A survey of ocular abnormalities in miniature horses.

Objective: To determine the incidence of ocular abnormalities in miniature horses.

Design: Descriptive study.

Animals Studied: Fifty-three miniature horses.

Procedure: Ophthalmic examinations were performed using diffuse and focal illumination, slit-lamp biomicroscopy and indirect ophthalmoscopy. Coat color, mane and tail color, age and gender were recorded with results of ophthalmic examination.

Results: Ocular abnormalities detected most frequently consisted of cysts arising from the posterior iris, ciliary body, and peripheral retina, curvilinear streaks of retinal pigmented epithelium extending from the peripheral temporal retina, and retinal dysplasia (folds). One miniature horse also had multiple ocular abnormalities (cornea globosa, goniosynechiae, decreased or absent and pupillary light reflexes, miotic and dyscoric pupils, iris hypoplasia, and epinuclear cataract). Ocular abnormalities were observed in horses that had a flaxen or white mane and tail color and a chocolate coat color.

Conclusions: Abnormal ocular phenotype detected in eyes of Miniature Horses was similar to multiple congenital and hereditary ocular abnormalities reported in the Rocky Mountain Horse. Phenotypic ocular developmental abnormalities and coat, mane and tail color were most compatible with a heterozygous or homozygous effect of the Silver Dapple locus.