Binocular contrast inhibition in subjects with age-related macular degeneration

Biofeedback rehabilitation in patients with binocular inhibition due to macular disease

BACKGROUND

To investigate whether patients with binocular reading inhibition due to central vision loss benefit from a new biofeedback (BF) rehabilitation method that aimed at improving fixation stability and at establishing a correspondence between the monocular preferred retinal loci (PRLs) on functioning retina in both eyes.

METHODS

Thirty-three patients with bilateral macular disease and with binocular reading inhibition participated in 10 training sessions consisting of 10-min visual stimulation for each eye to stabilize fixation and relocate the PRL (if needed) using the BF module of the MP-1 microperimeter (Nidek Technologies Srl., Vigonza, PD, Italy). Binocular and monocular reading performance, contrast sensitivity, and visual acuity were evaluated pre and post training. Binocular summation/inhibition was evaluated with binocular ratio (BR).

RESULTS

Fixation stability improved significantly post training in both eyes. Maximum reading speed during binocular viewing increased from 57 ± 24wpm pre training to 67 ± 24wpm post training. BR increased for all parameters of reading, visual acuity, and contrast sensitivity. Training resulted in a complete reversal of binocular reading inhibition in 30% of patients.

CONCLUSIONS

For patients with binocular inhibition due to central vision loss, BF training to stabilize fixation and to bring the monocular PRLs into correspondence on functioning retina in both eyes is an efficient rehabilitation method to improve binocular performance.

Approaching rehabilitation in patients with advanced glaucoma

Vision loss from advanced glaucoma is currently irreversible and impairs functional visual ability to effectively perform everyday tasks in a number of distinct functional domains. Vision rehabilitation strategies have been demonstrated to be effective in low vision populations and should be utilized in persons with advanced glaucoma to reduce disability and improve quality of life. Initial challenges to rehabilitation include an incomplete understanding of vision rehabilitation by the physician and patient, motivation to integrate rehabilitation into the plan of care, and availability of suitable providers to deliver this care. Physicians, working with well-trained vision rehabilitation providers can maximize function in important visual domains customized to the patient based on their needs, specific complaints, severity/pattern of visual damage, and comorbidities. Potential rehabilitative strategies to be considered for reading impairment include spectacle correction, visual assistive equipment, and sensory substitution, while potential strategies to facilitate driving in those deemed safe to do so include refractive correction, lens design, building confidence, restriction of driving to safer conditions, and avoiding situations where cognitive load is high. Mobility is frequently disrupted in advanced glaucoma, and can be addressed through careful distance refraction, behavior modification, home modification, mobility aids, walking assistance (i.e., sighted guide techniques), and smartphone/wearable technologies. Visual motor complaints are best addressed through optimization of lighting/contrast, sensory substitution, IADL training, and education. Special rehabilitative concerns may arise in children, where plans must be coordinated with schools, and working adults, where patients should be aware of their rights to accommodations to facilitate specific job tasks.

Binocular Summation of Visual Acuity at High and Low Contrast in Early Glaucoma

PRCIS

This study examined the integrity of binocular summation function in patients with mild glaucoma. We found that binocular summation of visual acuity is preserved in these patients, despite their reduced monocular inputs.

PURPOSE

Binocular summation represents superiority of binocular to monocular performance. In this study we examined the integrity of binocular summation function in patients with early glaucoma who had structural glaucomatous changes but otherwise had no significant interocular acuity asymmetry or other functional deficit detected with standard clinical measures.

MATERIALS AND METHODS

Participants included 48 patients with early glaucoma according to Hodapp, Anderson, and Parrish 2 (HAP2) criteria (age 65±12 y) and 42 healthy controls (age 60±12 y), matched for stereoacuity. Visual acuity was assessed binocularly and monocularly at high (95%) and low (25%) contrast using the Early Treatment Diabetic Retinopathy Study (ETDRS) charts at 6 m. Binocular acuity summation was evaluated utilizing a binocular ratio (BR).

RESULTS

Overall, binocular and monocular visual acuity of the control group was better than that of the glaucoma group for both contrast levels, P =0.001. For the glaucoma group, there was a significant difference between BRs at high and low contrast, 0.01±0.05 and 0.04±0.06 ( P =0.003), respectively. For the control group, the difference between BR at high and low contrast was not statistically significant, 0.00±0.07 and 0.02±0.06 ( P =0.25), respectively.

CONCLUSION

For patients with early glaucoma, binocular summation function for visual acuity was preserved at both contrast levels. This suggests an adaptation of the visual system in early stages of glaucoma that allows for normal binocular summation in the presence of reduced monocular visual input.

