Retinal straylight and light distortion phenomena in normal and post-LASIK eyes

Post-refractive surgery of Israeli Defense Forces recruits in 2005-2018-prevalence, combat unit drop-out rates and utilization of eye-care services

PURPOSE

To assess the number of recruits for military service in the Israeli Defense Force (IDF) who underwent refractive surgery prior to enlistment and examine whether the procedure affected their ability to accomplish combat training.

SETTING

Medical records of IDF recruits.

DESIGN

Retrospective analysis of medical records of recruits with ametropia who underwent or did not undergo refractive surgery prior to enlistment.

METHODS

Recruits were categorized into ametropes and recruits who underwent refractive surgery. Fitness and assignment to combat units and completion status of combat training were compared between the two groups.

RESULTS

The study included 334,688 (182,969 males, 151,719 females) ametropes of which 5231 (4753 males, 478 females) underwent refractive surgery prior to recruitment. Refractive surgery prevalence increased from 9/1000 ametropes in 2005 to 18.5/1000 ametropes in 2018 (r = 0.912, p < 0.001); 2643 of the operated recruits (50.5%) had their surgery at the age of 17-18. Dropout rates from combat training were significantly lower in the refractive surgery group during the study period (1.68% vs. 6.14%, respectively, p < 0.001). Soldiers in the operated group were more frequently referred to ophthalmologists than those in the ametropes group and less frequently referred to optometrists.

CONCLUSIONS

The prevalence of refractive surgery in IDF recruits has increased substantially during the last decade with more of them applying to combat units. Refractive surgery opened new possibilities for recruits who were unfit for combat duty prior to surgery and did not appear to impair the chances of successfully completing combat training.

Forward-scattered and backward-scattered light in moderate keratoconus

INTRODUCTION

To evaluate the backscattered light, objective scatter index (OSI) and retinal straylight in patients with moderate keratoconus and healthy control subjects.

METHODS

A prospective observational study was developed with 33 patients in the moderate-keratoconus group (KC) and 34 in the non-keratoconus group (NKC). Corneal densitometry was obtained using Scheimpflug corneal tomography and measurements were expressed in grayscale units (GSU) over four zones within a 12.00 mm diameter around the corneal apex. A straylight meter was used to determine the amount of intraocular straylight under scotopic conditions, and the straylight parameter (LOG(s)) and test duration were recorded. The Optical Quality Analysis System based on the double-pass technique determined the OSI value.

RESULTS

Significant differences were observed between the KC and NKC groups for corneal densitometry (except in the 6-10 mm zone), OSI and retinal straylight. A moderate and significant correlation was found between OSI and retinal straylight LOG(s) (r = 0.52, p = 0.002). Weaker and non-significant correlations were found between corneal densitometry and the other parameters analysed (i.e., OSI, retinal straylight LOG(s) and retinal straylight times).

CONCLUSIONS

Backscattered light, retinal straylight and the OSI show clear differences between healthy eyes and those with moderate KC. The changes present in the stages of KC evaluated in the current study (stages II and III according to the Amsler-Krumeich classification) might alter the scattering of the light entering the eye.

Performance of a new device for the clinical determination of light discomfort

PURPOSE

To assess the performance of a new device for the clinical determination of light discomfort on a large sample of healthy human subjects.

METHODS

A total of 489 subjects ranging from 20 to 70 years old (241 men, 248 women) were evaluated with the LUMIZ™ 100 to determine light discomfort. Repeatability was assessed by means of within-subject standard deviation, coefficient of variation (CoV), and intraclass correlation coefficient (ICC). Repeated measures ANOVA, Kruskal-Wallis, and correlation analysis were applied to test for differences between repeated measures, and effect of age on reliability.

RESULTS

Discomfort thresholds obtained are well distributed across the light intensity range available (25 to 10211 lux). Intrasession ICCs are higher than 0.849 for all thresholds, and 85% of CoV are below 10%. Thresholds obtained in the first set of measurements are highly correlated with the median of three sets (r2 > 0.8). Intersession, 64% of CoV are below 10%. Age does not affect discomfort thresholds (p = 0.30), nor affect reliability (variance on CoV, p = 0.368).

CONCLUSIONS

The new device provides good intrasession repeatability for the clinical determination of light discomfort thresholds, although variance is slightly greater between sessions. The system is useful for the clinical determination of light discomfort.

Relationships Between Haloes and Objective Visual Quality in Healthy Eyes

Purpose

To determine the normal values and relationships between haloes and objective optical quality in healthy eyes.

Methods

In this cross-sectional study, haloes, pupillary responses to light, and objective optical quality were measured with the optical quality analysis system (OQAS) and a vision monitor (MonCv3) in 138 right eyes of 138 healthy young men with mean spherical equivalent of 0.32 ± 0.47 D.

