Ocular melanosis in the adult Cairn Terrier population within the United Kingdom

Prospective investigation to determine the prevalence of ocular melanosis in adult Cairn Terriers within the United Kingdom using a previously established staging scheme.

Ophthalmic assessment was performed on adult Cairn Terriers, recruited from various geographic locations within the United Kingdom. Examination included gonioscopy, rebound tonometry, slit lamp biomicroscopy, and indirect ophthalmoscopy, performed by one examiner (AM).

A total of 93 dogs were examined, including 52 females and 41 males, aged between 15 months and 16 years 4 months. Sixty of 93 dogs (64.5%) were >7 years of age. Nine of 93 dogs (9.6%) demonstrated changes consistent with ocular melanosis. Four of 9 (44.4%) had Stage 1 disease and 5 of 9 (55.6%), Stage 2. Stages 3 or 4 were not identified in any dogs. Mean intraocular pressures in affected and unaffected dogs were 14.7 mmHg (range 12-17 mmHg) and 12.8 mmHg (range 5-21 mmHg), respectively. Incomplete pupil dilation was noted in affected dogs following pharmacologic mydriasis.

Ocular melanosis was identified in approximately 10% of examined dogs, over half were dogs of breeding age (<7 years of age). It is possible that Grade 1 disease could go undetected, prior to obvious scleral pigment accumulation (Grade 2 disease). It is therefore recommended that dogs undergoing pre-breeding screens have pre-dilation assessment of the anterior segment using slit lamp biomicroscopy with subsequent gonioscopy to clearly assess for circumferential thickening of the iris base that might otherwise go undetected. Additionally, regular reassessment of breeding dogs is advised as disease progression could be rapid.