Binocular visual function and fixational control in patients with macular disease: A review

For normally sighted observers, the centre of the macula—the fovea—provides the sharpest vision and serves as the reference point for the oculomotor system. Typically, healthy observers have precise oculomotor control and binocular visual performance that is superior to monocular performance. These functions are disturbed in patients with macular disease who lose foveal vision. An adaptation to central vision loss is the development of a preferred retinal locus (PRL) in the functional eccentric retina, which is determined with a fixation task during monocular viewing. Macular disease often affects the two eyes unequally, but its impact on binocular function and fixational control is poorly understood. Given that patients’ natural viewing condition is binocular, the aim of this article was to review current research on binocular visual function and fixational oculomotor control in macular disease. Our findings reveal that there is no overall binocular gain across a range of visual functions, although clear evidence exists for subgroups of patients who exhibit binocular summation or binocular inhibition, depending on the clinical characteristics of their two eyes. The monocular PRL of the better eye has different characteristics from that of the worse eye, but during binocular viewing the PRL of the better eye drives fixational control and may serve as the new reference position for the oculomotor system. We conclude that evaluating binocular function in patients with macular disease reveals important clinical aspects that otherwise cannot be determined solely from examining monocular functions, and can lead to better disease management and interventions.

Eye Movements in Macular Degeneration

In healthy vision, the fovea provides high acuity and serves as the locus for fixation achieved through saccadic eye movements. Bilateral loss of the foveal regions in both eyes causes individuals to adopt an eccentric locus for fixation. This review deals with the eye movement consequences of the loss of the foveal oculomotor reference and the ability of individuals to use an eccentric fixation locus as the new oculomotor reference. Eye movements are an integral part of everyday activities, such as reading, searching for an item of interest, eye-hand coordination, navigation, or tracking an approaching car. We consider how these tasks are impacted by the need to use an eccentric locus for fixation and as a reference for eye movements, specifically saccadic and smooth pursuit eye movements. Expected final online publication date for the Annual Review of Vision Science, Volume 7 is September 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Contrast Sensitivity on 1/f Noise Is More Greatly Impacted by Older Age for the Fovea Than Parafovea

SIGNIFICANCE

Contrast sensitivity changes across the visual field with age and is often measured clinically with various forms of perimetry on plain backgrounds. In daily life, the visual scene is more complicated, and therefore, the standard clinical measures of contrast sensitivity may not predict a patient's visual experience in more natural environments.

PURPOSE

This study aims to determine whether contrast thresholds in older adults are different from younger adults when measured on a 1/f noise background (a nonuniform background whose spatial frequency content is similar to those present in the natural vision environments).

METHODS

Twenty younger (age range, 20 to 35 years) and 20 older adults (age range, 61 to 79 years) with normal ocular health were recruited. Contrast thresholds were measured for a Gabor patch of 6 cycles per degree (sine wave grating masked by a Gaussian envelope of standard deviation 0.17°) presented on 1/f noise background (root-mean-square contrast, 0.05 and 0.20) that subtended 15° diameter of the central visual field. The stimulus was presented at four eccentricities (0°, 2°, 4°, and 6°) along the 45° meridian in the noise background, and nine contrast levels were tested at each eccentricity. The proportion of correct responses for detecting the target at each eccentricity was obtained, and psychometric functions were fit to estimate the contrast threshold.

RESULTS

Older adults demonstrate increased contrast thresholds compared with younger adults. There was an eccentricity-dependent interaction with age, with the difference between groups being highest in the fovea compared with other eccentricities. Performance was similar for the two noise backgrounds tested.

CONCLUSIONS

Our results revealed a strong eccentricity dependence in performance between older and younger adults, highlighting age-related differences in the contrast detection mechanisms between fovea and parafovea for stimuli presented on nonuniform backgrounds.

Topical Review: Assessment of Binocular Sensory Processes in Low Vision

SIGNIFICANCE

This article summarizes the evidence for a higher prevalence of binocular vision dysfunctions in individuals with vision impairment. Assessment for and identification of binocular vision dysfunctions can detect individuals experiencing difficulties in activities including reading, object placement tasks, and mobility.Comprehensive vision assessment in low vision populations is necessary to identify the extent of remaining vision and to enable directed rehabilitation efforts. In patients with vision impairment, little attention is typically paid to assessments of binocular vision, including ocular vergence, stereopsis, and binocular summation characteristics. In addition, binocular measurements of threshold automated visual fields are not routinely performed in clinical practice, leading to an incomplete understanding of individuals' binocular visual field and may affect rehabilitation outcomes.First, this review summarizes the prevalence of dysfunctions in ocular vergence, stereopsis, and binocular summation characteristics across a variety of ocular pathologies causing vision impairment. Second, this review examines the links between clinical measurements of binocular visual functions and outcome measures including quality of life and performance in functional tasks. There is an increased prevalence of dysfunctions in ocular alignment, stereopsis, and binocular summation across low vision cohorts compared with those with normal vision. The identification of binocular vision dysfunctions during routine low vision assessments is especially important in patients experiencing difficulties in activities of daily living, including but not limited to reading, object placement tasks, and mobility. However, further research is required to determine whether addressing the identified deficits in binocular vision in low vision rehabilitative efforts directly impacts patient outcomes.

Reading with central vision loss: binocular summation and inhibition

Purpose

There are conflicting reports as to whether there is a binocular advantage or disadvantage when reading with central vision loss. This study examined binocular reading summation in patients with macular degeneration.

