Understanding and Treating Glaucoma

Presenter: Professor Ron Ofri, DVM, PhD Koret School of Veterinary Medicine, Hebrew University of Jerusalem

Glaucoma is a condition I don’t encounter too often, but when I do it is essential that I have all the appropriate and up to date information at my fingertips so I can act as quickly as possible to try to prevent any loss of vision and manage a patient’s pain.

This an area where ‘The Webinar Vet’ excels in offering regular updates on conditions encountered in practice and acts as a point of reference which can be accessed instantly. Last week’s veterinary webinar led by Prof. Ron Ofri did just this for managing and diagnosing glaucoma in dogs and cats.

Prof. Ofri led us seamlessly through understanding glaucoma, from classification to its diagnosis and management. It was explained how the classification of glaucoma can be clinically significant with primary glaucoma often requiring lifelong treatment with the contralateral eye also at risk. Whereas secondary glaucoma has the potential to be cured with the contralateral eye unlikely to be affected. Prof. Ofri also discussed classifying glaucoma as being either open or closed/narrow angle with all types of classification being able to be combined i.e. primary open angle glaucoma in the beagle.

Diagnosing glaucoma also featured significantly within the webinar including the measurement of intraocular pressure through tonometry with Prof Ofri reminding us not to press on the jugular vein whilst performing this technique as it will inevitably increase IOP. Clinical signs were also discussed with pain being a clinically significant finding, often presenting as severe in acute glaucoma but can be less noticeable in chronic disease.

Prof Ofri explained that even in chronic disease where the signs of pain are less evident, owners need to be convinced that pain is present in order to get them to move forward with treatment. In some cases of chronic glaucoma, where sight has been lost, this can mean enucleation. Prof. Ofri uses the analogy of a migraine to explain to owners the extent of pain these animals are in and, once treated, (often by enucleation) owners will often state how much younger and happier their pet appears.

Other clinical signs discussed included fixed dilated pupils, corneal oedema, lens luxation, red eye and striate keratopathy. This is caused by stretching of the collagen and is seen as white lines across the surface of the eye being pathognomonic for glaucoma. Buphthalmos is also seen as a result of the eye stretching as a defence mechanism to spread the elevated intraocular pressure over a greater surface area. Glaucoma will also lead to retinal atrophy and blindness due to ischeamia and mechanical damage to the optic nerve. Ciliary body atrophy and phthisis bulbi will eventually develop after animals have suffered over a long period with glaucoma.

Medical and surgical treatment options were discussed with prostaglandin (PG) analogues (Xalatan) being the current topical drug of choice in both dogs and humans and works by increasing the unconventional outflow of aqueous humour. For this reason it can be used regardless of the state of the angle of the cornea but is contraindicated in cases of uveitis where the eye has already been flooded with prostaglandins. PG analogues are however ineffective in cats as there are no PG receptors present in this species with carbonic anhydrase inhibitors (dorzolamide) being the drug of choice.

This is a veterinary webinar you need to watch to really appreciate the amount of practical up to date information on glaucoma delivered in the space of an hour.  If, however, you don’t get chance to log in, Prof. Ofri was adamant on one point which, if nothing else, must be taken on board. If a patient presents with unilateral glaucoma which is not an obvious secondary glaucoma, the contralateral eye MUST also be treated. After all the most important eye to protect is the one with vision and this will invariably be the eye yet to develop glaucoma.

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