Abstract
Intraocular medulloepithelioma is a relatively rare tumour in horses which is difficult to differentiate from retinoblastoma. The rate of growth of this tumour has not been investigated so far. We present a case of a primary intraocular teratoid malignant medulloepithelioma in a four‐year‐old gelding that was unilaterally blind at presentation. Repeated examination revealed rapid growth of the tumour. After enucleation of the affected eye, the horse returned to its former level of performance without recurrence for 12 months postoperatively. The histological and immunohistochemical examination of the mass clearly confirmed the malignancy of the tumour. Clinicians should be aware of the potential malignant behaviour of intraocular neoplasias. Immunohistochemistry plays an important role in the final diagnosis.