Purpose: To describe the electroretinographic (ERG) and spectral domain-optical coherence tomographic (SDOCT) features of the retina of clinically normal horses of varying ages in order to assess the effect of age on equine retinal structure and function.

Methods: Forty-eight eyes of 24 horses (ages 6-28 years) free of clinical ocular pathology will undergo standing sedated full field ERG, high resolution retinal imaging with a Bioptigen SD-OCT, and fundus photography with a RetCam. Retinal structure as determined by SD-OCT and retinal function as determined by ERG will be compared across 3 age groups (<10 years, 11- 20 years, >21 years).

Expected Outcome: Based on age-related decreases in ERG b-wave amplitudes but maintenance of uniform retinal thickness documented in other species, it is expected that horses also undergo age-related decreases in ERG b-wave amplitudes but maintain consistent retinal thickness. This study will generate normal data for retinal layer thickness and ERG amplitudes of horses of various ages.

Significance: Perceived changes in vision based on spooking or balking behaviors is a common reason that horses are presented for ophthalmic examination. In the absence of ocular abnormalities on clinical examination, we rely on advanced diagnostics (ERG, streak retinoscopy) to determine if the eyes could in fact be the source of such behavioral changes. While several equine ERG protocols have been described, the effect of aging on the equine ERG has not. OCT represents a major advancement in our ability to diagnose and monitor retinal diseases, though to date, a single study on OCT of the normal equine retina has been published, with age-related changes not yet assessed. This project aims to provide data on structural and functional changes in the aging equine retina.