group of 20 drivers. Visual status was assessed using visual acuity, contrast sensitivity, and intraocular straylight. Speed management was studied using a driving simulator. Driving difficulty and self-regulation patterns were evaluated by means of the Driver Habits Questionnaire (DHQ). The cataract group showed a significant decrease in visual function in all the parameters evaluated (p < 0.05). These drivers tended to drive at lower speeds than the control group. Road characteristics, gender, and intraocular straylight in the better eye were identified as significant predictors of speed management. Drivers with cataract experience greater driving difficulty, particularly when driving at night (p < 0.05). Drivers with cataract reduce their driving speed more than older drivers without visual impairment. The straylight parameter may be a good indicator of each driver's subjective perception of their own visual ability to drive. This work helps shed light on the mechanisms through which age-related visual impairment influences driving behavior.

The effect of mental load on psychophysical and visual evoked potential visual acuity

PURPOSE

Under real-world conditions, tasks dependent on visual acuity may need to be performed in the presence of a mental load arising from concurrent, non-visual tasks. Therefore, measuring visual acuity concurrently with mentally demanding tasks may reflect a patient's vision more accurately. This study was designed to evaluate the impact of task-induced mental load on high contrast visual acuity, as measured using a letter chart and estimated via sweep visual evoked potentials (sweep VEP).

METHODS

Visual acuity was determined using the Freiburg Vision Test, and also using sweep VEP tested stepwise, from coarse to fine, over 13 spatial frequencies, in 31 healthy participants (aged 22.4 ± 3.6 years). Recordings were repeated while participants concurrently performed an auditory 2-back task. Mental load of the n-back task was confirmed through subjective ratings.

RESULTS

Visual acuity determined with the Freiburg Vision Test worsened from -0.02 ± 0.12 to 0.04 ± 0.15 logMAR under mental load (p = 0.03). Visual acuities estimated by sweep VEPs worsened from 0.38 ± 0.1 to 0.47 ± 0.1 logMAR (p < 0.001). While the slope of the VEP amplitude versus spatial frequency function steepened significantly with mental load (p = 0.01), VEP noise levels were not significantly affected (p = 0.07).

CONCLUSION

Visual acuity reduces significantly with a concurrent task that produces mental load. At least part of this reduction appears to be related to alterations in responses within the visual cortex, rather than being purely attributable to higher-level distraction effects.

Surface light scattering from 1-piece hydrophobic acrylic intraocular lenses with hydroxyethyl methacrylate: contralateral observation for 7 years

PURPOSE

To quantitatively and intraindividually compare surface light scattering for 7 years after implantation of Clareon and AcrySof intraocular lenses (IOLs).

SETTING

Miyata Eye Hospital, Miyazaki, Japan.

DESIGN

Retrospective comparative case series.

METHODS

Clinical records of eyes that had contralateral implantation of SN60WF and SY60WF IOLs were reviewed. Light scattering on the anterior surface of IOLs, corrected distance visual acuity (CDVA), and mesopic and photopic contrast sensitivities were examined at 1 year, 3 years, and 7 years postoperatively, and they were intraindividually compared.

RESULTS

34, 19, and 16 patients visited at 1 year, 3 years, and 7 years postoperatively, respectively. Surface light scattering in eyes with SY60WF IOL was significantly reduced, and the rate of increase was 2.74 computer compatible tapes per year. Although there were prominent increases in eyes with SN60WF IOL, no statistically significant difference was found in their CDVA and contrast sensitivities.

CONCLUSIONS

In eyes with Clareon IOLs, the development of surface light scattering was suppressed up to 7 years. The increase rate demonstrated that the visual acuity would be least deteriorated up to 12 years postoperatively, whereas the influence of straylight induced should be investigated.

Visual performance after the deterioration of retinal image quality: induced forward scattering using Bangerter foils and fog filters

We induced and evaluated different levels of retinal-image degradation using Bangerter foils and fog filters. We found increased straylight and an important deterioration in visual performance, assessed by means of visual acuity, contrast threshold, and visual discrimination capacity. Bangerter foils induced forward scattering levels comparable to those observed in mature to severe cataracts, with an important impact of halos and starbursts. Fog filters induced lower levels of intraocular scattering, although luminous veils and circular halos were reported. The visual disturbance index positively correlated with intraocular scattering and straylight. Our results show retinal-image quality has an important influence on night-vision performance.

