Glaucoma is an elevation in intraocular pressure (IOP) with resultant retinal ganglion cell and optic disk damage leading to blindness if uncorrected. Normal intraocular pressure can be anywhere from 10-35 mmHg depending upon the examiner, tonometer,conversion table, breed, age and species. Glaucoma occurs where there is obstruction to the flow of aqueous humor anywhere along the pathway of its normal flow. Aqueous humor is secreted by the epithelium of the ciliary processes into the posterior chamber and reaches the anterior chamber by crossing the pupil. It exits the eye through the pectinate ligament via two different routes. In the conventional route, the aqueous humor passes the ciliary cleft, which contains the trabecular meshwork, and entersthe scleral venous plexus draining either anteriorly via the episcleral and conjunctival veins or posteriorly into the vortex venous system and into the systemic venous circulation (corneoscleral outflow pathway). In the non-conventional route, the aqueous humor drains into the ciliary muscle interstitium to the suprachoroid and diffuses through the sclera (uveoscleral outflow pathway). The balance between these routes is established by the ciliary muscle tone, with more fluid leaving the eye via the uveoscleral pathway when the ciliary muscle is relaxed than when it is contracted. In most species, the majority of the aqueous humor (about 50% in horses, 85% in dogs and 97% in cats) leaves the eye via the conventional outflow route (Slatter). The intraocular pressure rises when the production of aqueous humor exceeds its outflow.
展开▼
