Mapping the binocular scotoma in macular degeneration

Assessing REALTER simulator: analysis of ocular movements in simulated low-vision conditions with extended reality technology

Immersive technology, such as extended reality, holds promise as a tool for educating ophthalmologists about the effects of low vision and for enhancing visual rehabilitation protocols. However, immersive simulators have not been evaluated for their ability to induce changes in the oculomotor system, which is crucial for understanding the visual experiences of visually impaired individuals. This study aimed to assess the REALTER (Wearable Egocentric Altered Reality Simulator) system's capacity to induce specific alterations in healthy individuals' oculomotor systems under simulated low-vision conditions. We examined task performance, eye movements, and head movements in healthy participants across various simulated scenarios. Our findings suggest that REALTER can effectively elicit behaviors in healthy individuals resembling those observed in individuals with low vision. Participants with simulated binocular maculopathy demonstrated unstable fixations and a high frequency of wide saccades. Individuals with simulated homonymous hemianopsia showed a tendency to maintain a fixed head position while executing wide saccades to survey their surroundings. Simulation of tubular vision resulted in a significant reduction in saccade amplitudes. REALTER holds promise as both a training tool for ophthalmologists and a research instrument for studying low vision conditions. The simulator has the potential to enhance ophthalmologists' comprehension of the limitations imposed by visual disabilities, thereby facilitating the development of new rehabilitation protocols.

Visual Field Dependence Persists in Age-Related Central Visual Field Loss

Purpose

To examine whether the age-related increase in visual field dependence persists in older adults with central field loss (CFL).

Methods

Twenty individuals with CFL were grouped into participants with age-related binocular CFL (CFL, n = 9), age-related monocular CFL/relative scotomata (mCFL, n = 8), and CFL occurring at a young age (yCFL, n = 3). Seventeen controls were age-matched to the older CFL groups (OA) and three to the yCFL group (yOA). Participants judged the tilt direction of a rod presented at various orientations under conditions with and without a visual reference. Visual field dependence was determined as the difference in judgment bias between trials with and without the visual reference. Visual field dependence was examined between groups and relative to visual acuity and contrast sensitivity.

Results

All older groups performed similarly without the visual reference. The CFL group showed greater visual field dependence than the OA group (Mann-Whitney U test; U = 39, P = 0.045). However, there was no group difference when considering all three older groups (Kruskal-Wallis ANOVA; H(2, N = 34) = 4.31, P = 0.116). Poorer contrast sensitivity correlated with greater visual field dependence (P = 0.017; ρ = -0.43).

Conclusions

Visual field dependence persists in older adults with CFL and seems exacerbated in those with dense binocular scotomata. This could be attributed to the sensitivity of the spared peripheral retina to orientation and motion cues. The relationship with contrast sensitivity further suggests that a decline in visual function is associated with an increase in visual field dependence beyond the effects of normal aging. These observations can guide tailored care and rehabilitation in older adults with CFL.

A review of experimental task design in psychophysical eye tracking research

While eye tracking is a technique commonly used in the experimental study of higher-level perceptual processes such as visual search, working memory, reading, and scene exploration, its use for the quantification of basic visual functions (visual acuity, contrast sensitivity, color vision, motion detection) is less explored. The use of eye movement features as dependent variables in a psychophysical investigation can serve multiple roles. They can be central in studies with neurological patients or infants that cannot comply with verbal instructions, understand task demands, and/or emit manual responses. The technique may also serve a complementary role, determining the conditions under which a manual or verbal response is given, such as stimulus position in the visual field, or it can afford the analysis of new dependent variables, such as the time interval between oculomotor and manual responses. Our objective is to review the literature that applied the eye tracking technique to psychophysical problems. The two questions our review raises are: can eye movements (reflex or voluntary) be an objective index of stimulus detection in psychophysical tasks? If so, under what conditions, and how does it compare with traditional paradigms requiring manual responses? Our (non-systematic) methodological review selected studies that used video-oculography as the technique of choice and had a basic visual function as their primary object of investigation. Studies satisfying those criteria were then categorized into four broad classes reflecting their main research interest: (1) stimulus detection and threshold estimation, (2) the effects of stimulus properties on fixational eye movements, (3) the effects of eye movements on perception, and (4) visual field assessment. The reviewed studies support the idea that eye tracking is a valuable technique for the study of basic perceptual processes. We discuss methodological characteristics within each of the proposed classification area, with the objective of informing future task design.

