Intraocular Light Scatter Research Articles

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

PurposeThe 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.MethodsRecognition 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).ResultsFoveal 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.ConclusionsRecognition 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 RelevanceThe 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.

Induced glare testing — an underutilized test in evaluating visual disability in patients presenting with symptomatic cataracts

Background: Cataract increases intraocular light scatter which affects the retinal image contrast and sensitivity. Symptomatic patients with cataract complain of a drop in the quality of vision or glare affecting daily routine even with preserved visual acuity. This study was aimed to quantify the drop in the glare induced visual acuity (VA) and contrast sensitivity (CS) in different morphological types of cataracts. Material and methods: This was an observational study on a prospective cohort, conducted at a tertiary-care centre in South-India. Patients admitted for cataract surgeries between March and September 2017 with BCVA ≥ 6/60 (Snellen) and ≥ 40 years were enrolled. LogMAR VA and CS were measured pre and post-operatively, with and without glare induction using brightness acuity tester. Patients were sub-categorised based on morphology and the presence of glare as a symptom. Paired-t test for the pre- and post-operative values and analysis with Bonferroni’s adjustment were the statistical methods used. Results: Data of 78 patients were sub-categorised and analysed. Glare induction with high glare was significant in all the studied groups. LogMAR VA was affected most in group 3 (0.20, 10 letters, p < 0.05) and the CS in group 2 (0.62, 4.1 step drop, p < 0.05). Patients who had glare as a symptom had an average greater drop in LogMAR VA (0.30, p = 0.01) and CS (–0.29, p = 0.03) when induced with a high glare. Conclusions: All morphological types of cataracts affect VA and CS to a greater extent in conditions of bright lighting. Glare induced VA and CS testing is a sensitive and an adjunct tool to traditional high contrast VA testing, in evaluating the visual dysfunction of patients presenting with symptomatic cataracts.

Intraocular Light Scatter in Eyes With the Boston Type 1 Keratoprosthesis.

The Boston keratoprosthesis (KPro) is the most commonly used artificial cornea. It has been proven to be successful for severe corneal disease not amenable to keratoplasty. We have observed our patients reporting debilitating glare despite attaining good visual acuities. This motivated us to objectively measure light scatter in eyes with a KPro. Light scatter was measured in 21 eyes with the Boston type 1 KPro with a VA of 20/150 or better and was compared with 13 healthy control eyes using the Oculus C-Quant device (Arlington, WA). Eyes were also measured using an occluder contact lens. Light scatter (quantified as the logS value) was significantly higher in the KPro group than in the control (2.34 ± 0.15 vs. 1.29 ± 0.17, P < 0.001). The polymethylmethacrylate (PMMA) KPro group (16 eyes, logS 2.49 ± 0.19) but not the titanium group (5 eyes, logS 1.87 ± 0.15) had significantly higher light scattering than the control. The use of an occluder contact lens significantly decreased light scatter in eyes with a PMMA backplate (n = 11, logS 1.71 vs. 2.42, P = 0.028). This study confirms that intraocular light scatter is increased in KPro eyes. Possibly because of its opaque nature, the titanium backplate model seems to produce less light scatter than does the PMMA model. Occluder contact lenses reduced light scatter significantly in the PMMA KPro and could be a treatment option for symptomatic patients.

Intraocular light scatter in patients on topical intraocular pressure-lowering medication.

To quantify ocular light scattering in patients under treatment with intraocular pressure-lowering eye-drops. In this prospective, observational, cross-sectional case series study, 160 eyes of 160 patients with primary open angle glaucoma or primary ocular hypertension were consecutively recruited from our Glaucoma Department over 7 months. In total, 46 eyes of 46 healthy volunteers matched for age and sex served as the control group. The variables recorded in a single visit were as follows: drug and number of drops per day, treatment duration, OXFORD corneal staining grade, lower tear meniscus height as measured by spectral domain optical coherence tomography, ocular redness and non-invasive tear breakup time measured with the Oculus Keratograph 5M, ocular surface disease index questionnaire score and objective scatter index through a double-pass technique (Optical Analysis System II). Objective scatter index was higher in the patient group (3.1, interquartile range = 1.8-5.47) than in the control group (1.95; interquartile range = 0.7-5; p = 0.017). In a multiple linear regression model, non-invasive tear breakup time was identified as the most influential variable on light scatter (mean ratio = -1.015; p = 0.003; 95% confidence interval = -1.025 to -1.005). No correlation with objective scatter index was observed for number of daily eye-drops, preservative concentration or treatment duration. Participants on anti-glaucoma medication showed a significantly higher objective scatter index than control group individuals. In the treated patient group, a lower non-invasive tear breakup time was associated with a higher objective scatter index. This suggests that lubricating eye-drops to improve tear breakup time could also improve vision quality in these patients by diminishing light scattering.

