Page 153 - ONLINE PROCEEDING BOOK WSAVA 2017
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Emergency management
If a dog develops acute glaucoma, the goal is to reduce the IOP as soon as possible to prevent permanent optic nerve damage and loss of vision. The most commonly used strategies to decrease IOP in acute glaucomas include hyperosmotic agents, prostaglandin analogues.
Topical prostaglandin analogues decrease IOP by increasing out ow. These are very potent IOP reducing medications and are often very effective in rapidly reducing IOP. Prostaglandin analogues might exacerbate uveitis and causes miosis and are contraindicated in patients with anterior lens luxation, feline aqueous humor misdirection syndrome and other causes of pupillary block glaucoma as miosis will exacerbate IOP elevation in such cases. Therefore they should not be used if any of these conditions cannot be ruled out. Latanoprost 0.005% (Xalatan) is currently more commonly employed in veterinary medicine (compared to bimatoprost or travaprost) and is usually administered every 12 hours.
Systemic hyperosmotic agents: These medications can be used to treat acute glaucoma by dehydrating the vitreous to decrease IOP. The effect of these agents are transient only. Hyperosmotic agents are contraindicated in patients with cardiovascular disease or renal insuf ciency. Mannitol is safe to use in diabetics whereas glycerol should not be used in diabetics. Nausea is common in patients treated with glycerin. They are primarily used to quickly reduce IOP in acute glaucoma and can help allow time for topically applied anti- glaucoma medications to take effect. The agents that are most commonly used are mannitol (1-2 g/kg) and oral glycerol (1-2 g/kg). Ocular hypotensive effects occurs within 30 minutes and may last for 6-10 hours.
Aqueocentesis can be performed on an anesthetized patient by a veterinary ophthalmologist if prostaglandin analogues and hyperosmotic agents are contraindicated or not effective, but the effect of this is often very
short and there is a risk of hemorrhage or damage to intraocular structures with this technique.
Chronic management
Chronic management can include both medical and surgical therapies and the target IOP should ideally be <15 mmHg as studies suggest that even high normal IOPs can be damaging in eyes who have had previous pressure spikes. The most commonly used strategies to decrease IOP in chronic glaucomas include carbonic anhydrase inhibitors, beta-blockers and prostaglandin analogues.
Prostaglandin analogues are the most potent hypotensive agents in this group and are usually give every 12 hours (see above).
Topical carbonic anhydrase inhibitors (CAI’s) decrease production of aqueous humor. These include
An Urban Experience
dorzolamide (Trusopt) and brinzolamide (Azopt) and
are administered every 8 hours. Dorzolamide can
be combined with timolol to form Cosopt which is administered every 12 hours to obtain similar hypotensive effects as TID dosing of dorzolamide alone. Although these drops are typically safe to use local irritation can occur in some patients.
Systemic CAI’s includes acetazolamide and methazolamide and reduced production of aqueous humor. These medications cause systemic acidosis, which can lead to excessive panting and vomiting, and diarrhea. They can also cause mild hypokalemia. They are usually given 2-3 times daily. Methazolamide (3-4 mg/ kg PO BID) is often preferred over acetazolamide since the latter can have more severe adverse effects.
Beta-blockers lowers IOP by reducing aqueous humor production, although the exact mechanism has yet to
be elucidated. They include timolol and betaxolol. They should be used 2-3 times daily. Adverse effects include bradycardia and they should be avoided in asthmatic patients. Timolol 0.5% is the most commonly employed in veterinary medicine. It is nonspeci c, meaning it blocks both B1 and B2 receptors. Timolol has been shown to lower IOP in dogs, cats, and horses. However, potency is minimal when used alone in comparison with CAIs and prostaglandin analogues in veterinary species.
Surgical management is often combined with medical management when medical management is starting
to fail. If the animal is still visual surgical management strategies can include gonioimplants, iridenclesis,
and cyclodialysis. In endstage glaucoma where the
eye is blind and painful enucleation or evisceration
and placement of an intrascleral prosthesis can be performed. Intravitreal injection of gentamicin or cidofovir is usually reserved for cases in which surgery cannot be performed.
Prophylactic medication: In a multicenter clinical topical 0.5% betaxolol twice daily or topical 0.25% demecarium bromide once daily and a topical corticosteroid once daily signicantly delayed or prevented the onset of glaucoma in the second eye in dogs diagnosed with primary glaucoma in one eye. Untreated control dogs developed glaucoma in the second eye earlier (median: 8 months) than eyes treated with prophylactic medication (median: approximately 31 months).
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