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.

Factors Influencing Contrast Sensitivity Function in Eyes with Mild Cataract

This study was aimed to evaluate the relationship between the area under the log contrast sensitivity function (AULCSF) and several optical factors in eyes suffering mild cataract. We enrolled 71 eyes of 71 patients (mean age, 71.4 ± 10.7 (standard deviation) years) with cataract formation who were under surgical consultation. We determined the area under the log contrast sensitivity function (AULCSF) using a contrast sensitivity unit (VCTS-6500, Vistech). We utilized single and multiple regression analyses to investigate the relevant factors in such eyes. The mean AULSCF was 1.06 ± 0.16 (0.62 to 1.38). Explanatory variables relevant to the AULCSF were, in order of influence, logMAR best spectacle-corrected visual acuity (BSCVA) (p < 0.001, partial regression coefficient B = −0.372), and log(s) (p = 0.023, B = −0.032) (adjusted R² = 0.402). We found no significant association with other variables such as age, gender, uncorrected visual acuity, nuclear sclerosis grade, or ocular HOAs. Eyes with better BSCVA and lower log(s) are more susceptible to show higher AULCSF, even in mild cataract subjects. It is indicated that both visual acuity and intraocular forward scattering play a role in the CS function in such eyes.

Effects of cannabis on visual function and self-perceived visual quality

Cannabis is one of the most used drugs of abuse in the world. The objective of this study was to analyze the effects of smoking cannabis on vision and to relate these to those perceived by the user. Thirty-one cannabis users participated in this study. Visual function assessment was carried out in a baseline session as well as after smoking cannabis. We evaluated static visual acuity, contrast sensitivity, stereoacuity, accommodative response, straylight, night-vision disturbances (halos) and pupil size. The participants were also divided into two groups depending on whether they perceived their vision to have worsened after smoking cannabis. A logistic regression analysis was employed to identify which visual test could best predict self-perceived visual effects. The study found that smoking cannabis has significant adverse effects on all the visual parameters analyzed (p < 0.05). Self-perceived visual quality results revealed that about two thirds of the sample think that smoking cannabis impairs their vision. Contrast sensitivity, specifically for the spatial frequency 18 cpd, was identified as the only visual parameter significantly associated with self-perceived visual quality (Odds Ratio: 1.135; p = 0.040). Smoking cannabis is associated with negative effects on visual function. Self-perceived visual quality after smoking cannabis could be related to impaired contrast sensitivity.

A narrative review of intraocular lens opacifications: update 2020

The opacifications of intraocular lenses (IOLs) can significantly impact patients visual quality. Despite the identification of specific risk factors, manufacturing changes, opacifications are not eliminated. Likewise, more attention in recent studies was paid to possible new risk factors, however one of the most important purposes of the studies remains opacifications effect on visual performance, which could be disturbed in different aspects. The aim of this review is to discuss the main risk factors of IOLs opacification in particular IOL types, and its impact on vision quality. Different risk factors were discussed in the study, including the material of IOLs, the impact of the breakdown of blood-aqueous barrier (BAB), and certain surgeries that can be associated with opacification formation. Glistenings occur more often in a hydrophobic material, however, the changes in water content of the IOLs can significantly reduce the formation of glistenings. The studies showed a significant effect of intraocular injection of exogenous air or gas during Descemet-stripping endothelial keratoplasty, Descemet-stripping automated endothelial keratoplasty, Descemet membrane endothelial keratoplasty, and pars plana vitrectomy on calcification formation. It raises a concern, as the incidence of these surgeries is increasing. Visual acuity decreases significantly after the calcification in IOLs occurs, and it usually causes IOLs exchange. However, disability glare seems to be more affected in patients with IOLs, which were affected by glistenings than visual acuity. Disability glare is associated with increased levels of straylight, which was widely evaluated in recent studies and it was reported to be a susceptible measurement to detect the presence of IOLs pathology. For future researches, it should be noticed that disability glare and straylight are more appropriate in evaluating IOLs opacification effect on visual quality than visual acuity. While reviewing the main risk factors of IOLs opacifications particular attention must be paid on calcification occurrence in hydrophilic acrylic IOLs after surgeries with intraocular injection of exogenous air or gas.

