||OBJECTIVE: To record the prevalence and document the types of eye disease in population of Thoroughbred racehorses in Victoria, Australia. DESIGN: Prospective study. ANIMALS: Two hundred four Thoroughbred racehorses. PROCEDURE: All horses and both eyes were examined at four metropolitan and two country racing stable complexes. Ophthalmic exam was performed following dark adaptation with a transilluminator, biomicroscope, and direct ophthalmoscope. Intraocular pressures were measured when indicated. Both pupils were dilated with tropicamide when indicated. RESULTS: One hundred eighty-two (89.2%) flat-racing and 22 (10.8%) jump-racing (hurdle or steeple) horses were examined. Age range: 2-9 years (mean 3.7 years, median 3); 97 (47.5%) male-neuter, 74 (36. 3%) female, 33 (16.2%) male. Potential vision-threatening eye disease was present in 15 (7.4%) different horses: complete lenticular cataracts 3, posterior lens luxation and cataract 1, large peripapillary 'butterfly' inactive lesions 3, large peripapillary 'butterfly' active lesions 2, peripapillary focal inactive 'bullet hole' chorioretinal lesions (> 20) 5, optic nerve atrophy 1. Non-vision threatening eye disease was present in 117 (57.4%) different horses, involving one or more ocular structures: lower eyelid scars 3; periocular fibropapillomatous disease 1; third eyelid squamous cell carcinoma 1; corneal scars 6; corneal band opacity 2; anterior iris synechia 1; developmental cataracts 36 (17.2%); peripapillary focal inactive 'bullet hole' chorioretinal lesions (< 20) 103 (50.0%); linear peripapillary hyperpigmentation bands 16 (7.9%). Unusual variations of normal ocular anatomy and colobomata was recorded in 11 (5.4%) different horses: granular iridica hypoplasia 3, granular iridica hyperplasia 2, multilobular granular iridica cyst 1, microcornea 1, hyaloid remnant 1, rotated optic nerve head 1, coloboma of the lens 1, atypical coloboma of the retina 1. CONCLUSIONS: This survey demonstrates that the prevalence of vision-threatening eye disease in racing horses may be greater than previously perceived, and highlights the importance of ocular examination within any routine physical examination of horses.