Prevalence of ocular abnormalities in cats with hyperthyroidism

The purpose of this study was to investigate the occurrence of ocular abnor malities in hyperthyroid cats. One hundred hyperthyroid cats and 30 clinica lly normal, geriatric cats were studied. In both groups, ophthalmic examina tion was performed by use of slit-lamp biomicroscopy and indirect ophthalmo scopy after application of 1% tropicamide to dilate the pupil. Ocular abnor malities were common in both the hyperthyroid and euthyroid cats. Approxima tely 75% of all eyes were affected with 1 or more abnormalities, and the ra nge of;abnormalities involved all structures of the eye. Significant differ ences between the euthyroid and hyperthyroid cats were found in the prevale nce of prominent suture lines, nonpigmented deposits on the posterior lens capsule, hyperreflective ring around the optic nerve, and hyperpigmentation of the area centralis, but all of these abnormalities were more common in the euthyroid cats than in the cats with hyperthyroidism. Active retinal le sions were only observed in 3 hyperthyroid cats (3%). The results of this s tudy indicate that hyperthyroidism does not seem to be a frequent cause of abnormalities in the eyes of cats.