Angle closure is defined as the apposition of iris to the trabecular meshwork, which results in increased intraocular pressure (IOP). In acute angle closure (AAC), the process occurs suddenly with a dramatic onset of symptoms, including blurred vision, red eye, pain, headache, and nausea and vomiting. The sudden and severe IOP elevation can quickly damage the optic nerve, resulting in acute angle-closure glaucoma (AACG).
AAC is a true ophthalmic emergency, and a delay in treatment can result in blindness. While immediate treatment can sometimes minimize the amount of visual loss, the best treatment is to stop its occurrence in susceptible individuals. [1, 2, 3, 4]
AAC occurs through a process termed pupillary block. Normally, aqueous humor is produced in the ciliary body, flows through the pupil into the anterior chamber, and drains into the trabecular meshwork to exit the eye. When the pupil is mid-dilated, the distance between the iris and the lens is the shortest, and the two structures can come into contact with each other in individuals at risk for angle closure. When this occurs, aqueous humor cannot flow through the pupil into the anterior chamber (pupillary block), pushing the iris forward. When the iris is pushed against the trabecular meshwork, aqueous humor cannot flow out of the eye (angle closure), increasing IOP.
The normal IOP is 10-21 mm Hg. In AAC, and IOP typically exceeds 40 mm Hg. The sudden and severe elevation in IOP can cause irreversible optic nerve damage very quickly (acute angle-closure glaucoma).
Mechanisms other than pupillary block can also contribute to primary angle closure, including plateau iris, use of certain medications, increased iris thickness, increased iris volume with dilation, hyperopia, and increased lens thickness in phacomorphic angle closure.
AAC is more common in older individuals. Among persons older than 40 years, AAC is more common in Inuit and Asian persons, less common in whites, and least common in blacks. While AACG usually accounts for a small proportion of glaucoma cases in the general population, it accounts for significant number of glaucoma cases among persons of Eastern Asian and Southeast Asian descent. It is more common among women and individuals with hyperopia. Individuals with family history of AAC or who have had AAC in one eye are also at a higher risk. [2, 5]
AAC is a medical emergency that needs to be treated immediately. Even with immediate treatment, AAC may result in vision loss. The best method for preventing vision loss due to AAC is prophylactic treatment in patients with susceptible anatomy.
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