Methods

Seventy‐one patients with bilateral central vision loss [mean age: 63 (S.D. = 21) years] participated. Reading performances during binocular and monocular viewing with the better eye (i.e., the eye with the best monocular visual acuity) were evaluated using different versions of the Italian MNREAD reading chart (www.precision‐vision.com). Fixation stability and preferred retinal loci (PRLs) were recorded monocularly for each eye. The overall sample was split into inhibition, equality, and summation groups based on the binocular ratio (i.e., binocular/monocular) of the maximum reading speed.

Results

41% of patients experienced binocular inhibition, 42% summation, and 17% equality. Binocular reading speed of the inhibition group was approximately 30 words per minute slower than those of the equality and summation groups, although the inhibition group had the best visual acuity. These patients generally had monocular PRLs in non‐corresponding locations temporal or nasal to the scotoma, had the largest interocular acuity difference and lacked residual stereopsis. The three groups did not differ in fixational control, contrast sensitivity or critical print size.

Conclusions

Equal proportions of patients with central vision loss show binocular reading summation and inhibition. Patients with binocular reading inhibition have poorer reading performance and different clinical characteristics than those with binocular reading summation and equality.

Perceptual learning in patients with Stargardt disease

OBJECTIVE

To evaluate the efficacy of Perceptual Learning in improving the peripheral reading performance of patients with Stargardt disease (STGD).

DESIGN

Prospective observational randomized study.

PARTICIPANTS

Fourteen consecutive patients (7 females, 7 males; median age of 50.4 ± 12.8 years) with STGD were analyzed and divided into two groups: Group A received "Win-flash" as Perceptual Learning training and Group B was used as control.

METHODS

Subjects underwent an ophthalmic evaluation at baseline, after perceptual learning training and at 6 months of follow-up. Outcomes measured included reading speed, contrast sensitivity and fixation stability.

RESULTS

Reading speed improved of 51,7% after training in group A. Visual acuity, contrast sensitivity and fixation stability enhanced in group A after training from 0.89 (±0.09) LogMAR to 0.75 (±0.2) LogMAR (t(6)= 3.6, p= 0.001), from 0.8 (±0.3) LogC (0.6 - 0.9) to 1.3 (±0.3) LogC (t(13)=3.17, p= 0.003) and from 59.3 % (± 24.3) to 71.5 % (± 20.4) (t(13)=1.8 p= 0.04), respectively. No changes were found in group B. At 6-monts of follow-up, visual acuity and contrast sensitivity decreased in group A.

CONCLUSIONS

STGD patients receiving "Win-flash training", as PL technique, showed an improvement of reading performance on a real-world task. Early follow-up for perceptual learning re-intervention should be considered.

Lighting Needs and Lighting Comfort during Reading with Age-Related Macular Degeneration

This study investigated the effects of changes in luminance on the oral reading speeds of 13 participants with age-related macular degeneration (AMD) and a control group of six age-matched persons with typical vision. For the AMD participants, self-reports of light preferences were also recorded. In the AMD group, reading rates depended on light levels and were considerably lower than those of the control group. Reading speeds differed substantially among the AMD participants and, to obtain a functional range of luminance levels for reading, a combination of objective measurements and self-reports were required.

A Novel Vision-Enhancing Technology for Low-Vision Impairments

Ocular disorders such as vitreoretinal pathologies are widespread, especially in older adults. In particular, degenerative diseases of the retina such as macular senile degenerations are on the rise and affect millions of people with hundreds of thousands of new cases each year. These diseases can cause profoundly disabling visual impairments, in some cases severely compromising the central and/or the peripheral vision in one or both eyes. In this paper, we present a novel vision aids technology that allows for correcting or attenuating the perception of visual field defects due to ocular pathologies of diverse origins or traumas by using techniques of 3D visualisation, eye tracking, and image processing. The presented technology is mainly conceived for providing vision aids that can significantly improve the quality of life of people with this kind of visual disorders. As well, it could be employed for supporting the diagnosis of ocular dysfunctions and for monitoring the progression of diseases. The technology shown in this work is protected by an International Application in Patent Cooperation Treaty (PCT).

Binocular summation revisited: Beyond √2

Our ability to detect faint images is better with two eyes than with one, but how great is this improvement? A meta-analysis of 65 studies published across more than 5 decades shows definitively that psychophysical binocular summation (the ratio of binocular to monocular contrast sensitivity) is significantly greater than the canonical value of √2. Several methodological factors were also found to affect summation estimates. Binocular summation was significantly affected by both the spatial and temporal frequency of the stimulus, and stimulus speed (the ratio of temporal to spatial frequency) systematically predicts summation levels, with slow speeds (high spatial and low temporal frequencies) producing the strongest summation. We furthermore show that empirical summation estimates are affected by the ratio of monocular sensitivities, which varies across individuals, and is abnormal in visual disorders such as amblyopia. A simple modeling framework is presented to interpret the results of summation experiments. In combination with the empirical results, this model suggests that there is no single value for binocular summation, but instead that summation ratios depend on methodological factors that influence the strength of a nonlinearity occurring early in the visual pathway, before binocular combination of signals. Best practice methodological guidelines are proposed for obtaining accurate estimates of neural summation in future studies, including those involving patient groups with impaired binocular vision. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

