Today's Veterinary Practice

MAR-APR 2018

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39 MARCH/APRIL 2018 ● TVPJOURNAL.COM FEATURES Secondary Glaucoma Secondary glaucoma ( FIGURE 2 ) results from a physical obstruction to AH drainage, usually occurring at the ICA or pupil. The ICA can become obstructed with cellular debris (red blood cells, white blood cells, tumor cells) or inflammatory proteinaceous debris. The pupillary flow of AH may be obstructed by iris adhesions to the lens (posterior synechia) or an anteriorly luxated lens. Certain breeds, such as terriers, Chinese crested dogs, and the shar-pei, are predisposed to anterior lens luxation because of an inherited abnormality in the lens zonule suspension system. Acute glaucoma in these breeds should prompt the clinician to look closely for an anterior lens luxation. Duration of Glaucoma Acute Glaucoma: This type of glaucoma ( FIGURE 3 ) is defined as an elevation in IOP of less than 12 to 24 hours' duration. If patients are treated during this phase, vision may be salvageable. Unfortunately, there are often subclinical spikes in IOP before the sustained elevation, which are quite detrimental. Thus, only about 50% of patients regain sight even when treated in the acute phase. 1 Chronic Glaucoma: This type ( FIGURE 4 ) occurs when the IOP elevation is sustained for days or longer. Medical therapy may reduce the IOP, but vision cannot be regained. With time, many of the ocular structures undergo both physiologic and FIGURE 1. Primary glaucoma. The right eye of an 8-year-old female spayed basset hound with primary, chronic glaucoma. Note the episcleral injection, corneal edema, buphthalmos, and lens subluxation (secondary to buphthalmos). The retina appears hyperreflective, with a significant lack of retinal blood vessels (retinal degeneration). FIGURE 2. Secondary glaucoma. The left eye of an 11-year-old male castrated husky with secondary glaucoma. Note the diffuse iris discoloration and focal region of hyphema. TABLE 1 Key Aspects in Comparing Acute and Chronic Glaucoma ASPECT ACUTE GLAUCOMA CHRONIC GLAUCOMA Duration of IOP elevation <12–24 h Days to weeks Globe size Normal Normal to buphthalmic Menace response Usually absent* Absent Direct PLR Usually absent* Absent Indirect PLR Present Absent Dazzle reflex Present Absent Optic nerve/retina Normal to mildly pale optic nerve Cupped, dark optic nerve, regions of tapetal hyperreflectivity, generalized vascular attenuation *Depends on degree of IOP elevation and previous IOP spikes.

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