Perspective on Vision Science-Informed Interventions for Central Vision Loss

Abstract

Pathologies affecting central vision, and macular degeneration (MD) in particular, represent a growing health concern worldwide, and the leading cause of blindness in the Western World. To cope with the loss of central vision, MD patients often develop compensatory strategies, such as the adoption of a Preferred Retinal Locus (PRL), which they use as a substitute fovea. However, visual acuity and fixation stability in the visual periphery are poorer, leaving many MD patients struggling with tasks such as reading and recognizing faces. Current non-invasive rehabilitative interventions are usually of two types: oculomotor, aiming at training eye movements or teaching patients to use or develop a PRL, or perceptual, with the goal of improving visual abilities in the PRL. These training protocols are usually tested over a series of outcome assessments mainly measuring low-level visual abilities (visual acuity, contrast sensitivity) and reading. However, extant approaches lead to mixed success, and in general have exhibited large individual differences. Recent breakthroughs in vision science have shown that loss of central vision affects not only low-level visual abilities and oculomotor mechanisms, but also higher-level attentional and cognitive processes. We suggest that effective interventions for rehabilitation after central vision loss should then not only integrate low-level vision and oculomotor training, but also take into account higher level attentional and cognitive mechanisms.

Keywords: clinical intervention strategy perspective; macular degeneration; neural plasticity; oculomotor abilities; perceptual learning; visual rehabilitation.

FIGURE 1

(A) Typical representation of the visual field of a patient with central vision loss. In reality, patients with central vision loss are rarely aware of the location and extent of their scotoma, and, crucially, said scotoma does not present clear-cut borders as it is the case of the artificial scotoma, which is shown in panel (B). A typical compensatory strategy in patients with central vision loss is the development of a peripheral retinal locus, or PRL, an eccentric fixation region close to the border of the scotoma, that patients use to fixate and solve demanding visual tasks, i.e., face recognition. Panel (C) shows where the scotoma might be placed to allow the face in the image to fall outside the scotoma and on the PRL. Panel (D) shows placement of a simulated scotoma allowing the face to be visible. Note once more that the hard edges of the simulated scotoma are different from the true scotoma, and may contribute to speeded development of a PRL with this paradigm (Walsh and Liu, 2014).

FIGURE 2

Multidimensional approach to low vision rehabilitation in MD. Figure illustrates how each of visual perception, oculomotor control and cognitive control are interconnected dimensions of vision that contribute to effective vision.

FIGURE 3

Coordinated attentional training (CAT) display. The target, a Gabor patch tilted left or right, appears in a random location on screen, accompanied by a visual (left) and an acoustic (right) cue. The visual cue, a circle surrounding the target, is either bright (100% luminance) or dim (60% luminance). The auditory cue is a simple tone whose pitch is mapped to the y axis of the target (lower for the bottom of the screen, higher for the top) and whose left-right panning target (based upon inter-aural time/level differences) depends on the target location on the x axis.

FIGURE 4

Preliminary results from our perceptual learning study comparing a standard perceptual learning (SPL) with a coordinated attentional training (CAT). In the first two rows, left side shows data from MD participants (A,C for visual acuity and MNRread respectively), while right side shows data from healthy participants trained with gaze-contingent, simulated scotoma (B,D for visual acuity and MNRread respectively). The last row shows additional assessment tasks only collected in MD participants (motion direction discrimination and Trail Making Test, E,F respectively). In SPL training, the Gabor target was always presented in the center of the screen and accompanied by a neutral acoustic cue. In CAT the target could appear anywhere on screen, thus involving visual search and gaze re-orienting. The target presentation was accompanied by a visual cue (a white circle around the target) and an auditory cue whose pitch and interaural difference were matched to the target location on screen. In the Trail Making Test, participants are presented with a piece of paper with circles containing numbers in random order and asked to use a pencil to connect them in ascending order as quickly as possible. The dependent measure of this test is the completion time expressed in seconds.