Quantifying functional impairment and metamorphopsia in a low vision population
Visual perception is required to interact with our environment on a daily basis. Pathological vision loss can disrupt perception and cause systematic functional changes. Quantifying these changes is essential to monitor deficits associated with visual disease, but measurement is complicated by retinotopic impairment, an overlap of symptoms, and influence from higher visual processes. Visual search provides a way to examine visual functioning in a ubiquitous task that involves an interplay between high-resolution central vision and low-resolution peripheral vision. We examined visual search performance in 12 participants with peripheral visual field loss (PVFL) and eight participants with central visual field loss (CVFL). Visual search behavior in PVFL participants was significantly different from age-matched controls with no field loss; yet oculomotor parameters were not significantly different. This suggests that PVFL impairs eye movement strategies, but not dynamics of oculomotor control. CVFL participants completed a visual search task with a set of image modifications designed to improve common perceptual deficits of CVFL patients. There was no significant benefit of image modification on performance, but a multivariate model accurately predicted performance on the basis of age, acuity and extent of field loss. Attempts to improve search may be more successful if they are tailored to the individual’s deficits. Metamorphopsia (visual distortion) often precedes visual field loss, may be caused by retinal layer displacement, and can be used to study the progression of retinal disease. A retrospective study of more than 7,000 Amsler grids showed systematic variations in the spatial pattern of distortion across different etiologies and concluded that metamorphopsia is a prevalent symptom that varies across disease type. However, a study of patient reported outcomes determined that metamorphopsia is under-reported in retinal disease patients, which may impact self-referral and clinical management. We also developed novel psychophysical methods to quantify metamorphopsia, yet found that measures across methods were uncorrelated. This suggests that metamorphopsia is not simply a consequence of pathological retinal displacement, but involves higher visual processes. Finally, we considered how metamorphopsia interacts with visual acuity and found a nonlinear relationship between the spatial properties of distortion and performance on a letter recognition task.