Dogs Eyes Dilated. In elderly dogs, the appearance of dilated pupils may be due to a condition known as iris atrophy where degeneration of iris sphincter muscle responsible for constructing the pupil fails to work properly. In some cases, the abnormal pupil may be the one that is.
Dilation occurs in the dark or when a drop is applied to the eye to cause the pupil to dilate. Anisocoria is a sign of a disease or condition, therefore there can be several different causes, including: Horner's syndrome) glaucoma (the affected eye will have an increased pressure within the eye and will be dilated) degenerative changed to the iris tissue that can happen with aging;