Results

The mean disc halo size was 77.17 ± 25.03 arcmin. The mean objective optical quality values were as follows: objective scatter index (OSI), 0.58 ± 0.33; Strehl ratio (SR), 0.21 ± 0.05; modulation transfer function cutoff, 36.27 ± 7.98 cpd; OQAS value (OV)100%, 1.21 ± 0.27; OV20%, 0.91 ± 0.23; and OV9%, 0.59 ± 0.16. Disc halo size correlated independently with OSI (P < 0.001) and minimum pupil size (P = 0.003) by forward stepwise regression analysis (disc halo size = 16.60 + 26.24 × OSI + 11.34 × minimum pupil size; R² value = 17.7%; F = 14.52; P < 0.001).

Conclusions

Reference values for disc halo size and objective optical quality in healthy young subjects were established. Eyes with worse objective vision quality exhibited larger haloes.

Translational Relevance

The study provided the knowledge and the relationships of OQAS and halo measurements from a well-defined group of healthy young subjects. Both measurements are useful in clinical practice to help quantify the vision quality and complement each other.

Impact of Defocus and High-Order Aberrations on Light Disturbance Measurements

Purpose

To evaluate the impact of different levels of positive and negative defocus on light disturbance (LD) measures and to understand how high-order aberrations (HOAs) and topographic quality parameters may influence the perception of photic phenomena.

Methods

Thirty young healthy subjects (21 females and 9 males) attended this cross-sectional study. LD was evaluated with the light distortion analyzer (LDA) in natural accommodative and cycloplegic conditions with positive and negative induced defocus of 1.00D. HOAs were taken for a natural mesopic (without cycloplegia) and for fixed 5 mm (with cycloplegia) pupil size. The impact of corneal morphological parameters (SAI, SRI, and Q-value) in LD was also investigated.

Results

Positive and negative induced defocus of 1.00D significantly increased the size of LD (p < 0.010, Wilcoxon signed rank test) but not its irregularity index. Spherical-like HOAs were associated with the size of LD, while coma-like and total-like HOAs were associated with LD irregularity. Our results showed that SRI was significantly correlated with the size of the disturbance area (r=0.519, p=0.003, Spearman correlation) and SAI with both size (r=0.502, p=0.005, Spearman correlation) and irregularity (r=0.371, p=0.044, Spearman correlation). However, no correlation between the Q-value and LD parameters was found.

Conclusions

The uncorrected positive and negative refractive errors might increase the size of the LD, such as the spherical-like HOAs, SAI, and SRI, instead of asphericity. Coma-like and total-like HOAs and SAI may influence the perception of irregularities in the LD shape. These results might have an impact on postrefractive surgery visual performance that should be investigated.

Visual Outcomes and Higher Order Aberrations Following LASIK on Eyes with Low Myopia and Astigmatism

Background:

Laser-Assisted in situ Keratomileusis (LASIK) can induce corneal aberrations that can impact vision and patient satisfaction. Recent developments in laser technologies have helped minimise these aberrations.

Objective:

To assess the quality of vision and change in Higher-Order Aberrations (HOAs) following wavefront-optimized LASIK in low-myopic astigmatic patients.

Methods:

LASIK was performed on a total of 76 eyes in patients with myopia <4.0 D and cylinder <2.0 D using the WaveLight® EX500 excimer and FS200 femtosecond laser platform. Visual acuity, contrast sensitivity and HOAs were measured at 1 and 3 months postoperatively and compared to preoperative values. Subjective quality of vision was assessed pre- and postoperatively using a VF14 questionnaire.

Results:

Mean postoperative Spherical Equivalent (SE) was -0.09 ± 0.26 µm with 95% of patients within ± 0.5 D of attempted SE. Postoperative uncorrected distance visual acuity was 20/20 or better for 96% of patients. Contrast sensitivity increased against horizontal and vertical gratings at all spatial frequencies except for vertical gratings at 18 cycles/degree. Spherical aberration and total HOA increased by 0.085 µm and 0.13 µm respectively. The mean VF14 score increased from 89.2 ± 16.7% to 99 ± 1.4% postoperatively.

Conclusion:

LASIK performed using the WaveLight® EX500 excimer and WaveLight® FS200 laser platform provided improved contrast sensitivity and visual acuity with minimal introduction of HOAs, making it a suitable platform for low myopic astigmatic patients.

Minimum pupil in pupillary response to light and myopia affect disk halo size: a cross-sectional study

OBJECTIVES

To evaluate the relationship between pupillary response to light, myopia and disk halo size.

DESIGN

Cross-sectional study.

SETTING

Single refractive surgery centre.

