# Intraocular Tumors in Horses: Diagnosis, Tumor Classification, Oncologic Assessment and Therapy

## TL;DR

This paper reviews intraocular tumors in horses, focusing on diagnosis, classification, and treatment options, highlighting the lack of therapeutic strategies and the potential for comparative oncology.

## Contribution

The paper provides a clinicopathologic classification of intraocular neoplasia in horses and emphasizes the need for systematic oncologic assessment.

## Key findings

- Intraocular tumors in horses are rare and often diagnosed through clinical exams and imaging.
- Medulloepithelioma and uveal melanocytic neoplasia are the most common types in horses.
- Current therapeutic options for intraocular tumors in horses are limited and require further investigation.

## Abstract

Intraocular malignant neoplasia is a rare condition in horses and only single case reports exist. This review contains a systematic overview of the current literature and aims to provide a clinicopathologic classification of the currently described intraocular neoplasia. This seems important for any consideration concerning therapy and prognosis. Diagnosis of intraocular neoplasia can be achieved with clinical ophthalmic examination, supported by basic medical imaging techniques. A systematic oncologic workup and tumor staging seem to be rarely undertaken in equine ophthalmology. This review emphasizes the importance of these aspects and demonstrates the current lack of therapeutic options in equine ophthalmology as well as the comparative oncology perspective. The developments in human and small animal medicine seem to be promising, although some limitations remain unsolved.

Intraocular neoplasia in horses is rare and only few case reports and small case series exist. Intraocular neoplasia has various clinical signs and includes important differential diagnoses in ocular disease. This narrative review of the current literature aims to provide a clinically relevant overview and classification of intraocular tumors in horses and adds a comparative oncological perspective concerning diagnosis, treatment and future considerations. The available clinical and imaging examination techniques allow for a reliable and differentiated investigation of the tumor, even in the standing horse, using high-frequency ultrasound or optical coherence tomography, which have gained importance in equine ophthalmology. Sectional imaging techniques, in particular computed tomography, are suitable for the examination of the peribulbar, retrobulbar and orbital structures. Differentiated diagnostics including precise tumor staging (TNM: tumor, node, metastasis) are essential for a general prognostic and therapeutic assessment. The embryologic and anatomic tissue origin of the neoplasm is the basis for clinicopathologic classification. Medulloepithelioma and uveal melanocytic neoplasia are the most common intraocular tissue formations occurring in horses. Whereas melanocytic neoplasia of the iris can be treated surgically, neuroepithelial tumors regularly lead to bulbus extirpation. Other primary intraocular neoplasms are sporadically reported, as well as intraocular metastasis of systemic neoplasia. Chemotherapy and radiation therapy are not currently used to treat intraocular neoplasia in horses and need to be further investigated, especially regarding the latest developments in human and small animal medicine. In addition, horses and dogs may serve as models for human oncologic research.