Characterization of ocular melanosis in dogs

Cairn Terriers can suffer from a hereditary form of bilateral ocular melanosis (OM). It causes the accumulation of large and darkly pigmented melanocytes in the anterior uvea which may damage ocular structures. The progression of this pathology is slow but the cells can migrate to other structures and cause thickening of the iris root, form plaques in the sclera/episclera and/or invade the meninges of the optic nerve. Secondary glaucoma is also described when cells are deposited in the drainage angle.

In order to investigate the type of cells causing melanosis and learn more about their invasive behavior, the authors analyzed 48 dogs’ ocular globes. 27 were from 18 dogs affected by OM and 21 were from clinically normal animals. The majority of the eyes were examined via uveal culture and 6 OM-affected globes were submitted for immunohistochemical examination.

The large, heavily pigmented cells in dogs with OM were found to be mostly melanocytes with a significantly increased production of melanin. A higher proliferation or invasiveness in melanocytes from OM-affected eyes was not observed. This could be because in vitro assays weren’t able to replicate the necessary physiological conditions that exist in OM affected eyes.

In the authors’ view further studies are needed and should focus on RNA sequencing and gene expression. This will allow for a better understanding of the underlying mechanism of this disease.

In Dawson-Baglien EM, Noland EL, Sledge DG, Kiupel M, Petersen-Jones SM. Physiological characterization of ocular melanosis-affected canine melanocytes. Vet Ophthalmol. 2018