Impact of Age-Related Vision Changes on Driving

Aging leads to impaired visual function, which can affect driving—a very visually demanding task—and has a direct impact on an individual’s quality of life if their license is withdrawn. This study examined the associations between age-related vision changes and simulated driving performance. To this end, we attempted to determine the most significant visual parameters in terms of evaluating elderly drivers’ eyesight. Twenty-one younger drivers (aged 25–40) were compared to 21 older drivers (aged 56–71). Study participants were assessed for visual acuity, contrast sensitivity, halos, and intraocular straylight, which causes veiling luminance on the retina and degrades vision. Driving performance was evaluated using a driving simulator. The relationships between simulated driving performance and the visual parameters tested were examined with correlation analyses and linear regression models. Older drivers presented impairment in most visual parameters (p < 0.05), with straylight being the most significantly affected (we also measured the associated effect size). Older drivers performed significantly worse (p < 0.05) in the simulator test, with a markedly lower performance in lane stability. The results of the multiple linear regression model evidenced that intraocular straylight is the best visual parameter for predicting simulated driving performance (R² = 0.513). Older drivers have shown significantly poorer results in several aspects of visual function, as well as difficulties in driving simulator performance. Our results suggest that the non-standardized straylight evaluation could be significant in driver assessments, especially at the onset of age-related vision changes.

The effects of light scatter when using a photochromic vs. non-photochromic contact lens

PURPOSE

To assess the visual effects of wearing both an activated and an inactivated photochromic contact lens, with a direct comparison to a non-photochromic contact lens worn in the fellow eye. This study focused on the visual effects of scatter quantified as the minimum distance between two points of light, and the diameter of the halo and starbursts that surround a bright white point source.

METHODS

60 subjects (aged 18-65 years) were measured in a contralateral design where lens type was randomly assigned, one type to each eye. During activated testing, all visual measures of both study lenses were made while each eye was illuminated by a violet (λ_max=365, half bandwidth 20nm) activator, which caused steady-state activation of the photochromic lens during the period of testing. Two-point thresholds were determined by measuring the minimum distance between two points of broadband xenon light. Glare geometry was measured using an aperture (∼4mm) that created a bright point source of light 45 inches from the plane of the eye. Between the point source and subject, a centering precision caliper was used to measure lateral spread of halos (diffusion around the source) and visual spokes. The head was stabilized using an adjustable head-rest assembly and the eye was aligned and monitored with a bore camera.

RESULTS

Compared to the non-photochromic lens, and based on the stimulus conditions used in these measurements, the activated and inactivated photochromic lens reduced the light spread using the two-point threshold technique by 32% and 19% respectively; the diameter of the halos were reduced by 44% and 16% respectively; and the spokes were narrowed by 39% and 20% respectively. Based on 95% confidence interval testing, these effects were all statistically significant (p<0.05).

CONCLUSIONS

These results are consistent with previous data showing that soft contact lenses with a photochromic additive can improve many aspects of visual function, consistent with their level or activation. Our past data focused on visual function under bright light conditions (e.g., glare disability, discomfort, photostress recovery and chromatic contrast) with an activated photochromic. In this study, we found differences even in the inactivated state, using less intense stimuli (10cd/m² at the source). This suggests that the photochromic lens improves the effects of light scatter even at lower luminance.

Straylight due to intraocular lens opacification in a patient with asteroid hyalosis

Purpose

To report a rare case of intraocular lens (IOL) calcification in the presence of asteroid hyalosis with in-vivo measurements of straylight before and after treatment.

Observations

A patient with asteroid hyalosis presented with complaints of disability glare due to calcifications on the posterior surface of the IOL. Straylight, measured with the C-Quant, was 8.2x elevated compared to normal (log(s) 2.08). Dissolution of the posterior face IOL deposits was performed with a neodymium-doped yttrium aluminum garnet (Nd:YAG) laser, resulting in a significant decrease in straylight (log(s) 1.76), congruent with the patient's subjective improvement.

Conclusions and importance

To the best of our knowledge, this is the first report describing a patient with an opacified IOL due to asteroid hyalosis with in-vivo measurements of straylight before and after treatment. It illustrates that awareness of glare complaints in patients with an opacified IOL is important, documentation with C-Quant measurements may be helpful in indicating treatment, evaluating the treatment, and following up the patient, and treatment with a Nd:YAG laser may dissolve the opacifications to a clinically satisfactory level.

