Rubeosis iridis and iris bombe in a cat

 

Photograph of the cat showing diffused thickening of the iris and emergence of new capillaries on the iris that are non-radially directed. Note the posterior synechiae appearing as thin fibrous links between the iris and the lens circumferentially (white arrowheads). Also, note the diffuse melanosis of the iris (*) towards the medial canthus. A strand of hair is seen stuck on the cornea which is an insignificant finding. The two white patches on the pupil are the reflections of the background light

Rubeosis iridis is the neovascularization along the surface of the iris. Normal vasculature of the iris lies in the stroma of the iris and is radial in orientation, whereas neovascularization appears on the surface of the iris and is irregularly oriented. This is also known as a pre-iridal fibrovascular membrane.

The iris rests typically on the anterior lens capsule and an inflamed iris invariably 'leaks' fibrin strands leading to adhesions between the iris and the anterior lens capsule. If this posterior synechia is present circumferentially like what was noticed in this case, it is termed iris bombe. 

The cat whose case is discussed above was presented with a complaint of pawing at its left eye intermittently for a fortnight. The IOP recorded in the left eye was 42mm H2O, significantly higher than the right eye which recorded 16mm H2O. 

The cat was prescribed topical Latanoprost 0.005% eye drops and oral acetazolamide at 7mg/kg every 8 hours to quickly reduce the IOP. Topical Moxifloxacin eye drops which were already prescribed were also continued. 

Tentative Diagnosis - closed-angle glaucoma secondary to iridal melanoma/lymphoma.  

The cat was never brought in for a review after the initial visit. One study revealed that about 48% of cats with lymphoma showed ocular lesions. The tentative diagnosis of lymphoma was made based on this finding alone. A very likely differential would be an iris melanoma considering the lesions were unilateral. A definitive diagnosis of the condition couldn't be made because the client never turned up. 

References 

1) Nerschbach, V., Eule, J. C., Eberle, N., Höinghaus, R., & Betz, D. (2016). Ocular manifestation of lymphoma in newly diagnosed cats. Veterinary and comparative oncology, 14(1), 58–66. https://doi.org/10.1111/vco.12061. 

2) Maggs, D., Miller, P., & Ofri, R. (2017). General Pathology of the Eye. In Slatter's fundamentals of veterinary ophthalmology (2nd ed., pp. 60-78). Saunders. 

3) Stiles, J. (2013). Feline Ophthalmology. In K. N. Gelatt, B. C. Gilger, & T. J. Kern (Eds.), Veterinary ophthalmology: Two volume set (pp. 1477-1580). John Wiley & Sons.