Objective: To describe the clinical features of ocular melanosis in Cairn Terriers.
Animal studied: One hundred and fourteen Cairn Terriers diagnosed with ocular melanosis.
Procedures: A complete eye examination was performed on each dog. Four dogs (and two unaffected control dogs) underwent a high frequency ultrasound examination of the anterior segment. The pedigrees of affected dogs were analyzed.
Results: Forty-four (38.6%) dogs were male and 67 (58.7%) female; the sex of three dogs (2.6%) was not provided. A four-stage grading system of the ocular changes was developed. There was a variable age of onset, and the earliest change was a dark-colored thickening of the iris root. This was followed by the development of episcleral/scleral pigment plaques, release of pigment into the aqueous and deposition in the drainage apparatus, particularly ventrally. Secondary glaucoma developed in the most severely affected dogs. A slow progression of pigmentation in the tapetal fundus was observed and in some dogs pigment on the surface of the optic nerve head was seen. Three dogs developed uveal melanocytic neoplasms. Pedigree analysis suggested a possible autosomal dominant mode of inheritance.
Conclusions: Ocular melanosis is an inherited, probably autosomal-dominant condition with a variable age of onset and rate of progression. It results in a thickening and pigmentation of the iris, release of pigmented material into the aqueous, pigment deposition in the sclera/episclera, and to a lesser extent posterior segment pigment deposition. Following extensive pigment deposition in the aqueous drainage pathways it can result in secondary glaucoma.