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).

Experimental and analytical quantification of light scattering from vacuoles in intraocular lenses

PURPOSE

To develop an advanced test methodology for quantification of scattered light from intraocular lenses (IOLs) and to evaluate the correlation between IOL vacuole characteristics and measured scattered light.

SETTING

U.S. Food and Drug Administration, Optical Therapeutics and Medical Nanophotonics Laboratory, Silver Spring, Maryland, USA.

DESIGN

Experimental and analytical study.

METHODS

Twenty-four IOLs containing vacuoles were evaluated using a digital microscopy approach for identifying and characterizing the vacuoles present. A scanning light scattering profiler (SLSP) was used to evaluate and quantify the amount of scattered light from each IOL and from a 25th control IOL without any vacuoles. A variety of IOLs and vacuoles were also modeled in a Zemax simulation of the SLSP, and the simulated scattered light was modeled.

RESULTS

The scattered light as measured with SLSP was well correlated with vacuole characteristics, specifically density and size, as measured under the digital microscope for the 24 vacuole-containing IOLs. Additional correlations were found between vacuole sizes, orientations, and the angle at which light was scattered most severely. These correlations were also present in the Zemax model.

CONCLUSIONS

Vacuole optical characteristics can be well correlated with measured scatter, demonstrating an ability to predict scattered light based solely on microscope evaluation. Furthermore, the quantitative amount of scatter predicted with Zemax simulations trended closely with the experimentally measured trends.

The Effect of Capsulotomy Shape on Intraocular Light-Scattering after Nd:YAG Laser Capsulotomy

Purpose

To investigate the effects of capsulotomy shape on the visual acuity and visual quality after neodymium: yttrium aluminum garnet laser capsulotomy.

Methods

In this study, a total of 42 eyes from 35 patients with posterior capsule opacification were divided into the circular and cruciate groups. The corrected distance visual acuity (CDVA), objective scatter index (OSI), modulation transfer function cutoff (MTF cutoff), Strehl ratio, and Optical Quality Analysis System values at contrasts of 100%, 20%, and 9% (OV-100, OV-20, and OV-9) were measured at precapsulotomy and 1 week and 1 month postcapsulotomy. The pseudophakic dysphotopsia questionnaire (PDQ) was used to evaluate the subjects' satisfaction with treatment.

Results

OSI values were significantly higher in the cruciate group than in the circular group at 1 week and 1 month after capsulotomy (P=0.013 and P < 0.001). No significant difference was found in the OSI values between the two groups before capsulotomy (t = 0.52; P=0.61). The decrease in OSI was higher in the circular group than in the cruciate group at 1 week and 1 month after capsulotomy (P=0.036 and P=0.019). No significant differences were found in the Strehl ratio, MTF cutoff, CDVA, OV-100, OV-20, and OV-9 between the two groups at 1 week and 1 month after capsulotomy (P > 0.05). The PDQ results showed that patients with circular-shaped capsulotomy complained less with intolerance of bright lights than those with cruciate-shaped capsulotomy.

Conclusions

Circular-shaped capsulotomy can induce less intraocular light scattering and increase patient satisfaction.

Intraocular scattering as a predictor of driving performance in older adults with cataracts

Cataracts can limit a person’s ability to perform vision-dependent tasks safely, affecting the quality of life of older people. This study examines the relationship between visual function and driving, by studying which visual parameters might be important for predicting driving performance in older drivers with and without cataracts, ascertaining whether the objective measurement of intraocular scattering should be considered in assessment procedures for older drivers. This cross-sectional study involved a total of 20 older drivers (10 patients with bilateral cataracts and 10 control subjects). All participants were examined for visual acuity, contrast sensitivity, visual discrimination capacity, and intraocular scattering. Driving performance was also tested using a driving simulator. To study the relationship between visual parameters and driving performance, a correlation analysis and regression model were used. Drivers with cataracts showed a significantly impaired (p<0.05) visual function, with an Objective Scattering Index (OSI) 3.5 times greater than the control group. Driving performance was also significantly worse (p<0.05) in drivers with cataracts, reflected by a notable deterioration in lane keeping. The correlation analysis showed significant associations between driving performance and all the visual parameters studied. Finally, the regression model revealed that the OSI was the best predictor of driving performance, accounting for 51.3% of its variance. Visual function and driving performance are markedly deteriorated when cataracts are present. Our results demonstrate that the objective scattering index (OSI) has a high predictive power when it comes to simulated driving performance in older drivers, both with and without cataracts, suggesting that scatter measurements could be important in helping better understand visual limitations in older drivers.

