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Alexandra S. Almazan, Susan Tsai, Susan S. Lee, Huajiang Li, Paul Conforti, Sherri Decker, James A. Burke, Michael R. Robinson; Angle Narrowing with Topical Latanoprost in Normal Dogs. Invest. Ophthalmol. Vis. Sci. 2012;53(14):5029. doi: https://doi.org/.
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Glaucoma is one of the most common causes of irreversible blindness in dogs. Primary angle closure glaucoma (PACG) is at least 8 times more frequent than open angle glaucoma and initially presents with a unilateral, acute episode of high IOP elevation, often resulting in blindness in this eye. Approximately 50% of dogs will have an angle closure attack in the fellow eye within 1 year. The fellow eyes are frequently prophylaxed with topical glaucoma medication in the hope of prolonging or preventing the angle closure and IOP elevation. Topical latanoprost can lead to an extreme miosis in dogs and we sought to determine the effect on angle size using anterior segment OCT.
Under an approved Animal Care and Use Committee protocol, biometric gonioscopy was performed in 35 normal beagle dogs using anterior segment OCT (Ziess, Visante) under general anesthesia. In brief, the one randomly selected eye of each dog was scanned with the scan plane perpendicular to the limbus in the temporal quadrant. One drop of 0.005% latanoprost was placed in this eye and the OCT scan was repeated after ~30 minutes. Images were imported into ImageJ (National Institutes of Health, Bethesda, MD) and the angle opening distance from Schwalbe’s Line (AOD-SL) was measured. The AOD-SL is a key cross sectional anatomical parameter and measures the perpendicular distance from Schwalbe’s Line to the iris. The paired t-test was used to test the difference between pre- and post-dosing in AOD.
The pre-dose latanoprost AOD: 0.877 +/- 0.200 mm, post-dose latanoprost AOD: 0.699 +/- 0.185 mm (p-value < 0.001)
The exact mechanism by which prophylactic therapy using a variety of classes of anti-hypertensives reduce the rate of a PACG attack is not clear. The natural history of PACG in some dogs involves a progressive narrowing of the angle with the peripheral iris occluding aqueous outflow. Our study results demonstrate that topical latanoprost may significantly narrow the iridocorneal angle in normal beagles and should be used cautiously when prophylaxing fellow eyes for PACG when iris apposition to the outflow structures is suspected. Studies using biometric gonioscopy in goniodysgenic dogs are warranted to understand the changes in iridocorneal morphology that occur in PCAG and to further explore the role of prophylactic therapy in the fellow eye with different classes of anti-glaucoma medications.
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