Claude, a delightful Tonkinese cat presents to you because his owner is concerned at a difference in colour between the two irises. Intraocular pressure is 15mmHg in both eyes. What is happening here and what might be the reason for the difference between this eye and the other where the iris is uniformly blue?
Here is the eye as it was a month ago with slightly less in the way of focal iris neovascularisation, the cause of the colour change. This could be rubeosis iridis (iris neovascularisation in response to ischaemic change in the iris or retina) but the similarity in iop between the eyes suggests no inflammatory process here and the retina is unremarkable. The other possibility is a neoplastic process in the iris or the ciliary body behind it. Ultrasonography shows a moderately thickened iris but no ciliary body mass. What would your next diagnostic step be? Give me an e-mail and let me know please!