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

Much knowledge has been collected over the past 20years 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. 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.

The impact of dysfunctional tear films and optical aberrations on chronic migraine

BackgroundMigraine is a multifactorial disorder with complex neuronal and vascular mechanisms that encompasses a wide clinical spectrum of symptoms, including ocular manifestations. Dry eye disease and dysfunction of ocular somatosensory pathways have been implicated in the pathogenesis. The current study investigates the association between a dysfunctional tear film and ocular aberrations with migraine.MethodsSixty eyes of 30 patients with migraine and 60 eyes of 30 controls were studied. Dry eye evaluation included Schirmer’s test, tear film break-up time, corneal esthesiometry and lipid layer analysis using Lipiview® interferometer. Wavefront aberrations were measured using Optical Path Difference before performing the dry eye evaluation. The intraocular light scatter was quantified using the objective scatter index (OSI) of the optical quality analysis system. Measured parameters were compared between the migraine and the control group using independent sample t-test. Statistical analysis was performed using commercial software. A p value of ≤ 0.05 was considered statistically significant.ResultsThere were 19 females and 11 males in each group. Statistically significant difference was found between the two groups with respect to total aberrations (p = 0.049), higher order aberrations (p = 0.009), coma (p = 0.03), spherical aberrations (p = 0.018), Lipiview interferometric coloric units (p < 0.001) and OSI (p < 0.001). Trefoil (p = 0.26) and TBUT (p = 0.398) were not significantly different between both groups.ConclusionsOcular aberrations are higher in patients with migraine as compared with controls. Tear film abnormalities add to the aberrations in otherwise asymptomatic patients and may also be associated with migraineous attacks. Treating the ocular surface to obtain a healthy tear film might introduce a potential modifiable factor in the prevention of migraneous attacks.

Evaluation of Visual Quality in Patients With Fuchs Endothelial Corneal Dystrophy.

Fuchs endothelial corneal dystrophy (FECD) is a bilateral corneal endothelial dystrophy characterized by the deposition of extracellular matrix (guttae), thickening of Descemet membrane, and progressive loss of corneal endothelial cells. Progressive endothelial cellular loss leads to corneal edema and impairs visual function. In eyes with FECD, corneal edema begins in the central cornea and expands into the periphery. FECD is the most common dystrophic reason for corneal transplantation in many countries. Some patients with FECD report visual discomfort despite the absence of corneal edema. Intraocular forward light scatter impairs patients' quality of vision (QOV), and corneal guttae associated with FECD may cause intraocular light scatter and glare, which can be extremely debilitating despite the absence of edema. We recently investigated the effect of the severity of corneal guttae on QOV in patients with mild FECD. It was shown that corneal guttae increased forward light scatter that negatively affected QOV in eyes with mild FECD without severe corneal edema. Therefore, quantification of corneal guttae would be useful to determine surgical indications for eyes with mild FECD. This review discusses QOV in patients with FECD.

Google Glass Glare: disability glare produced by a head-mounted visual display.

Head mounted displays are a type of wearable technology - a market that is projected to expand rapidly over the coming years. Probably the most well known example is the device Google Glass (or 'Glass'). Here we investigate the extent to which the device display can interfere with normal visual function by producing monocular disability glare. Contrast sensitivity was measured in two normally sighted participants, 32 and 52 years of age. Data were recorded for the right eye, the left eye and then again in a binocular condition. Measurements were taken both with and without the Glass in place, across a range of stimulus luminance levels using a two-alternative forced-choice methodology. The device produced a significant reduction in contrast sensitivity in the right eye (>0.5 log units). The level of disability glare increased as stimulus luminance was reduced in a manner consistent with intraocular light scatter, resulting in a veiling retinal illuminance. Sensitivity in the left eye was unaffected. A significant reduction in binocular contrast sensitivity occurred at lower luminance levels due to a loss of binocular summation, although binocular sensitivity was not found to fall below the sensitivity of the better monocular level (binocular inhibition). Head mounted displays such as Google Glass have the potential to cause significant disability glare in the eye exposed to the visual display, particularly under conditions of low luminance. They can also cause a more modest binocular reduction in sensitivity by eliminating the benefits of binocular summation.

