Glaucoma – Rabbit

Introduction

The bu gene is common in New Zealand White rabbits, causing a dysplastic iridocorneal angle where drainage is very poor. A useful paper on the condition is Ueno and colleagues report on histopathological changes in iridocorneal angle of inherited glaucoma in rabbits (Graefes Arch Clin Exp Ophthalmol. 1999; 237: 654 - 660)

Clinical Signs

Clinical signs include scleral congestion. A tonometer may be used in rabbits but rabbits have to be restrained in true lateral recumbency to obtain an accurate reading and the thin nature of the cornea means that if the Tonopen XL is used the flowing corrective formula must be applied:

True IOP (mmHg) = 1.12(Tomopen value) + 3.07

Normal intraocular pressures are between 15 and 23 mmHg whereas those of between 26-48 mmHg are diagnostic of glaucoma (Williams 2006). The dilated pupil that accompanies glaucoma may not be so obvious if uveitis is present and in any case may be difficult to assess as corneal oedema may be present. Buphthalmos and exposure keratitis are apparently a sequel to glaucoma in rabbits.

An emerging clinical precursor of glaucoma in rabbits is Encephalitozoon cuniculi infection leading to the formation of a white mass within the iris. It is important to assess the condition very carefully and to rule out the presence of uveitis.

Treatment

Lawton (1993) says that the use of Daranide® should be avoided, whereas Williams (2006) says that medical treatment is rarely effective or necessary. The treatment recommended by Lawton involves the injection of gentamycin into the vitreous as it destroys the ciliary body and the retina and stops vitreous production.

References

• Lawton M P C (1993) Procs BVZS Autumn Meeting ZSL 4/12/93
• Ueno et al (Graefes Arch Clin Exp Ophthalmol. 1999; 237: 654 - 660)
• Williams D L (2006) Ophthalmology in BSAVA Manual of Rabbit Medicine and Surgery eds Meredith A and Flecknell P, 2nd Edition 2006, published by BSAVA Quedgley Glocs