The Diagnosis and Management of Genetic Blinding Diseases

Blindness can develop for many reasons, either because parts of the eye, such as the cornea or the lens, become opaque, or because the retina, optic nerve, or central visual pathways in the brain are damaged. Glaucoma, cataract, and retinal degeneration are among the most common blinding diseases, and an underlying genetic defect is often suspected. This seminar deals specifically with the diagnosis and management of such blinding disorders.

1. Glaucoma
At present, glaucoma is defined as an optic neuropathy that is associated with increased intraocular pressure (IOP) and the loss of eye sight. Glaucoma can be primary (i.e., probably genetic) or secondary (e.g., caused by chronic uveitis, retinal detachment, or an intraocular neoplasm). In dogs, the most common form of glaucoma is primary. In cats on the other hand, glaucoma is mostly secondary. Primary glaucoma has been identified in well over 40 canine breeds, including the American Cocker Spaniel, the Chow Chow, the Shar Pei, the Boston Terrier, the Norwegian Elkhound, and the Basset Hound.
The clinical signs of glaucoma vary with the type and the stage of the disease. It is possible that both eyes show similar signs; however, in most dogs only one eye is affected first with the second eye developing clinical signs days, weeks, or months later. Early clinical signs include a dilated (mydriatic) pupil, mild transient corneal edema, and variable episcleral congestion. During the advanced stage of the disease the mydriasis and corneal edema are persistent. The globe will enlarge (buphthalmia), and the lens may luxate. Ultimately, the measurement of the IOP with a tonometer is the most important part of the eye examination (normal range: 10 to 20 mmHg). [...]