PARTICIPANTS

In this study, 197 right eyes of 197 patients between 20 and 35 years of age were evaluated for disk halo size and pupillary response to light with a vision monitor.

PRIMARY AND SECONDARY OUTCOME MEASURES

Halo radius, age, spherical equivalent (SE), axial length (AL), initial diameter, amplitude of contraction, latency of contraction, duration of contraction, velocity of contraction, latency of dilation, duration of dilation, velocity of dilation, maximum pupil, minimum pupil, average pupil and dark pupil.

RESULTS

Significant associations were found between disk halo size and SE (r=-0.219, P=0.002), AL (r=0.152, P=0.033) and minimum pupil (r=0.149, P=0.037). There were no associations between disk halo size and initial diameter, amplitude of contraction, latency of contraction, duration of contraction, velocity of contraction, latency of dilation, duration of dilation, velocity of dilation, maximum pupil, average pupil, dark pupil and age (P>0.05). A significant difference in disk halo size was detected between the low-moderate and high myopia (SE< -6 D) groups (P=0.002) and between the small and large (minimum pupil≥4 mm) minimum pupil size groups (P=0.014).

CONCLUSIONS

Patients with a high SE and large minimum pupil size (minimum pupil ≥4 mm) suffered more disability glare than those with a low SE and small minimum pupil size.

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.

Study of light scattering using C-Quant® in patients with Fuchs' endothelial dystrophy: A pilot study

OBJECTIVE

The purpose of this study was to determine the light scattering in patients with Fuchs' endothelial dystrophy without clinically significant corneal oedema, and evaluate its relationship with endothelial cell count, corneal thickness, and corneal biomechanical parameters.

MATERIALS AND METHODS

The values of light scattering were measured by C-Quant^® (Oculus Optikgeräte GmbH, Germany) in 32 eyes of 17 patients diagnosed with Fuchs' endothelial dystrophy without clinically significant corneal oedema. Corneal biomechanical properties were determined using ORA (ocular response) and Corvis ST^® (tonometry).

RESULTS

A light scattering value outside the normal range was observed in 93.8% of eyes studied. No statistically significant association (P>.05) was found between the values of the measured light scattering by C-Quant^® and endothelial count, pachymetry, or corneal biomechanical properties.

CONCLUSIONS

In this study, changes were found in the values of light scattering values of patients with corneal Fuchs' endothelial dystrophy. This change does not appear to correlate significantly with disease severity.

Assessment of subjective intraocular forward scattering and quality of vision after posterior chamber phakic intraocular lens with a central hole (Hole ICL) implantation

PURPOSE

To evaluate the subjective intraocular forward scattering and quality of vision after posterior chamber phakic intraocular lens with a central hole (Hole ICL, STAAR Surgical) implantation.

METHODS

We prospectively examined 29 eyes of 29 consecutive patients (15 men and 14 women; ages, 37.2 ± 8.8 years) undergoing Hole ICL implantation. We assessed the values of the logarithmic straylight value [log (s)] using a straylight meter (C-Quant^™ , Oculus) preoperatively and 3 months postoperatively. The patients completed a questionnaire detailing symptoms on a quantitative grading scale (National Eye Institute Refractive Error Quality of Life Instrument-42; NEI RQL-42) 3 months postoperatively. We compared the preoperative and postoperative values of the log(s) and evaluated the correlation of these values with patient subjective symptoms.

RESULTS

The mean log(s) was not significantly changed, from 1.07 ± 0.20 preoperatively, to 1.06 ± 0.17 postoperatively (Wilcoxon signed-rank test, p = 0.641). There was a significant correlation between the preoperative and postoperative log(s) (Spearman's correlation coefficient r = 0.695, p < 0.001). The postoperative log(s) was significantly associated with the scores of glare in the questionnaire (Spearman's correlation coefficient r = -0.575, p = 0.017).

CONCLUSIONS

According to our experience, Hole ICL implantation does not induce a significant additional change in the subjective intraocular forward scattering. The symptom of glare after Hole ICL implantation was significantly correlated with the postoperative intraocular forward scattering in relation to the preoperative one.

