Coordination of Eye and Head Movements in Central Field Loss

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Age-related macular degeneration is the most common cause of vision loss in the central visual field, making central field loss (CFL) a major problem in the world today. Two-thirds of patients with CFL complain of vestibular problems, such as dizziness and instability, leading to a high incidence of potentially fatal accidents and falls. The problem is exacerbated by the patient population's advanced age, due to a documented decline in vestibular function in senescence. Vestibular deficits in CFL patients are likely due to miscalibrated or non- optimal stabilizing eye movements - many essential oculomotor behaviors are highly reliant on retinal input. Individuals with compromised vestibular responses have difficulties with visual field stability, navigation, and self- and external motion perception. These limitations are particularly true for CFL patients, whose visual acuity is already compromised and for whom the vestibular system may be the predominant source of motion information. Despite the importance of visual/vestibular interaction, these behaviors have not been comprehensively studied in CFL. This proposal seeks to address this gap. Evidence from the K99 stage indicates that individuals with CFL rely more on head movements for smooth pursuit than controls. Furthermore, these data support previous findings that head movement may improve smooth pursuit performance. Aim 1 of the R00 stage will extend these findings by directly addressing how vestibuloocular reflex (VOR) cancellation might play into the head-free smooth pursuit response. Further, this aim examines the effect of CFL on the angular VOR itself. The reflex has little foveal dependence. However, foveal vision is known to contribute to both VOR calibration and to its suppression when the head movement follows target motion. A deficit in any aspect of angular VOR will have consequences on the visual instability and vestibular discomfort of the affected individuals. Understanding these problems would inform necessary treatments in this population. Aim 2 examines the effects of CFL on translational VOR, a behavior that is fovea-dependent and essential when body movement is present. Determining the degree of its impairment and exact influences of CFL is key to understanding vestibular dysfunction due to CFL. VOR responses will be studied during passive and active motion. Previous research suggests fundamental differences in the processing of these two types of behavior, which indicates that they might be affected differently by central vision loss. If present, this dichotomy could have implications for how patients are advised and trained to interact with their environment while maintaining an active and productive lifestyle. ! !