Today's Veterinary Practice

MAR-APR 2018

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43 MARCH/APRIL 2018 ● TVPJOURNAL.COM FEATURES efficacy, water should be withheld for 4 hours after hyperosmotic treatment. 5 ■ Mannitol significantly reduces IOP within 15 minutes of administration and can remain effective for 6 to 10 hours. ■ Mannitol can be used safely in most dogs but should be used with caution in dogs with cardiac or renal disease, or in dehydrated patients. ■ I usually begin with 1 g/kg IV over 30 to 45 minutes. IOP should be measured at the end of the infusion to assess for efficacy. ■ If the IOP remains elevated at >25 mm Hg, an additional 1 g/kg IV dose may be given. ■ Monitoring of electrolytes should be considered. Prostaglandin Analogs Prostaglandin analogs lower IOP primarily by increasing AH outflow via their action on iris and ciliary body musculature. They induce a profound miosis and may physically open the ICA and improve flow. Prostaglandin analogs should be avoided in cases of glaucoma secondary to anterior lens luxation or severe uveitis. 6–8 ■ Latanoprost (Xalatan [ xalatan.com ]) results in a dramatic decrease (about 45%) in IOP within 20 minutes. The duration of effect is 8 to 12 hours, although this can vary between dogs. Additional doses may be given every 15 to 20 minutes if the initial response is insufficient. If the IOP remains >25 mm Hg after 3 doses/1 hour of treatment, alternate methods of IOP reduction should be attempted. Anterior Chamber Paracentesis Removing AH from the anterior chamber is a reliable method to quickly reduce IOP ( FIGURE 5 ). Depending on the clinician's skill level and the temperament of the patient, this procedure can be performed awake or with mild to moderate levels of sedation. The duration of effect of paracentesis varies widely, and additional hypotensive methods should be instituted. ■ Rinse the ocular surface with a dilute solution of povidone–iodine (1:20 diluted in saline). ■ Instill topical anesthetic. ■ If the patient is sedated, place a lid speculum and stabilize the globe with small, toothed forceps. In my opinion, when used without sedation these instruments cause undesired patient distress. ■ Use a small-gauge needle (30-, 27-, or 25-gauge) without a syringe attached. ■ Insert the needle at the dorsolateral limbus and direct it in a plane parallel to the iris; take caution not to touch the corneal endothelium, iris, or lens. ■ Allow the hub of the needle to passively fill; 1 to 3 drops of AH can spill over. Do not use suction. ■ Slowly remove the needle and measure the IOP immediately. ■ Note that the desired IOP is <15 mm Hg; repeat the process if necessary. FIGURE 5. Anterior chamber paracentesis. The left eye of a 6-year-old male castrated cocker spaniel with acute glaucoma is undergoing anterior chamber paracentesis. A 30-gauge needle has been inserted at the dorsolateral limbus and directed in a plane parallel to the iris. No syringe is attached, and aqueous humor is allowed to passively fill the needle hub. In this procedure, care should be taken not to touch the corneal endothelium, the iris, or the lens with the needle tip. A dog with significant anterior uveitis and an IOP in the normal range should raise great concern for impending glaucoma.

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