Changes in Fixation Stability with Time during Binocular and Monocular Viewing in Maculopathy

The purpose of this study was to examine changes in fixation stability over time during binocular and monocular viewing in patients with age-related macular degeneration (AMD). Seventeen patients with AMD and 17 controls were enrolled. Using an EyeLink eyetracker (SR Research Ltd., Mississauga, Ontario, Canada), fixation stability was recorded binocularly and monocularly with each eye for a duration of 15 s while the fellow eye was covered. Fixation stability was analyzed over 3 s intervals for each condition using a 68% bivariate contour ellipse area. Fixation stability did not change with time during binocular viewing for both groups, both monocular conditions for the control group, and monocular viewing with the better eye for the AMD group. However, during monocular viewing with the worse eye, the test of within-subject contrasts showed linear improvement in fixation stability with time (p = 0.016). In conclusion, in patients with AMD, monocular fixational control with the worse eye is poor, but improves with time.

Binocular contrast summation and inhibition depends on spatial frequency, eccentricity and binocular disparity

PURPOSE

When central vision is compromised, visually-guided behaviour becomes dependent on peripheral retina, often at a preferred retinal locus (PRL). Previous studies have examined adaptation to central vision loss with monocular 2D paradigms, whereas in real tasks, patients make binocular eye movements to targets of various sizes and depth in 3D environments.

METHODS

We therefore examined monocular and binocular contrast sensitivity functions with a 26-AFC (alternate forced choice) band-pass filtered letter identification task at 2° or 6° eccentricity in observers with simulated central vision loss. Binocular stimuli were presented in corresponding or non-corresponding stereoscopic retinal locations. Gaze-contingent scotomas (0.5° radius disks of pink noise) were simulated independently in each eye with a 1000 Hz eye tracker and 120 Hz dichoptic shutter glasses.

RESULTS

Contrast sensitivity was higher for binocular than monocular conditions, but only exceeded probability summation at low-mid spatial frequencies in corresponding retinal locations. At high spatial frequencies or non-corresponding retinal locations, binocular contrast sensitivity showed evidence of interocular suppression.

CONCLUSIONS

These results suggest that binocular vision deficits may be underestimated by monocular vision tests and identify a method that can be used to select a PRL based on binocular contrast summation.

Fixation parameter test-retest repeatability of the worse eye in central field loss

OBJECTIVE

Patients with bilateral central field loss develop peripheral retinal loci (PRLs) in the functional eccentric retina. PRL characteristics and visual performance in the better-seeing eye (BE) of these patients have previously been reported. In this study, we determined the test-retest repeatability of fixation parameters, including fixation stability, PRL eccentricity, and PRL span in the worse-seeing eye (WE).

DESIGN

Retrospective consecutive case series.

PARTICIPANTS

Thirty-six patients with bilateral central field loss referred from the Toronto Western Hospital Retina Clinic, who had completed 2 consecutive fixation examinations on the same day.

METHODS

Fixation stability was recorded using the Nidek MP-1 microperimeter (Nidek Technologies Srl., Padova, Italy). For each fixation recording, the following parameters were retrieved: (i) 68.2% bivariate contour ellipse area (BCEA), (ii) PRL span (major and minor axes of the BCEA), (iii) PRL meridian (polar angle), and (iv) PRL eccentricity. Test-retest repeatability for each parameter was assessed using Bland-Altman plots to determine 95% limits of agreement.

RESULTS

The mean difference between the fixation trial pairs and the 95% limits of agreement for fixation stability, PRL major axis, PRL minor axis, PRL meridian, and PRL eccentricity were 0.06 ± 0.47 log deg², 0.05° ± 1.42°, 0.07° ± 0.63°, -0.44° ± 66.0°, and -0.23° ±1.56°, respectively.

CONCLUSIONS

The fixation parameters in the WE showed robust repeatability, comparable to that of the BE as determined from previous studies. The WE's fixation repeatability should be considered in the interpretation of fixation outcome measures subsequent to treatment interventions.

Visual processing in patients with age-related macular degeneration performing a face detection test

PURPOSE

People with age-related macular degeneration (AMD) have difficulties in familiar face recognition and facial expression discrimination. Our aim was to evaluate the visual processing of faces in AMD patients and whether this would be improved by anti-vascular endothelial growth factor therapy. This was a prospective interventional cohort study.

PATIENTS

Twelve patients with monocular wet AMD and 6 control subjects were recruited. Face detection processes were studied using cortical event-related potentials (ERPs). Patients received 3 bevacizumab intravitreal injections to the single affected eye. At baseline and 4-6 weeks after the last injection, clinical presentation and ERPs of the face task were evaluated. Face pictures were shown as targets (16.7%) among standard pictures of pixelated faces in an oddball-type paradigm.