Do Polymer Coatings Change the Aberrations of Conventional and Wavefront-guided Scleral Lenses?

SIGNIFICANCE

The findings of this study indicate that patients could simultaneously be offered the individualized optical correction of wavefront-guided (WFG) lenses and the superior comfort afforded by polymer coatings. This could be helpful to patients with ectasia suffering ocular dryness or dependent on scleral lenses for lengthy periods of wear.

PURPOSE

Wavefront-guided scleral lenses target lower- and higher-order aberrations of individual eyes using submicrometer-level contours in the anterior lens surface. Hydrophilic polyethylene glycol (PEG) polymer coatings applied to lens surfaces improve comfort and wettability. This study aimed to quantify aberration changes (e.g., masking) when applying polymer coatings to WFG and conventional scleral lenses.

METHODS

Two control lenses (remained uncoated) and 14 experimental lenses (two repeated builds of seven aberration designs: one spherical, two coma, four full WFG [second- to fifth-order aberrations]) were manufactured, and aberrations were measured (mean of three) by two operators before and after coating. Root mean square (RMS) and visual image quality (logVSX) differences were calculated for 6-mm diameters.

RESULTS

Median RMS aberration change due to coating was 0.012 μm (range, 0.008 to 0.057 μm). Maximum logVSX change due to coating was 0.073, predicting an approximately one letter change in acuity. Instrument sensitivity was 0.002 μm. Acute instrument and operator variabilities (standard deviations of individual [second- to fifth-order Zernikes] were all <0.027 μm). Longitudinal variability (control lenses) was low: all less than 0.017 μm. Although RMS of differences between repeated builds of all lenses was less than 0.25 D and not statistically significant, relatively, manufacture constituted the major variability, and RMS difference between repeated builds was at least four times greater than the effect of coating (median, 0.167 μm; range, 0.088 to 0.312 μm).

CONCLUSIONS

Application of polymer coatings caused measurable changes in aberrations of WFG and conventional scleral lenses; however, these were clinically and statistically insignificant and within variability of repeated lens manufacture. In their current states, WFG lenses and polymer coatings could be used simultaneously.

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.

Quantitative evaluation of visual function in patients with cornea verticillata associated with Fabry disease

PURPOSE

To evaluate the visual function of patients with cornea verticillata associated with Fabry disease through quantitative evaluations of contrast sensitivity function and straylight.

METHODS

We enrolled 28 eyes of 14 patients with Fabry disease (mean age, 37.1 ± 17.2  years) and 20 eyes of 20 age-matched healthy controls. Comprehensive ophthalmological examinations were performed and contrast sensitivity and letter contrast sensitivity were measured for all patients, following which the area under the log contrast sensitivity function (AULCSF) was calculated. Straylight was quantified using a straylight metre. Furthermore, subgroup analysis was performed according to the whorl-like pattern of cornea verticillata (mild and typical groups).

RESULTS

All 28 eyes showed cornea verticillata. Visual acuity and letter contrast sensitivity values were the same for normal eyes and those with Fabry disease. AULCSF differed by 0.15 log[s] between the eyes with Fabry disease and the control eyes (p < 0.001), while straylight differed by 0.45 log[s] between the two groups (p < 0.001). Subgroup analysis based on the whorl-like pattern of cornea verticillata showed that AULCSF and straylight differed by 0.11 log[s] and 0.08 log[s], respectively, between the typical and mild groups (p = 0.036 and p = 0.147, respectively).

CONCLUSION

Although cornea verticillata associated with Fabry disease does not affect the visual acuity and letter contrast sensitivity, more comprehensive testing of visual function by the inclusion of straylight and grating contrast sensitivity measurements shows clear functional deficits in these patients.

