Excerpt from Synechia, Peripheral Anterior

Synonyms, Key Words, and Related Terms: peripheral anterior synechia, peripheral anterior synechiae, PAS, intraocular pressure, IOP, anterior chamber, angle-closure glaucoma, peripheral iris, trabecular meshwork

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Background: Since the early 1900s, the status of the angle has been recognized as highly relevant in the analysis of glaucoma. In 1938, Barkan described peripheral anterior synechiae (PAS) between the peripheral iris and trabecular meshwork (TM), which could lead to increased intraocular pressure (IOP). In 1952, Chandler recognized that narrowing of the angle would decrease outflow, thereby increasing ocular tension.

Today, PAS are a well-recognized consequence of altered anterior chamber (AC) anatomy and AC inflammation. PAS subsequently can result in significant morbidity as a precipitant to secondary angle-closure glaucoma.

Pathophysiology: PAS may form under the following 2 circumstances: a nonproliferative state or a proliferative state.

Apposition of the iris against the TM as a result of pupil block or a posterior pushing mechanism without any inflammation can result in continuous PAS. These continuous PAS 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 TM, creating the PAS. 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

Frequency:

In the US: Infrequent

Internationally: Infrequent

Mortality/Morbidity: The morbidity of PAS lies in its ability to occlude the angle and result in a pathological increase in IOP.

Race: Asians have the highest propensity for primary angle-closure glaucoma and, thus, PAS formation. This condition is not as common in blacks. Whites are least likely to develop primary angle-closure glaucoma.

Sex: Females have shallower ACs; therefore, they may have a greater disposition to forming PAS.

Age: The risk of PAS formation increases with age because of a reduction in AC 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.