Background
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.
Pathophysiology
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.
Epidemiology
Frequency
United States
Peripheral anterior synechiae occur infrequently.
International
Peripheral anterior synechiae occur infrequently.
Mortality/Morbidity
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.
Race
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.
Sex
Females have shallower anterior chambers; therefore, they may have a greater disposition to formation of PAS.
Age
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.
Tables
General Appearance |
Detailed Appearance |
Possible Causes |
Broad bands |
||
|
PAS to all levels but not to cornea. Bridging usually not present. |
Angle-closure glaucoma |
|
PAS to all levels, sometimes to cornea. Bridging may be present. |
Posterior pushing mechanism, post-operative shallow anterior chamber, or iris bombé |
|
PAS with new vessels, multiple sites |
Neovascularization |
Scattered, irregular |
||
|
PAS tent and form columns up to, but not on, the cornea |
Iridocyclitis with keratic and trabecular precipitates |
|
Small PAS to scleral spur |
Post-argon laser trabeculoplasty |
Iris Pulled Forward |
Iris Pushed Forward |
Neovascular membrane Iridocorneal endothelial membrane Posterior polymorphous dystrophy Epithelial/fibrous ingrowth Uveitis Trauma Inflammatory syndromes Infection Flat anterior chamber Post-surgical Trauma Post-laser trabeculoplasty |
Pupil block Primary angle-closure glaucoma Posterior synechiae resulting in iris bombé Pseudophakic or aphakic pupil block Iridoschisis Plateau iris Choroidal or supraciliary effusion - Posterior uveitis - Central retinal vein occlusion - Nanophthalmos - Post-panretinal photocoagulation or cryotherapy Suprachoroidal hemorrhage Aqueous misdirection syndrome Posterior segment tumors - Retinoblastoma - Choroidal melanoma - Metastasis Iris cyst or tumor Ciliary body cyst or tumor Contracting retrolental tissue - Retinopathy of prematurity - Persistent hyperplastic primary vitreous Post-scleral bucking surgery Anterior lens subluxation (ectopia lentis) Lens intumescence (phacomorphic glaucoma) Neurofibromatosis |