Effect of Rebamipide Ophthalmic Suspension on Intraocular Light Scattering for Dry Eye After Corneal Refractive Surgery.

To assess the changes in intraocular scattering before and after instillation of rebamipide ophthalmic suspension in patients with dry eye after corneal refractive surgery. This study enrolled 60 eyes of 30 dry eye patients undergoing corneal refractive surgery. Patients were randomly assigned to start topical administration of rebamipide ophthalmic suspension (rebamipide group) or artificial tears (control group) 4 times daily for 4 weeks. Tear secretion, tear break-up time (TBUT), and the fluorescein score were measured before and after treatment. Intraocular light scattering was also measured as the objective scattering index (OSI) at 0.5-second intervals over 10 seconds. In the rebamipide group, the Schirmer I test, TBUT, and fluorescein score improved significantly, from 11.4 ± 9.0 mm, 2.2 ± 0.7 seconds, and 4.3 ± 1.3 to 14.9 ± 7.4 mm, 4.5 ± 1.7 seconds, and 1.9 ± 1.0, respectively (P = 0.006, P < 0.001, P < 0.001, Wilcoxon signed rank test). We found significant improvements in OSI at 5.0 to 10.0 seconds after blinking (5-8 seconds, P = 0.01; 9 seconds, P = 0.02; 10 seconds, P < 0.001). The mean OSI, the OSI change rate, and the OSI slope of the linear regression line improved significantly, from 2.73 ± 1.52, 74.7 ± 69.5%, and 0.10 ± 0.12 to 2.19 ± 1.19, 28.6 ± 48.7%, and 0.04 ± 0.08, respectively (P = 0.02, 0.003, and 0.03). Rebamipide ophthalmic suspension was effective for improving both ocular surface parameters and optical quality in patients with dry eye undergoing corneal refractive surgery, suggesting that it may hold promise for the treatment of such patients.

Relationship between Corneal Guttae and Quality of Vision in Patients with Mild Fuchs' Endothelial Corneal Dystrophy

To investigate the effect of the severity of corneal guttae on quality of vision (QOV) in patients with mild Fuchs' endothelial corneal dystrophy (FECD). Cross-sectional study. Twenty-three eyes of 14 patients with mild FECD without corneal edema on slit-lamp examination (5 pseudophakic eyes and 18 phakic eyes with mild lens opacity; grade 1.0-2.0 nuclear opalescence, grade 1.0-2.0 nuclear color, grade 1.0 cortical cataract, and grade 1.0 posterior subcapsular cataract on the Lens Opacities Classification System, version III). The area ratio of the corneal guttae (ARCG) in the endothelial cells was measured by multifocal specular microscopy. The QOV parameters, that is, corrected distance visual acuity (CDVA), letter contrast sensitivity (LCS), and intraocular straylight, also were measured. The correlations were assessed between the ARCG and QOV parameters and between the straylight and CDVA and LCS. The ARCG, logarithm of the minimum angle of resolution CDVA, LCS, and straylight. Univariate analysis showed that the ARCG was correlated significantly with the CDVA, LCS, and straylight (R(2) = 0.41, P = 0.001; R(2) = 0.55, P = 0.001; and R(2) = 0.39, P = 0.002, respectively). Univariate analysis also showed that straylight was correlated significantly with the CDVA and LCS (R(2) = 0.47, P = 0.001 and R(2) = 0.41, P = 0.001, respectively). Corneal guttae without edema caused the QOV to deteriorate in eyes with FECD. Patients with higher straylight had worse CDVA or LCS. Intraocular forward light scatter caused by corneal guttae may result in visual disturbances. Quantification of corneal guttae can be useful to evaluate the effect of guttae on the QOV and determine the surgical indications of endothelial keratoplasty for eyes with mild FECD.

Enhanced Text Spacing Improves Reading Performance in Individuals with Macular Disease

