Peripheral Anterior Synechia

Updated: Mar 19, 2021
  • Author: Maria Hannah Pia U de Guzman, MD, DPBO, FPAO; Chief Editor: Hampton Roy, Sr, MD  more...
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Peripheral anterior synechiae (PAS), which were first documented by Salzmann in 1914, [1]  are adhesions between the iris and trabecular meshwork. PAS may reduce outflow of aqueous humor, which leads to elevated intraocular pressure.

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



Peripheral anterior synechiae (PAS) may form in either a nonproliferative 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 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 trabecular meshwork. This membrane contracts, resulting in PAS formation and angle-closure glaucoma caused by an anterior pulling mechanism. Examples of this process include the fibrovascular membrane formed in neovascular glaucoma, proliferating abnormal endothelial cells in iridocorneal endothelial syndromes, epithelialization of the angle due to epithelial ingrowth, and inflammatory trabecular and keratic precipitates in contact with an inflamed iris. These processes can be accentuated by iris swelling and protein transudation and exudation.




United States

Peripheral anterior synechiae occur infrequently.


Peripheral anterior synechiae occur infrequently.


The morbidity of peripheral anterior synechiae (PAS) lies in the ability to occlude the anterior chamber angle, resulting in a pathologic increase in intraocular pressure.


Asian individuals have the highest propensity for primary angle-closure glaucoma and, thus, PAS formation. [2] This condition is not as common in Black individuals. White individuals are least likely to develop primary angle-closure glaucoma.


Females have shallower anterior chambers; therefore, they may have a greater disposition to formation of PAS.


The risk of PAS formation increases with age because of a reduction in anterior chamber depth. This is due to a combination of increased thickness of the lens and laxity of the zonules, resulting in forward displacement of the lens.