Assessment of straylight and the modulation transfer function of intraocular lenses with centrally localized opacification associated with the intraocular injection of gas

PURPOSE

To assess the optical quality of intraocular lenses (IOLs) explanted because of opacification after the intraocular injection of gas.

SETTING

David J. Apple Laboratory, Heidelberg, Germany.

DESIGN

Experimental study.

METHODS

Four hydrophilic acrylic IOLs were studied, each with a centrally localized round opacification pattern associated with the intraocular use of gas. Laboratory analysis included gross examination with a light microscope, followed by alizarin and von Kossa staining. Optical quality was assessed by examining the modulation transfer function (MTF) and straylight. Results were compared with those of a control IOL and normative data for straylight of the crystalline lens. The following parameters were derived from image analysis: opacified surface fraction, light loss in the opacified surface, and the area and number of granules. The relationship between straylight increase and those parameters was studied.

RESULTS

Fine granules were identified on the IOL surface and subsurface. The granules stained positive for calcium, and the MTF levels of 2 IOLs dropped markedly. The other 2 showed relatively minor changes. The straylight was extremely increased in 3 IOLs up to (and above) a level of that of a cataractous lens. A proportional relationship was found between straylight and the morphological parameters from image analysis.

CONCLUSIONS

Intraocular lenses with centrally localized opacification have a strong potential for deteriorating optical performance. However, the optical quality might differ depending on the morphology of opacification. A serious straylight increase was found in most of these IOLs, suggesting that affected patients may suffer from glare-related symptoms.

Quantitative Multiparameter Evaluation of Vacuoles in Intraocular Lenses Employing a High-Magnification Digital Microscopy Method

As small imperfections with micrometric sizes, fluid-filled vacuoles, also referred to as glistenings, in intraocular lenses (IOLs) have been known to induce significant unwanted light scattering that in several cases presumably cause complaints and sometimes lead to IOL explantation and replacement. This unwanted scatter is of particular concern for patients viewing bright light in reduced-light conditions such as when driving at night, as the scattered light toward the retina can cause temporary blindness. In this study, we have developed and implemented an accurate test methodology based on a high-magnification digital microscopy approach for quantitative multiparameter evaluation and classification of IOL vacuoles depending on their critical optical characteristics including vacuole size, density, shape, and orientation within the IOL material. Using the multiparameter database developed by evaluating vacuole characteristics, we established a classification grading system that can be used to evaluate vacuole effects on light scattering.

Quantifying the effect of straylight on photopic contrast sensitivity

The visual performance of a reference group (RG) using diffuser filters was compared to a cataract-diagnosed group (CatG). Measurements of straylight (SL) parameter, photopic contrast sensitivity (CS), and visual acuity (VA) were carried out in both groups. Before the analysis, the performance of the instruments used for this purpose was tested. The RG was comprised of three healthy, young eyes (25-30 years old) while 59 subjects (aged 50-80 years old) with lens opacities were recruited for the CatG. Six diffuser conditions were tested in the RG. To discriminate between light scattering levels, SL measurements proved to be most sensitive, VA did not discriminate at all, while CS showed intermediate sensitivity. VA was not correlated with SL, while the correlation between CS and SL was significant (p<0.05) in both groups. Since the correlation in the RG was particularly strong, parameters of a linear regression model are presented. The behavior of CS as a function of SL was comparable to some extent between RG and CatG.

Normative best-corrected values of the visual image quality metric VSX as a function of age and pupil size

The visual image quality metric the visual Strehl ratio (VSX) combines a comprehensive description of the optics of an eye (wavefront error) with an estimate of the photopic neural processing of the visual system, and has been shown to be predictive of subjective best focus and well correlated with change in visual performance. Best-corrected visual image quality was determined for 146 eyes, and the quantitative relation of VSX, age, and pupil size is presented, including 95% confidence interval norms for age groups between 20 and 80 years and pupil diameters from 3 to 7 mm. These norms were validated using an independently collected population of wavefront error measurements. The best visual image quality was found in young eyes at smaller pupil sizes. Increasing pupil size caused a more rapid decrease in VSX than increasing age. These objectively determined benchmarks represent the best theoretical levels of visual image quality achievable with a sphere, cylinder, and axis correction in normal eyes and can be used to evaluate both traditional and wavefront-guided optical corrections provided by refractive surgery, contact lenses, and spectacles.

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.