The search by many investigators for a solution to the reading problems encountered by individuals with no central vision has been long and, to date, not very fruitful. Most textual manipulations, including font size, have led to only modest gains in reading speed. Previous work on spatial integrative properties of peripheral retina suggests that ‘visual crowding’ may be a major factor contributing to inefficient reading. Crowding refers to the fact that juxtaposed targets viewed eccentrically may be difficult to identify. The purpose of this study was to assess the combined effects of line spacing and word spacing on the ability of individuals with age-related macular degeneration (ARMD) to read short passages of text that were printed with either high (87.5%) or low contrast (17.5%) letters. Low contrast text was used to avoid potential ceiling effects and to mimic a possible reduction in letter contrast with light scatter from media opacities. For both low and high contrast text, the fastest reading speeds we measured were for passages of text with double line and double word spacing. In comparison with standard single spacing, double word/line spacing increased reading speed by approximately 26% with high contrast text (p < 0.001), and by 46% with low contrast text (p < 0.001). In addition, double line/word spacing more than halved the number of reading errors obtained with single spaced text. We compare our results with previous reading studies on ARMD patients, and conclude that crowding is detrimental to reading and that its effects can be reduced with enhanced text spacing. Spacing is particularly important when the contrast of the text is reduced, as may occur with intraocular light scatter or poor viewing conditions. We recommend that macular disease patients should employ double line spacing and double-character word spacing to maximize their reading efficiency.

The relationship between halo size and intraocular light scatter in normal healthy subjects

AbstractPurpose To determine the relationship between the size of a halo in the visual field induced by bright light and the intraocular light scatter in normal healthy eyes.Methods Measurements were made in the right eyes of 66 healthy subjects (mean age 33 ± 9 years). Using the Vision monitor, optotypes of low luminance (1 cd/m2) 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). Retinal straylight was measured with the compensation comparison technique. Best‐corrected distance visual acuity (BCVA) was evaluated with logMAR Bailey‐Lovie letter charts.Results The mean radius of the halo was 199.3 ± 45.6 arc min, mean retinal straylight was 0.98 ± 0.13 log units and mean BCVA was ‐0.02 ± 0.07 logMAR. There was a significant positive correlation between halo radius and straylight (r = 0.32, p &lt; 0.01) and between halo radius and BCVA (r = 0.36, p &lt; 0.01). However, no significant relationship was found between retinal straylight and BCVA.Conclusion Higher intraocular light scatter levels were related to larger halo size in healthy human eyes.

The impact of cataract on the quantitative, non-invasive assessment of retinal blood Flow

The aim of the study was to determine the impact of cataract on the quantitative, non-invasive assessment of retinal blood flow assessed by bidirectional laser Doppler flowmetry and simultaneous vessel densitometry. Ten patients scheduled for extracapsular cataract extraction using phacoemulsification and intraocular lens implantation between the ages of 61 and 84 (mean age 73 years, SD ± 8) were prospectively recruited. Two visits were required to complete the study; one visit prior to extracapsular cataract extraction and one at least 6 weeks after the surgery to allow for sufficient postoperative recovery. The severity of cataract was documented using the Lens Opacity Classification System (LOCS, III) at the first visit. Retinal arteriolar hemodynamics were measured at both visits using the high-intensity setting of the Canon Laser Blood Flowmeter. All eyes showed no clinical signs of postoperative intraocular inflammation. The quantitative assessment of retinal arteriolar diameter and blood flow were reduced following extracapsular cataract extraction (Wilcoxon signed-rank test, p = 0.022 and p=0.028, respectively); however, centreline blood velocity was not significantly changed (Wilcoxon signed-rank test, p=0.074). Intraocular pressure was unchanged pre- and postcataract extraction. Retinal vessel densitometry assessment in the presence of cataract results in the erroneous elevation of the diameter measurement and thereby the calculation of blood flow. The bidirectional Doppler assessment of blood velocity appears to be more robust to light scatter induced by cataract. Care needs to be exercised in the interpretation of studies of retinal vessel diameter or blood flow that utilize similar densitometry techniques.

Visual acuity and contrast sensitivity after posterior lamellar keratoplasty

It has previously been reported that patients who suffer from Fuchs' endothelial dystrophy (Fuchs' ED) have decreased contrast sensibility threshold. The removal of endothelial guttata by Descemet's Stripping Automated Endothelial Keratoplasty (DSAEK) surgery has also been demonstrated to decrease intraocular light scatter and improve contrast thresholds. The purpose of this study was to compare different visual qualities in patients that had undergone DSAEK surgery in one eye while having untreated Fuchs' dystrophy in the other eye. Thirty-two eyes of 16 patients with bilateral Fuchs' ED who had DSAEK surgery performed in one eye were enrolled. Visual acuity at 100% contrast and contrast sensitivity (CS) as evaluated by a modified simulation of the Freiburg Acuity and Contrast Test, was measured in both eyes of each patient. Snellen visual acuity improved in treated eyes from 0.66 ± 0.35 (SD) before surgery to 0.38 ± 0.18 after surgery (log MAR units; p < 0.01). In eyes with untreated Fuchs' dystrophy, visual acuity was 0.46 ± 0.14. In a pairwise comparison, there was no difference in Snellen visual acuity between treated and nontreated eyes (p = 0.12). Contrast sensitivity was significantly better in DSAEK-treated eyes compared with untreated eyes. Mean log CS in DSAEK-treated eyes was 1.06 ± 0.25 compared with a mean log CS of 0.84 ± 0.16 in untreated eyes (p < 0.01). Fourteen of 16 patients (88%) reported that vision in their DSAEK-treated eye had the best visual quality. In this study, using a paired design, we demonstrate improved CS in DSAEK-operated eyes when compared with the other eye that had untreated Fuchs' ED despite the fact that no difference in visual quality was detected with standard Snellen visual acuity. Contrast sensitivity appears to be superior to normal visual acuity measurements in the evaluation of overall visual quality after DSAEK.

