Veterinary Ophthalmology (2007) 10, Supplement 1, 63– 69 © 2007 American College of Veterinary Ophthalmologists Blackwell Publishing Inc Ocular melanosis in the Cairn Terrier: clinical description and investigation of mode of inheritance Simon M. Petersen-Jones, Janice Forcier and A. Lexi Mentzer Department of Small Animal Clinical Sciences, Michigan State University, East Lansing, MI 48824–1314, USA Abstract Objective To describe the clinical features of ocular melanosis in Cairn Terriers. Animal studied One hundred and fourteen Cairn Terriers diagnosed with ocular melanosis. Procedure(s) 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. Key Words: Cairn Terrier, dog, ocular melanosis, pigmentary glaucoma, secondary glaucoma Address communications to: Simon Petersen-Jones Tel.: (517) 353-3278 Fax: (517) 355-5164 e-mail: peter315@cvm.msu.edu INTRODUCTION Covitz et al. in 1984 described at a meeting of the American College of Veterinary Ophthalmologists a condition in Cairn Terriers characterized by ocular pigment proliferation and secondary glaucoma which they termed pigmentary glaucoma. 1 Since that initial description of seven cases a few additional case reports have appeared in the literature describing the condition in an additional 10 Cairn Terriers, and the term ocular melanosis has come into common usage. 2–4 From these case reports it is known that the condition is manifest as a progressive, bilateral proliferation of pigmented cells, primarily within the anterior uveal tract, and can result in the development of secondary glaucoma. The incidence of ocular melanosis within the Cairn Terrier breed is not known, although there appears to be increasing concern about it amongst Cairn Terrier breeders. A survey of members in 2005 by the Health Related Committee of the Cairn Terrier Club of America revealed that ocular melanosis was the second most common health issue of concern to the respondents. In an analysis of the incidences of glaucoma in pure-bred dogs reported to the Veterinary Medical Database, Gelatt and MacKay 5 found that the reported incidence of glaucoma in Cairn Terriers examined at the participating North American Veterinary College Veterinary Teaching Hospitals had risen from 0.51% (mean for all breeds 0.46%) between 1974 and 1983 to 1.82% (mean for all breeds 0.89%) between 1994 and 2003. This increased incidence of glaucoma elevated the Cairn Terrier from 23rd in the league table of glaucoma incidence in pure- bred dogs to 9th. The survey did not report the cause of glaucoma so it is not possible to know what proportion of