This lecture will review the most common systemic diseases causing ocular changes in small animals. Diabetes mellitus in dogs regularly causes cataracts within the first year or two following diagnosis. Systemic hypertension in cats can lead to retinal detachment and acute blindness. Anterior uveitis is often associated with systemic processes such as infections or neoplasia, however it can also be caused by local immune mediated reaction to the uveal tissue. Regardless of the specific underlying systemic diseases affecting the eyes, all can result in significant morbidity or mortality. The ability of the clinician to use the eye as a “window” to the rest of the body can be lifesaving.