Forward light scatter and contrast sensitivity in keratoconic patients

The aim of this study was to obtain intraocular forward light scatter (FLS) data in keratoconus patients and to explore possible relationships with contrast sensitivity. Intraocular straylight was assessed in the right eye of 10 visually-normal subjects (31±5 years) and 5 keratoconus patients (34±9 years) using the van den Berg straylight meter. Contrast sensitivity was also measured in both groups, with and without a glare source provided by the Brightness Acuity Tester (BAT), using a Pelli-Robson chart. Inclusion criteria for the keratoconic patients were chosen to avoid natural causes of increased scatter and to limit the influence of factors that could affect the straylight measurements. Intraocular light scatter was significantly greater in the keratoconic patients than in normal subjects for each of the three eccentricities tested (Mann-Whitney U test (2-tailed): Z≤-2.2, p≤0.027). Baseline Pelli-Robson contrast sensitivity was also found to be lower in the keratoconus group than in the normal subjects (Mann-Whitney U test: Z=-2.2, p=0.023). Under glare conditions contrast loss was significantly greater in the keratoconic patients than in the normal subjects (Mann-Whitney U test: Z=-2.5, p=0.013). High levels of negative correlation were found between the magnitudes of intraocular straylight and baseline contrast sensitivity in the keratoconus group (Spearman's correlation coefficient (RS)≤-0.87, p≤0.027). The high values of straylight measured in the keratoconic patients cannot be explained by age or scarring and could be related to the structural degradation of the cornea. Further investigation of intraocular scatter in keratoconus is warranted to improve our current understanding of the visual deficits associated with this pathology.

Glistenings on Intraocular Lenses in Healthy Eyes: Effects and Associations

To assess glistenings in AcrySof (Alcon Laboratories Inc) intraocular lenses (IOLs), to quantify any effects of glistenings on the visual function of patients with healthy eyes, and to investigate whether glistenings were associated with demographic or lens characteristics. Case files from a consecutive series of healthy eyes were retrospectively analyzed. Subjective glistening grades were investigated for associations with the following parameters: contrast sensitivity, corrected distance visual acuity (CDVA), intraocular light scattering (measured by C-Quant [Oculus Optikgeräte GmbH]), posterior capsule opacification, demographic characteristics, lens power, and duration of pseudophakia. The subjective grading method was compared to objective software-based quantitation of glistenings. The study cohort included 97 eyes from 65 patients with a mean age of 65 ± 11 years. Mean follow-up was 18 ± 17 months. Glistening grades did not vary by duration of pseudophakia (P=.19), although study design limited confidence in this result. Glistening grades had no associations with lens power (P=.41), intraocular light scattering (P=.31), logMAR CDVA (P=.64), contrast sensitivity at any spatial frequency (all P ≥.22), or with any other parameter under investigation. The software-based assessment confirmed the validity of the subjective grading method: glistening grades correlated with vacuoles/mm(2) (P<.0001) and mean values for vacuoles/mm(2) were statistically significant for each glistening grade (all P ≤.004). In healthy eyes, glistening grade was not associated with contrast sensitivity, CDVA, intraocular light scatter, or any lens or demographic characteristics that were investigated.

Is foveal thickness correlated with macular pigment optical density and with Intraocular light scatter in early age‐related maculopathy?

