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Macular degeneration (MD) is the main cause of vision impairment globally, and it is projected to affect 248 million people worldwide by 20401. Late-stage MD is characterized by damage to the photoreceptors in the center of the visual field (fovea). Loss of central vision has severe effects on daily tasks that rely on central vision, such as navigation2, reading3, and recognizing faces4. Consequences of MD greatly impact the quality of life of these individuals5 and lead to negative psychological consequences6. Patients with MD, deprived of their central vision, may spontaneously develop compensatory oculomotor strategies involving the use of a peripheral retinal region to replace the fovea (Figure 1). This region, referred to as the preferred retinal locus (PRL)7, is often adopted by patients in tasks involving fixation, reading, and face recognition. There is evidence of the PRL, in patients with MD, taking over oculomotor referencing duties of the fovea8,9. Further, changes in attention and cognitive control are observed in patients with central vision loss, suggesting a relationship between vision loss and cognitive functions10.

Figure 1. Illustration of the perceptual experience of individuals with healthy vision and macular degeneration patients with foveal scotoma. Foveal scotoma leads to central vision loss in patients with macular degeneration. Some individuals can partially compensate for the loss of visual input to the fovea by using a peripheral retinal location, defined as preferred retinal locus (PRL). In patients that developed a PRL, this is often used for eccentric fixation and during daily tasks. Retinal location, shape and size of the PRL can vary from person to person. Please click here to view a larger version of this figure.
While no gold standard intervention exists to recover vision loss or to compensate for loss of central vision, experimental approaches from optometry, occupational therapy and vision science are being tested to improve compensation through peripheral vision11,12. Oculomotor approaches focus on teaching patients to improve eye movement control and coordination, including teaching them to use a more adequate PRL11,12,13,14,15 while perceptual interventions focus on improving the general peripheral visual abilities or vision within the PRL, partially overcoming the limitation of peripheral vision16,17,18,19,20. Recent studies have used an eye-tracking based gaze-contingent display as a paradigm for the study of eye movements in central vision loss21,22,23,24,25,26,27,28,29. This approach, which utilizes a simulated scotoma (i.e., an occluder to obstruct the central region of the visual field) in healthy individuals (Figure 1), mitigates issues of recruitment and compliance, while providing high control on several parameters, such as the size and shape of the scotoma, thereby offering a promising alternative to the direct involvement of patients with MD. While there exists several differences between central vision loss and simulated scotoma30,31, some of the oculomotor behavior observed in the former, such as the development of a PRL, can be seen in the latter27,30,32, suggesting that some aspects of compensatory oculomotor strategies can be elicited by this gaze-contingent paradigm. Importantly, simulated central vision loss provides a broad framework for studying plasticity in both the healthy visual system and following central vision loss.
Here, we present the design, development, and use of a gaze-contingent framework that can be used to test perceptual, oculomotor, and attentional performances in healthy individuals and, with some modifications, in MD patients (Figure 2). We also detail the technical and psychophysical considerations that accompany gaze-contingent, peripheral training. A key technical challenge involves creating the perception of a smooth, short latency movement of the scotoma33. This short latency is obtained by selecting appropriate display devices, eye trackers, and operating systems34,35,36. Previous work has documented how each piece of hardware adds latency37 and strategies to reduce overall latency, accommodate blinks, and slow eye movements33. A novel aspect of our paradigm is the diverse set of training and assessment tasks within a single framework for perceptual research in both healthy and patient populations. The framework characterizes multiple levels of visual processing affected by central vision loss, specifically low-level vision, higher-level vision, attention, oculomotor control, and cognitive control. Preliminary tests conducted using a modified version of this approach showed evidence of improvement in visual acuity in both healthy controls and the patient population32.

Figure 2. Multidimensional approach to the study of plasticity in the visual system, and vision rehabilitation in Macular Degeneration. Illustration of interconnected dimensions such as visual perception, oculomotor, and cognitive control that contribute to visual processing and are affected in central vision loss. Please click here to view a larger version of this figure.