VN April 2023

Vetnuus | April 2023 38 Regulars I Ophthalmology Column This month’s Vetnews theme is Exotics, so we will concentrate on some useful concepts to know regarding rabbit eyes and look at three common problems encountered in rabbit ophthalmology, namely Dacrocystitis, Cataracts and Corneal ulcers . General Concepts : • Rabbits have laterally positioned and well-exposed eyes, making them vulnerable to trauma. • A single lower lacrimal punctum may bifurcate into 2-3 ducts that then fuse again to form the nasolacrimal duct. This lower punctum can be cannulated. • The retina has a merangiotic blood supply meaning the blood supply exits via the optic nerve head. It then only spreads medially and laterally over the retinal surface, but the rest of the fundus does not have visible retinal blood vessels. • The optic nerve head of the rabbit is very myelinated, and the myelin spreads medially and laterally and can be clearly visible on direct ophthalmoscopy. • The rabbit has a band of the retina containing a high density of photoreceptors ventral to this vascularized strip, allowing it to see at a higher resolution along the horizon, something highly valuable for a prey species. • The rabbit cornea is very thin [400 microns], so any form of debriding, diamond head burring or a striate keratotomy should be performed with excellent magnification only. • The blink rate of a rabbit is very low at 10-12/hr. • A large retrobulbar orbital venus plexus is present that needs to be avoided when performing an enucleation in the species. Dacrocystitis : The nasolacrimal duct in this species begins with a single punctum at the medial ventral eyelid and then courses across the roots of both molar and incisor teeth. Any pathology or maxillofacial bone abnormality, molar tooth root, abscess, or overgrown incisor teeth may result in problems associated with the nasolacrimal duct pathology resulting in dacryocystitis or epiphora. Exotics – Rabbits Dr Antony Goodhead, Specialist Veterinary Ophthalmologist, Johannesburg and Cape Animal Eye Hospitals, www.animaleyehospital.co.za [Ack: Google Images]