RESULTS

Face pictures elicited well-defined electrical components in occipital and parieto-occipital cortical areas at baseline and after treatment. The face-specific N170 component was evident in all subjects with longer peak latency in patients than in controls (170±13 vs 155±14, P=0.032). Unexpectedly, an early component reflecting unintentional prediction of perceiving a face, that is, deviance-related negativity, was present in patients and controls. Visual acuity of the affected eye seemed improved in patients from logarithm of the minimum angle of resolution 0.71 (±0.33) to 0.52 (±0.39) by 119 (±23) days without accompanying significant change in face-specific ERPs.

CONCLUSIONS

Monocular wet AMD distinctly influenced face-specific brain electrophysiological components. However, the anti-vascular endothelial growth factor treatment did not improve the binocular face detection ability. The EudraCT number of this study is 2012-000765-20.

Depth Perception and Grasp in Central Field Loss

Purpose

We set out to determine whether individuals with central field loss benefit from using two eyes to perform a grasping task. Specifically, we tested the hypothesis that this advantage is correlated with coarse stereopsis, in addition to binocular summation indices of visual acuity, contrast sensitivity, and binocular visual field.

Methods

Sixteen participants with macular degeneration and nine age-matched controls placed pegs on a pegboard, while their eye and hand movements were recorded. Importantly, the pegboard was placed near eye height, to minimize the contribution of monocular cues to peg position. All participants performed this task binocularly and monocularly. Before the experiment, we performed microperimetry to determine the profile of field loss in each eye and the locations of eccentric fixation (if applicable). In addition, we measured both acuity and contrast sensitivity monocularly and binocularly, and stereopsis by using both a RanDot test and a custom stereo test.

Results

Peg-placement time was significantly shorter and participants made significantly fewer errors with binocular than with monocular viewing in both the patient and control groups. Among participants with measurable stereopsis, binocular advantage in peg-placement time was significantly correlated with stereoacuity (ρ = −0.78; P = 0.003). In patients without measurable stereopsis, the binocular advantage was related significantly to the overlap in the scotoma between the two eyes (ρ = −0.81; P = 0.032).

Conclusions

The high correlation between grasp performance and stereoacuity indicates that coarse stereopsis may benefit tasks of daily living for individuals with central field loss.

Home lighting assessment for clients with low vision

OBJECTIVE

The goal was to develop an objective, comprehensive, near-task home lighting assessment for older adults with low vision.

METHOD

A home lighting assessment was developed and tested with older adults with low vision. Interrater and test-retest reliability studies were conducted. Clinical utility was assessed by occupational therapists with expertise in low vision rehabilitation.

RESULTS

Interrater reliability was high (intraclass correlation coefficient [ICC] = .83-1.0). Test-retest reliability was moderate (ICC = .67). Responses to a Clinical Utility Feedback Form developed for this study indicated that the Home Environment Lighting Assessment (HELA) has strong clinical utility.

CONCLUSION

The HELA provides a structured tool to describe the quantitative and qualitative aspects of home lighting environments where near tasks are performed and can be used to plan lighting interventions. The HELA has the potential to affect assessment and intervention practices of rehabilitation professionals in the area of low vision and improve near-task performance of people with low vision.

Reading training with threshold stimuli in people with central vision loss: a feasibility study

PURPOSE

To evaluate the effectiveness of a perceptual learning technique for improving reading performance of patients with central vision loss and to explore whether this learning generalizes to other visual functions.

METHODS

Ten patients with central vision loss were trained binocularly, in four consecutive sessions, with serially presented words printed at each patient's reading acuity limit. Patients read 10 blocks of 100 words in each session. They were encouraged to read the whole word and were discouraged to read letter by letter. Assessment sessions before and after training measured fixation stability, monocular and binocular visual acuity, as well as reading acuity, critical print size, and maximum reading speed with continuous text. Another six patients with central vision loss were included in a test-retest control group and were tested twice, 1 week apart, with no intervention.

RESULTS

The average time required to read a block of trials decreased significantly with each training session. After training, continuous text reading improved in terms of reading acuity (p = 0.017) and maximum reading speed (p = 0.01), but critical print size did not change. Binocular acuity improved significantly from an average of 0.54 logMAR before training to 0.44 logMAR after training. Binocular ratio (better eye acuity/binocular acuity) increased from an average of 1.0 before training to 1.17 after training. There was a 62% improvement in fixation stability in the better eye and 58% in the worse eye. There were no changes in the outcome measures for the test-retest control group.

CONCLUSIONS

The technique described in this article can be used for vision rehabilitation of patients with central vision loss. When training is done with size threshold stimuli, learning generalizes to visual acuity, continuous text reading, and fixation stability.

Residual stereopsis in age-related macular degeneration patients and its impact on vision-related abilities: a pilot study

OBJECTIVE

To determine the effect of residual stereopsis on vision-related abilities of low vision (LV) patients with age-related macular degeneration (AMD).

METHODS

Prospective non-randomized observational case series. Inclusion criteria included documented AMD, LV with best corrected visual acuity (BCVA) of 20/50-20/400 in the better eye, and ages between 50 and 90 years. Stereoacuity was measured using the near Frisby Stereotest. Vision related abilities were documented with the VA LV VFQ-48 questionnaire.

