Peripheral Anterior Synechia

Updated: Jul 26, 2016
  • Author: Andrew J Tatham, MBChB, FRCOphth, FRCSEd, FEBO; Chief Editor: Hampton Roy, Sr, MD  more...
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Overview

Background

Peripheral anterior synechiae (PAS), which were first described by Barkan in 1938, are adhesions between the iris and trabecular meshwork. PAS may reduce outflow of aqueous humor and may lead to raised intraocular pressure.

PAS result from prolonged appositional contact between the iris and trabecular meshwork (as in primary angle closure) or from anterior chamber inflammation or neovascularization (secondary angle closures). PAS may also be associated with anterior segment dysgenesis or other forms of secondary angle closure such as iridocorneal endothelial (ICE) syndrome.

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Pathophysiology

Peripheral anterior synechiae may form under the following 2 circumstances: a nonproliferative state or a proliferative state.

Apposition of the iris against the trabecular meshwork as a result of pupil block or a posterior pushing mechanism without any inflammation can result in continuous peripheral anterior synechiae. These continuous peripheral anterior synechiae lead to "zippering" of the angle. Primary angle-closure glaucoma and the various posterior pushing mechanisms are examples of this process.

In the presence of inflammation or cellular proliferation, a membrane forms between the iris and the trabecular meshwork, creating the peripheral anterior synechiae. This membrane contracts, resulting in angle-closure glaucoma by an anterior pulling mechanism. Examples of this process include the fibrovascular membrane formed in neovascular glaucoma, proliferating abnormal endothelial cells in the iridocorneal endothelial (ICE) syndromes, epithelialization of the angle due to epithelial ingrowth, or inflammatory trabecular and keratic precipitates in contact with an inflamed iris. These processes can be accentuated by iris swelling and protein transudation and exudation.

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Epidemiology

Frequency

United States

Peripheral anterior synechiae occurs infrequently.

International

Peripheral anterior synechiae occurs infrequently.

Mortality/Morbidity

The morbidity of peripheral anterior synechiae lies in its ability to occlude the angle and result in a pathological increase in intraocular pressure.

Race

Asian persons have the highest propensity for primary angle-closure glaucoma and, thus, peripheral anterior synechiae formation. [1] This condition is not as common in blacks. Whites are least likely to develop primary angle-closure glaucoma.

Sex

Females have shallower anterior chambers; therefore, they may have a greater disposition to forming peripheral anterior synechiae.

Age

The risk of peripheral anterior synechiae formation increases with age because of a reduction in anterior chamber depth. This is due to a combination of cataract formation, leading to an increase in the thickness of the lens, and laxity of the zonules, resulting in the forward displacement of the lens.

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