Short-term changes in light distortion in orthokeratology subjects

Purpose. Quantifying adaptation to light distortion of subjects undergoing orthokeratology (OK) for myopia during the first month of treatment. Methods. Twenty-nine healthy volunteers (age: 22.34 ± 8.08 years) with mean spherical equivalent refractive error −2.10 ± 0.93D were evaluated at baseline and days 1, 7, 15, and 30 of OK treatment. Light distortion was determined using an experimental prototype. Corneal aberrations were derived from corneal topography for different pupil sizes. Contrast sensitivity function (CSF) was analyzed for frequencies of 1.50, 2.12, 3.00, 4.24, 6.00, 8.49, 12.00, 16.97, and 24.00 cpd under photopic conditions. Results. Average monocular values of all light distortion parameters measured increased significantly on day 1, returning to baseline after 1 week (P < 0.05 in all cases). Spherical-like aberration stabilized on day 7 for all pupil diameters, while coma-like for smaller pupils only. CSF was significantly reduced on day 1 for all spatial frequencies except for 1.5 cpd, returning to baseline afterwards. Significant correlation was found between light distortion and contrast sensitivity for middle and high frequencies (P < 0.05) after 15 days. Conclusion. Despite consistently increased levels of corneal aberrations, light distortion tends to return to baseline after one week of treatment, suggesting that neural adaptation is capable of overcoming optical quality degradation.

Relationship between halo size and forward light scatter

PURPOSE

To determine the relationship between the size of a halo induced by a glare source and forward scatter or visual acuity (VA) in healthy eyes.

METHOD

Measurements were made in the right eyes of 51 healthy individuals of mean age 29.3 ± 7.5 years. Halo radius was measured using the Vision Monitor and low luminance (1 cd/m(2)) optotypes presented at a distance of 2.5 m. The visual angle subtended by the radius of the halo was calculated in minutes of arc (arc min). Forward scatter or, straylight, was measured using the compensation comparison technique. Best-corrected distance VA was measured using high contrast (HC) (96%) and low contrast (LC) (10%) Bailey-Lovie logMAR letter charts under photopic (85 cd/m(2)) and mesopic (0.15 cd/m(2)) luminance conditions.

RESULTS

Mean halo radius was 202 ± 43 arc min (3.4 ± 0.7°) and mean retinal straylight was 0.95 ± 0.12 log units. Mean photopic distance HC-VA and LC-VA were -0.02 ± 0.06 and 0.12 ± 0.09 logMAR, respectively. Mean mesopic distance HC-VA and LC-VA were 0.35 ± 0.11 and 0.74 ± 0.11 logMAR, respectively. Forward stepwise regression analysis revealed that halo radius was significantly correlated with straylight (r=0.45) and mesopic LC-VA (r=0.48), but not with photopic HC-VA and/or LC-VA and mesopic HC-VA.

CONCLUSIONS

In healthy eyes, the larger the halo size induced by a given glare source, the greater the forward-scatter (straylight) and worse the mesopic LC-VA. Halo size seems to be independent of photopic HC-VA or LC-VA and mesopic HC-VA.

Normal values for the size of a halo produced by a glare source

PURPOSE

To determine the size of a halo in the visual field induced by bright light in healthy eyes of all ages using the Vision Monitor (MonCv3; Metrovision, Pérenchies, France) and to assess the repeatability of the method.

METHODS

Measurements were made in the right eyes of 147 healthy subjects (mean age: 48.2 ± 16.2 years) who were classified into six age groups. Using the Vision Monitor, optotypes of low luminance were presented at a distance of 2.5 m. The visual angle subtended by the radius of the halo was calculated in minutes of arc (arc min). The repeatability of the method was determined in a subset of 37 subjects older than 50 years by calculating the Bland-Altman coefficient of repeatability.

RESULTS

The mean radius of the halo was 111.6 ± 39.8 arc min. Halo radius started to increase significantly from the age of 50 to 59 years. The relationship between halo radius and age (r = 0.65; P < .0001) was described by fitting a power function to the data. Halo size was independent of gender. The coefficient of repeatability of the method was ±44 arc min.

CONCLUSIONS

Halo size increases with age following a power model. The normal halo size values provided could help clinicians distinguish between normal or abnormal glare problems. The intersession repeatability observed for halo size measurement indicates this method could be useful for assessing visual impairment caused by glare.

History of ocular straylight measurement: A review

The earliest studies on 'disability glare' date from the early 20(th) century. The condition was defined as the negative effect on visual function of a bright light located at some distance in the visual field. It was found that for larger angles (>1 degree) the functional effect corresponded precisely to the effect of a light with a luminosity equal to that of the light that is perceived spreading around such a bright source. This perceived spreading of light was called straylight and by international standard disability glare was defined as identical to straylight. The phenomenon was recognized in the ophthalmological community as an important aspect of the quality of vision and attempts were made to design instruments to measure it. This must not be confused with instruments that assess light spreading over small distances (<1 degree), as originating from (higher order) aberrations and defocus. In recent years a new instrument has gained acceptance (C-Quant) for objective and controllable assessment of straylight in the clinical setting. This overview provides a sketch of the historical development of straylight measurement, as well as the results of studies on the origins of straylight (or disability glare) in the normal eye, and on findings on cataract (surgery) and corneal conditions.