RESULTS

Twenty-seven subjects with mean age of 84±6 years old were recruited, of which 59.3% (16/27) were female. 59.3% (16/27) of the subjects were not able to see any stereoacuity plate, 25.9% (7/27) had stereoacuity of 340s of arc (SOA), 11.1% (3/27) had stereoacuity of 170 SOA and 3.7% (1/27) had stereoacuity of 85 SOA. The mean Overall Functional Visual Abilities (OFVA) score was significantly higher in those with stereopsis (2.25±0.99) than those without stereopsis (1.50±0.92) (P=0.028).

CONCLUSIONS

LV patients with stereopsis have better OFVA than those without. Stereopsis should be considered as a component of LV rehabilitation and considered as an outcome measure in research and clinical practice.

The worse eye is not as bad as it seems to be in AMD cases

OBJECTIVE

It is the aim of this study to review residual vision in the less used eye of patients with age-related macular degeneration (AMD) using modern concepts for residual visual functions in addition to traditional methods for assessing visual acuity.

DESIGN

The study was designed as a retrospective, nonrandomized, observational case series.

PARTICIPANTS

Consecutive cases tested with microperimetry instruments were identified from archives. Included were cases with diagnosed AMD of all age groups and all visual acuity levels.

METHODS

In all cases, microperimetric technology was used to assess residual visual function. Outcome measures selected for analysis were visual acuity, preferred retinal loci (PRL) topography, fixation stability, and PRL span.

RESULTS

Data were collected and analyzed for both eyes from 51 patients with AMD low vision. There were 23 males and 28 females whose mean age was 84 (± 7) years. Within the group the difference in visual acuity estimates between the better seeing and the less used eye was statistically significant (p = 0.001). Similar positive statistical significant differences were noticed at all spatial frequencies (except at 6 cycles/degree) when testing contrast sensitivity. All other measurements were not statistically different between the better seeing and the poorer eye. This applies to the fixation stability and PRL span estimates. Almost half (49%) of the cases showed retinal noncorrespondence of PRLs between the 2 eyes.

CONCLUSIONS

Visual acuity estimates are not a reliable measure for residual vision. The less used eye in AMD cases has much better residual vision than thought before according to modern outcome measures. This new concept should be taken into account by all practitioners and be applied during all low vision rehabilitation interventions.

Text accessibility by people with reduced contrast sensitivity

PURPOSE

Contrast sensitivity is reduced in people with eye disease, and also in older adults without eye disease. In this article, we compare contrast of text presented in print and digital formats with contrast sensitivity values for a large cohort of subjects in a population-based study of older adults (the Salisbury Eye Evaluation).

METHODS

Contrast sensitivity values were recorded for 2520 adults aged 65 to 84 years living in Salisbury, Maryland. The proportion of the sample likely to be unable to read text of different formats (electronic books, newsprint, paperback books, laser print, and LED computer monitors) was calculated using published contrast reserve levels required to perform spot reading, to read with fluency, high fluency, and under optimal conditions.

RESULTS

One percent of this sample had contrast sensitivity less than that required to read newsprint fluently. Text presented on an LED computer monitor had the highest contrast. Ninety-eight percent of the sample had contrast sensitivity sufficient for high fluent reading of text (at least 160 words/min) on a monitor. However, 29.6% were still unlikely to be able to read this text with optimal fluency.

CONCLUSIONS

Reduced contrast of print limits text accessibility for many people in the developed world. Presenting text in a high-contrast format, such as black laser print on a white page, would increase the number of people able to access such information. Additionally, making text available in a format that can be presented on an LED computer monitor will increase access to written documents.

Monocular vs. binocular measurement of spatial vision in elders

PURPOSE

To evaluate the frequency and magnitude of binocular gain (and loss) for high-contrast acuity, various low-contrast spatial vision measures and contrast sensitivity in an elderly population.

METHODS

Ninety-five individuals over the age of 70 (mean age 80.5 years, range, 71.8 to 93.5) with acuity of 20/40 (logMAR 0.3) or better in at least one eye participated. Each individual was tested binocularly and then monocularly on high-contrast acuity, various low-contrast acuity measures, and contrast sensitivity. Binocular gain for acuity measures was defined as better performance by one line or more under binocular conditions than with the better eye alone. Binocular loss was defined as poorer performance by one line or more binocularly than with the better eye alone. For contrast sensitivity, the criterion for binocular gain or loss was one letter triplet (0.15 log unit) or more difference. For each measure, the frequency of binocular gain and loss, as well as the mean gain or loss were determined.

RESULTS

The mean difference between binocular and better eye monocular acuity was <2 letters for all measures, suggesting little gain or loss. However, the percent of individuals showing a line or more of gain or loss ranged from approximately 20% for high-contrast acuity to 49.5% for low-contrast acuity at low luminance. This indicates that for 1/5 to (1/2) of individuals, binocular vision is not well represented by monocular vision measures. All low contrast measures and contrast sensitivity show more binocular gain/loss than standard acuity. As has been previously reported, in the presence of large interocular differences, binocular gain is not seen, but binocular loss does not necessarily occur.

