This 9 year old female Shire horse was referred as the veterinary surgeon was concerned about this lesion in the eye. What is it, is there any reason to worry and what measures might be taken to deal with it if it were a problem?
This an iris cyst, in this case probably developing from one of the corpora nigra given its position. Such lesions rarely cause a problem to the animal although may be associated with headshaking or visual impairment if large. Deflation with an Nd-YAG laser has been reported (Gilger et al: Neodymium:yttrium-aluminum-garnet laser treatment of cystic granula iridica in horses: eight cases (1988-1996). J Am Vet Med Assoc. 1997 211:341-3) although aspiration with a wide-bore needle is also readily acheieved. The only problem there is that more often than not these are attached to the iris, a situation not seen in the dog were these are common and, when present in large numbers, can lead to glaucoma. Solitary ones as shown here can happily be left well alone (note also the darker melanocytoma ventrally here, a possible differential diagnosis for an iris cyst and the posterior polar subcapsular cataract at the confluence of the suture lines in the background.