Abstract Purpose The purpose of this study was to investigate the relationship of foveal thickness with macular pigment optical density (MPOD) and intraocular light scatter (IOLS) in Early Age Related Maculopathy (ARM) subjects. Methods Forty eyes of adults (age mean: 65 ± 7 years) with early Age Related Maculopathy (ARM) were investigated. All patients had undergone a complete ophthalmic examination to select the subjects. Foveal thickness parameters were obtained using optical coherence tomography (OCT: Topcon 3D OCT‐1000). Macular pigment optical density at the fovea was measured with the Metropsis Test (Cambridge Research Systems. Ltd. UK) and intraocular light scatter was measured using the C‐Quant straylight meter (Oculus AG, Germany). Results Mean foveal thickness was 226.44 ± 22.56 microns, mean MPOD was 0.22 ± 0.29 log units and mean IOLS was 1.14 ± 0.18 log units. With the regression analysis of linear model, we did not find a significant correlation between foveal thickness and MPOD and neither between foveal thickness and IOLS in early ARM subjects. Conclusion No correlation was found between foveal thickness and macular pigment optical density and between foveal thickness and intraocular light scatter in early ARM subjects.

The fundamentals of visual acuity measurement

Abstract Purpose To provide the background to the symposium on visual acuity and its measurement Methods The parameters employed to quantify visual performance will be defined. Commonly used measurement techniques ranging from traditional letter charts to psychophysical computer‐based programmes, will be described and compared, with reference to the peer‐reviewed literature in this area. The issues of accuracy and repeatability will be considered in the context of the clinical setting and scientific studies. Results Letter charts are most commonly employed to assess visual performance because of their ease of use for both the patient and assessor, but they suffer from design limitations. Psychophysical procedures are more flexible and can improve repeatability, but are time consuming and fatigue can start to play a part. Such techniques are generally more suited to the research environment. High contrast visual acuity measurement can give a misleading impression regarding the quality of vision. This is particularly the case for subjects with impaired optical quality relating to an increase in intraocular light scatter and/or increased higher order aberrations. Assessment in the contrast domain is essential to build up a fuller picture. Conclusion The assessment of visual quality requires an understanding of test design and limitations. The method used should be chosen to suit the aims of the work and partly depends on whether it is taking place in a clinical practice setting or as part of a research study.

Reflections on blindsight: Neuroimaging and behavioural explorations clarify a case of reversed localisation in the blind field of a patient with hemianopia.

Blindsight refers to residual visual abilities of patients with primary visual cortex lesions. Most of this research uses single case studies, most famously patient GY. We examined a patient (DC) after surgical resection of V1 who demonstrated robust but reversed blind field target localisation, mislocalising midline blind field targets to the periphery and vice versa. This pattern was reliable across multiple sessions and was not because of extraocular light scatter. We then used functional magnetic resonance imaging to examine neural responses to blind field motion stimuli with no evidence of motion-selective activation in DC's extrastriate cortex in the damaged hemisphere, in stark contrast to GY who showed robust bilateral activation in response to blind field stimuli. This suggests that DC's blind field performance may not represent true blindsight. Follow-up testing with the target--background contrast reversed (i.e., black targets/white background), eliminated DC's reversed localisation, strongly suggesting that she was employing an unusual decision criterion based on intraocular light scatter. DC's failure to demonstrate true blindsight may be related to the age at which she acquired her lesion--much later in life than GY.

The Effect of Corneal Light Scatter on Vision After Descemet Stripping With Endothelial Keratoplasty

To establish an association between corneal light scatter and vision after Descemet stripping with endothelial keratoplasty (DSEK). Twenty eyes of patients with Fuchs endothelial dystrophy were examined before and at 1, 3, and 6 months after DSEK in a prospective study. Main outcome measures were high-contrast best-corrected visual acuity, intraocular forward light scatter, and corneal backscatter. One eye was excluded because of endothelial graft failure within 1 month. Best-corrected visual acuity improved at 3 months after DSEK (mean [standard deviation], 0.31 [0.20] logarithm of the minimum angle of resolution [logMAR]; Snellen equivalent, 20/41) relative to before DSEK (0.46 [0.26] logMAR; Snellen equivalent, 20/58; P = .03). Posterior corneal backscatter decreased 1 month after DSEK (P < .001), but backscatter from the anterior, middle, and posterior cornea did not return to normal by 6 months (P < or = .02). At 6 months, best-corrected visual acuity correlated with recipient age (r = 0.84, P < .001) and with intraocular forward light scatter (r = 0.67, P < .001); forward light scatter also correlated with recipient age (r = 0.67, P < .001). Six months after DSEK, corneal light scatter remained greater in eyes with Fuchs endothelial dystrophy than in normal eyes and correlated with recipient age and visual acuity. Recipient age might be the best preoperative predictor of vision after DSEK.