CONCLUSIONS

For a significant portion of this elderly population, binocular performance is not well represented by better eye monocular measures. This indicates that to get a true sense of an individual';s vision function in daily life, one must measure vision binocularly.

Using contrast sensitivity to estimate the cost-effectiveness of verteporfin in patients with predominantly classic age-related macular degeneration

AIMS

To re-evaluate the cost-effectiveness of photodynamic therapy with verteporfin (Visudyne, Novartis AG, Switzerland) in patients with predominantly classic and classic choroidal neovascularization (CNV) owing to age-related macular degeneration (AMD), using new evidence on the impact of contrast sensitivity on health status.

METHOD

A health economic model is used to synthesise the evidence on contrast sensitivity and treatment rates from the TAP Investigation with health state utilities and costs. Impairment of visual function is estimated using a Markov model to predict transitions between states of contrast sensitivity. Each state is associated with costs and a health state utility. Total expected costs and benefits for a cohort of patients over a defined number of cycles are calculated. The expected health state utility for each disease state was estimated using results from a study of 209 patients with AMD in Sheffield. The model includes the costs associated with treatment and monitoring in the verteporfin treatment arm and costs offset by delaying the deterioration of visual function.

RESULTS

Beyond 3 years, the annual costs of the verteporfin arm are estimated to be less than the annual costs of the control arm, owing to the cost associated with higher blindness prevalence in the control arm. Over time, the results show that both the incremental utility and cost decreases. By 10 years, the estimated incremental cost-effectiveness is approximately pound20 996 per Quality-Adjusted Life Years.

CONCLUSION

The results of this study suggest that the verteporfin therapy in the treatment for patients with predominantly classic and classic CNV owing to AMD is encouraging.

Reading With Central Scotomas: Is There a Binocular Gain?

PURPOSE

The purpose of this study was to compare reading performance under binocular versus monocular viewing conditions in patients with bilateral age-related macular degeneration (AMD).

METHODS

Twenty-two patients with AMD participated. Distance acuity, reading acuity, and contrast sensitivity were recorded binocularly and monocularly with the better eye. An infrared eye tracker recorded eye movements during reading. Reading speed and reading eye movement parameters, including number of fixations and regressions, fixation duration, and number of saccades to find the next line, were calculated for both viewing conditions. The difference between binocular and monocular performance (binocular gain) was computed. Regression analysis was used to determine whether intraocular differences in distance and reading acuity and contrast sensitivity were predictive of binocular gain.

RESULTS

Reading speed when using both eyes was highly correlated with the reading speed for the better eye. There was a small, but not significant, advantage of binocular viewing (6.9 words/minute, p = 0.33). No significant difference was detected in any eye movement parameters when comparing both eyes with the better eye. Although some patients showed either positive or negative binocular gain, the amount of gain was not predicted by intraocular differences in acuity or contrast sensitivity.

CONCLUSIONS

Overall, there was no significant difference between binocular and monocular reading performance in patients with AMD.

Principles of modern low vision rehabilitation

Low vision rehabilitation is a new emerging subspecialty drawing from the traditional fields of ophthalmology, optometry, occupational therapy, and sociology, with an ever-increasing impact on our customary concepts of research, education, and services for the visually impaired patient. A multidisciplinary approach and coordinated effort are necessary to take advantage of new scientific advances and achieve optimal results for the patient. Accordingly, the intent of this paper is to outline the principles and details of a modern low vision rehabilitation service. All rehabilitation attempts must start with a first hand interview (the intake) for assessing functionality and priority tasks for rehabilitation, as well as assessing the patient's all-important cognitive skills. The assessment of residual visual functions follows the intake and offers a unique opportunity to measure, evaluate, and document accurately the extent of functional loss sustained by the patient from disease. An accurate assessment of residual visual functions includes assessment of visual acuity, contrast sensitivity, binocularity, refractive errors, perimetry, oculomotor functions, cortical visual integration, and light characteristics affecting visual functions. Functional vision assessment in low vision rehabilitation measures how well one uses residual visual functions to perform routine tasks, using different items under various conditions, throughout the day. Of the many functional vision skills known, reading skills is an obligatory item for all low vision rehabilitation assessments. Results of assessment guide rehabilitation professionals in developing rehabilitation plans for the individual and recommending appropriate low vision devices. The outcome from assessing residual visual functions is detection of visual functions that can be improved with the use of optical devices. Methods for prescribing devices such as image relocation with prisms to a preferred retinal locus, field displacement to primary gaze position, field expansion, and manipulation of light are practiced today in addition to, or instead of, magnification. Correction of refractive errors, occlusion therapy, enhancement of oculomotor skills, and field restitution are additional methods now available for prescribing devices leading to rehabilitation of visual functions. The outcome from assessing residual functional vision is detection of functional vision that can be improved with the use of vision therapy training. After restoration of optimal residual visual functions is achieved with optical devices, one can follow with training programs for restoration of lost vision-related skills. If an optical dispensary is available where prescribing of low vision devices routinely take place, this will help ensure familiarity and specialization of the dispensary and staff with low vision devices and their special dispensing requirements. The dispensing of low vision devices is an opportunity to introduce the device to the patient, train the patient in the correct use of the device for the task selected, and create a direct and continuous connection with the patient until the next encounter. Following assessment, prescribing, and dispensing of devices, a low vision practitioner, ophthalmologist or optometrist, is responsible for recommending and prescribing vision therapy training to improve residual functional vision. An attempt to present a template for a comprehensive modern low vision rehabilitation practice is made here by summarizing scientific developments in the field and stressing the multidisciplinary involvement required for this kind of practice. It is hoped that this paper and other initiatives from colleagues, the public, and government will promote and raise awareness of modern low vision rehabilitation for the benefit of all.

