Optic disc astrocytoma in a horse.

This research article discusses an unusual case of a horse with an optic disc astrocytoma, a type of brain tumor that originates in the optic nerve. Through detailed examination, the scientists identified the tumor and subsequently euthanized the horse for further investigation of the eye and optic nerve.

Introduction

• The article begins by outlining the relative infrequency of primary intraocular neoplasms (or tumors) in domestic animals. Such tumors are typically malignant melanomas of the uveal tract, while nonpigmented intraocular tumors and metastatic-origin ones are less common.
• The paper notes that tumors of the optic nerve – the nerve that carries visual information from the retina to the brain – are extremely rare in both humans and animals. Existing literature on optic nerve gliomas (tumors formed from glial cells) in animals is scant.

Case Report

• The study presents the case of a mare which was examined as a part of an equine ocular fundus investigation. While the horse’s reflexes and right ocular fundus were deemed normal, an oval-shaped mass was found on the left optic disc. Despite the mass, the mare’s vision was normal. Following the diagnosis, the horse was euthanized.

Gross and Histological Examination

• Following euthanization, the horse’s eye was removed and fixed in formalin for detailed examination. The external gross examination of the eye and the optic nerve indicated normality.
• Once the eye was sectioned, researchers noticed an oval neoplasm located adjacent to the optic disc, with a shiny smooth surface. The tumor was attached to the retina at the margin of the optic disc, protruding into the vitreous body, a clear gel that fills the space between the lens and the retina of the eyeball.
• The extracted sections of the eye were embedded in paraffin, a solid, white substance used in laboratory procedures to trap water and prevent tissue parts from drying out, and then stained using multiple techniques for further histological examination.
• The histological examination led to the observation of a dense, circumscribed, round-oval neoplasm adjacent to the optic disc. The tumor projected from the inner layers of the retina into the vitreous body.

The study highlights the rarity and clinical significance of such tumors, supplementing the limited available literature on the subject.