Glaucoma is a heterogeneous condition that leads to damage of the optic nerve and may result in visual field loss, including complete blindness. Anatomically, glaucoma is classified into open-angle glaucoma and close angle glaucoma. A closed-angle is an anatomical configuration in which there is a mechanical blockage of the trabecular meshwork by the peripheral iris. Etiologically, it can be classified as primary or secondary angle closure. Primary angle-closure is not associated with any other ocular condition, while secondary angle closure is associated with one or more other ocular conditions.
Clinically, angle-closure can be considered acute or chronic. Chronic angle-closure can occur with or without symptoms, and thus it can be described as ''silent" closed-angle glaucoma. Because this condition mainly consists of irido-trabecular contact leading to synechiae formation and subsequent angle closure, it has also been described as "creeping" angle closure.
Peripheral anterior synechiae (PAS) formation between the peripheral iris and trabecular meshwork of the iridocorneal angle is the main etiologic factor in chronic angle closure.
Risk factors for angle-closure include:
In susceptible individuals, some systemic drugs can induce angle-closure:
Glaucoma is the leading cause of irreversible blindness worldwide. Primary open-angle glaucoma is three times more common than angle-closure glaucoma, although angle closure is responsible for 50% of blindness caused by glaucoma. The primary risk factors for angle-closure include older age, female gender, and Asian or Eskimoan race.
Angle-closure impairs aqueous outflow by obstructing, damaging, or degenerating trabecular meshwork, leading to an increase in intraocular pressure and subsequent glaucomatous optic nerve damage. Angle-closure is characterized by the presence of irido-trabecular contact. This contact may lead to chronic closure of the angle due to peripheral anterior synechiae formation. If a glaucomatous optic neuropathy is also present, this is termed chronic angle-closure glaucoma.
The major mechanisms leading to angle closure include:
Chronic angle-closure does not cause symptoms in the majority of patients. Some individuals may present with the following symptoms:
The investigations for angle-closure glaucoma are as under:
Gonioscopy: Indentation gonioscopy is the standard technique used to visualize the angle dynamically to determine the extent of angle-closure due to peripheral anterior synechiae.
Tonometry: Measurement of intraocular pressure. The gold standard is Goldmann applanation.
Pachymetry: Central corneal thickness to adjust intraocular pressure according to corneal thickness.
Slit-lamp examination: Anterior segment examination.
Indirect ophthalmoscopy: Optic nerve head clinical examination.
Perimetry: Visual field analysis.
Optical Coherence Tomography
Ultrasound biomicroscopy: This can assist in evaluating the position of the ciliary body, lens position, and presence of an iridociliary cyst or mass.
A darkroom prone provocation test has been described but is not useful in discriminating primary angle-closure suspects from those with open angles.
Treatment includes the release of pupil block, if present, by means of iridotomy, iridectomy, or lens extraction. If the intraocular pressure cannot be controlled medically after releasing any pupil block, surgery may be required. Because these eyes may be more likely to develop aqueous misdirection, precautions must be considered when undertaking surgery.
Chronic angle-closure glaucoma must also be differentiated from open-angle glaucoma (primary and secondary) as well as causes of nonglaucomatous optic neuropathy such as ischemic, compressive, and hereditary optic neuropathies. Many different etiologies may lead to chronic angle-closure glaucoma (see pathophysiology section above). Determining the mechanism of angle closure is important as treatments may vary depending on the cause of the angle closure.
Primary angle-closure consists of other subtypes which must also be considered in the differential diagnosis:
The prognosis of chronic angle-closure glaucoma is variable and likely depends on many factors such as the stage of disease at detection. A prophylactic peripheral iridotomy does not guarantee prevention of angle-closure glaucoma as over 50% of the fellow eyes may still develop chronic angle-closure glaucoma over time despite receiving a peripheral iridotomy at the time of an attack of angle-closure in the contralateral eye.
More extensive peripheral anterior synechiae and narrower width of the drainage angle are associated with higher intraocular pressure and a larger vertical cup-to-disc ratio. Higher mean intraocular pressure and history of acute angle-closure are associated with poorer visual field and acuity outcomes with 7% progressing to blindness while on treatment over a ten year period in a Chinese population.
Glaucomatous damage to the optic nerve may lead to visual field loss, decreased visual acuity, and complete blindness. Damage to the corneal endothelium may occur, leading to corneal decompensation. Blind eyes with end-stage glaucoma may also become phthisical. Aqueous misdirection syndrome may develop more frequently following surgery in eyes with chronic angle-closure glaucoma.
Patients with severe vision loss may benefit from an evaluation with a low vision specialist who may help them maximize their remaining vison when performing visual activities.
Glaucoma may develop and cause visual field loss without any symptoms. For this reason, early detection is vital to the prevention of loss of vision. Patients with narrow or occludable angles should have regular exams with gonioscopy and intraocular pressure measurement to monitor for the development of angle closure. In addition, they should be educated regarding the symptoms of acute angle-closure.
A prophylactic laser peripheral iridotomy may reduce the risk of development of acute angle-closure for high-risk populations but does not eliminate the risk of acute angle-closure. Intraocular pressure alone is inadequate to screen for or diagnose glaucoma . Patients at risk should be aware that some medications may precipitate angle closure.
All healthcare team members should be aware of the symptoms of acute angle-closure, as acute episodes may precede chronic angle closure. These symptoms include hazy or blurry vision, particularly if accompanied by nausea, eye pain, or headache. Eye care providers should screen patients for angle-closure risk during routine eye exams to identify patients at higher risk and refer them to a subspecialist if necessary. General practitioners should refer patients with suspected symptoms of angle-closure to an eye care provider for evaluation. Pharmacists should be aware of medications that could precipitate angle closure and educate patients or refer them to an eye care provider if necessary.
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