Binocular interactions in patients with age-related macular degeneration: Acuity summation and rivalry

This study examined two aspects of binocular function in patients with age-related macular degeneration (AMD): summation/inhibition of visual acuity and rivalry. The performance of 17 patients with AMD was compared with that of 17 elderly controls and 21 young people. Monocular and binocular acuities were measured using a multiple-E optotype test. Binocular ratios, defined as the better-eye acuity divided by the binocular acuity, were calculated. We also measured eye dominance during rivalry (proportion of time the participants reported perceiving the input to each eye) and rivalry rates (number of alternations per minute). The results showed that while overall binocular ratios were similar for the three groups, the frequency distributions of people who experienced inhibition, equality or summation were different for the young and AMD groups. In the rivalry test, patients experienced more piecemeal perception than the elderly and young controls, but time dominance from the better-seeing eye was comparable for the three groups. Rivalry rates decreased with age and further with pathology. Moreover, rivalry time dominance of the worse-seeing eye was negatively correlated with interocular acuity differences for the AMD group.

Visual function and dysfunction in early and late age-related maculopathy

Late age-related maculopathy (ARM) is responsible for the majority of blind registrations in the Western world among persons over 50 years of age. It has devastating effects on quality of life and independence and is becoming a major public health concern. Current treatment options are limited and most aim to slow progression rather than restore vision; therefore, early detection to identify those patients most suitable for these interventions is essential. In this work, we review the literature encompassing the investigation of visual function in ARM in order to highlight those visual function parameters which are affected very early in the disease process. We pay particular attention to measures of acuity, contrast sensitivity (CS), cone function, electrophysiology, visual adaptation, central visual field sensitivity and metamorphopsia. We also consider the impact of bilateral late ARM on visual function as well as the relationship between measures of vision function and self-reported visual functioning. Much interest has centred on the identification of functional changes which may predict progression to neovascular disease; therefore, we outline the longitudinal studies, which to date have reported dark-adaptation time, short-wavelength cone sensitivity, colour-match area effect, dark-adapted foveal sensitivity, foveal flicker sensitivity, slow recovery from glare and slower foveal electroretinogram implicit time as functional risk factors for the development of neovascular disease. Despite progress in this area, we emphasise the need for longitudinal studies designed in light of developments in disease classification and retinal imaging, which would ensure the correct classification of cases and controls, and provide increased understanding of the natural course and progression of the disease and further elucidate the structure-function relationships in this devastating disorder.

Binocular function in patients with age-related macular degeneration: a review

Normally sighted observers typically benefit from binocular viewing when monocular sensitivities are equivalent. Age-related macular degeneration (AMD) not only destroys the foveal vision, however, but it also affects the 2 eyes unequally, providing grounds for impairment of binocular function. The aim of the present article is to provide a review of the current research on the effect of AMD on binocular vision. The main findings to date reveal that a high proportion of patients show characteristics of binocular contrast inhibition at low and medium spatial frequencies. Yet binocular acuity gain is not different from that of age-matched control participants without AMD. Additional findings show that rivalry processes are severely disrupted in patients with AMD. The effects of the disease on other binocular functions have yet to be explored. Knowledge of binocular function in AMD may one day help clinicians decide on the most appropriate management and rehabilitation techniques.

Age-related macular degeneration: filter lenses help in certain situations

PURPOSE

To investigate the ability of different filter lenses to enhance the contrast sensitivity of patients with age-related macular degeneration (AMD).

METHODS

A total of 32 patients with non-exudative AMD and no other significant eye diseases underwent the study tests using their optimal correction. We used Hyvärinen's contrast sensitivity tests with 100%, 10%, 5%, 2.5% and 1.25% charts. All the tests were made without filter lenses and with the Corning 527 and LVI 527 lenses.

RESULTS

With the 100% charts, there was a slight tendency towards contrast sensitivity improvement with LVI filter lenses, but the degree of improvement was not statistically significant. With the 10% charts, contrast sensitivity improved significantly with LVI 527 filter lenses, but not with Corning 527 lenses. It was not possible to perform statistical analyses of the results with the 5%, 2.5% and 1.25% charts.

CONCLUSION

Use of LVI filter lenses may improve contrast sensitivity in certain situations in patients with AMD.