No additional investigations were performed and the animal was euthanized. At death, the local veterinary surgeon sampled the submandibular lymph node, which appeared enlarged. This tissue was submitted for microscopic examination and revealed metastatic spread of the tumor. In the horse intraocular primary or secondary neoplasms are very rare. Embryologic invagination of the optic cup results in a bilayered medullary epithelium with the inner layer forming the iridial pigmented epithelium, ciliary body non-pigmented epithelium and the neurosensory retina, while the outer layer forms the outer iridial pigmented epithelium, ocular ciliary pigmented epithelium, iridal dilator muscle, ciliary pigmented epithelium, and the retinal pigmented epithelium.
Ciliary tumors developing from more differentiated cell types form adenomas or adenocarcinomas.
Medulloepithelioma of the iris and ciliary body in a horse. Gelatt KN, 2nd ed. Gelatt KN, 2nd ed., p. 598. Malignant medulloepithelioma of the optic nerve in a horse. Ocular medulloepithelioma in a thoroughbred.