A New Vessel-Based Method to Estimate Automatically the Position of the Nonfunctional Fovea on Altered Retinography From Maculopathies

Purpose

The purpose of this study was to validate a new automated method to locate the fovea on normal and pathological fundus images. Compared to the normative anatomic measures (NAMs), our vessel-based fovea localization (VBFL) approach relies on the retina's vessel structure to make predictions.

Methods

The spatial relationship between the fovea location and vessel characteristics is learnt from healthy fundus images and then used to predict fovea location in new images. We evaluate the VBFL method on three categories of fundus images: healthy images acquired with different head orientations and fixation locations, healthy images with simulated macular lesions, and pathological images from age-related macular degeneration (AMD).

Results

For healthy images taken with the head tilted to the side, the NAM estimation error is significantly multiplied by 4, whereas VBFL yields no significant increase, representing a 73% reduction in prediction error. With simulated lesions, VBFL performance decreases significantly as lesion size increases and remains better than NAM until lesion size reaches 200 degrees2. For pathological images, average prediction error was 2.8 degrees, with 64% of the images yielding an error of 2.5 degrees or less. VBFL was not robust for images showing darker regions and/or incomplete representation of the optic disk.

Conclusions

The vascular structure provides enough information to precisely locate the fovea in fundus images in a way that is robust to head tilt, eccentric fixation location, missing vessels, and actual macular lesions.

Translational Relevance

The VBFL method should allow researchers and clinicians to assess automatically the eccentricity of a newly developed area of fixation in fundus images with macular lesions.

Mapping residual stereopsis in macular degeneration

Individuals with macular degeneration typically lose vision in the central region of one or both eyes. A binocular scotoma occurs when vision loss occurs in overlapping locations in both eyes, but stereopsis is impacted even in the non-overlapping region wherever the visual field in either eye is affected. We used a novel stereoperimetry protocol to measure local stereopsis across the visual field (up to 25° eccentricity) to determine how locations with functional stereopsis relate to the scotomata in the two eyes. Participants included those with monocular or binocular scotomata and age-matched controls with healthy vision. Targets (with or without depth information) were presented on a random dot background. Depth targets had true binocular disparity of 20' (crossed), whereas non-depth targets were defined by monocular cues such as contrast and dot density. Participants reported target location and whether it was in depth or flat. Local depth sensitivity (d') estimates were then combined to generate a stereopsis map. This stereopsis map was compared to the union of the monocular microperimetry estimates that mapped out the functional extent of the scotoma in each eye. The "union" prediction aligned with residual stereopsis, showing impaired stereopsis within this region and residual stereopsis outside this region. Importantly, the stereoblind region was typically more extensive than the binocular scotoma defined by the intersection (overlap) of the scotomata. This explains why individuals may have intact binocular visual fields but be severely compromised in tasks of daily living that benefit from stereopsis, such as eye-hand coordination and navigation.

Impact of neovascular age-related macular degeneration on eye-movement control during scene viewing: Viewing biases and guidance by visual salience

Human vision requires us to analyze the visual periphery to decide where to fixate next. In the present study, we investigated this process in people with age-related macular degeneration (AMD). In particular, we examined viewing biases and the extent to which visual salience guides fixation selection during free-viewing of naturalistic scenes. We used an approach combining generalized linear mixed modeling (GLMM) with a-priori scene parcellation. This method allows one to investigate group differences in terms of scene coverage and observers' well-known tendency to look at the center of scene images. Moreover, it allows for testing whether image salience influences fixation probability above and beyond what can be accounted for by the central bias. Compared with age-matched normally sighted control subjects (and young subjects), AMD patients' viewing behavior was less exploratory, with a stronger central fixation bias. All three subject groups showed a salience effect on fixation selection-higher-salience scene patches were more likely to be fixated. Importantly, the salience effect for the AMD group was of similar size as the salience effect for the control group, suggesting that guidance by visual salience was still intact. The variances for by-subject random effects in the GLMM indicated substantial individual differences. A separate model exclusively considered the AMD data and included fixation stability as a covariate, with the results suggesting that reduced fixation stability was associated with a reduced impact of visual salience on fixation selection.

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.