Peripheral Anterior Synechia

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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.

History

Peripheral anterior synechiae (PAS) can present in the following ways:

The history can be valuable in identifying the process or processes that may have led to PAS formation. Specific inquiry should include the following:

Physical

Both eyes should be examined. Examination of the unaffected eye in unilateral presentations can be extremely helpful in determining the etiology of PAS formation.

The following aspects of the clinical ophthalmic examination are relevant.

Table 1. Appearance of Peripheral Anterior Synechiae (PAS) on Gonioscopy



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See Table

The following aspects of the clinical ophthalmic examination are relevant. 

Causes

Table 2. Summary of Important Causes of Peripheral Anterior Synechiae by Mechanism



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See Table

The causes of peripheral anterior synechiae (PAS) are as follows:

Approach Considerations

The appropriate management of peripheral anterior synechiae (PAS) depends on the disease process that has led to the formation of the PAS. 

Laboratory Studies

Perform an inflammatory and/or infectious workup as required.

Imaging Studies

Ultrasound biomicroscopy[6] or anterior segment imaging (eg, optical coherence tomography[7] )

Corneal specular microscopy - useful in identifying iridocorneal endothelial or posterior polymorphous dystrophy cells

Other Tests

Provocative testing - measures intraocular pressure while dilating or constricting the pupil to differentiate angle-closure glaucoma from open-angle glaucoma with narrow angles. However, it correctly identifies only 50%-70% of patients with true angle-closure glaucoma.

Procedures

A paracentesis with injection of viscoelastic into the anterior chamber done in an attempt to deepen a narrow angle can be used to differentiate appositional closure from synechial closure. By deepening the angle, a better view of the angle can be obtained to determine the presence of PAS. Sometimes, this procedure can be both diagnostic and therapeutic.

Histologic Findings

Histologic findings depend on the causative agent; they can be fibrovascular, epithelial, endothelial, or inflammatory in nature.

Staging

No formal staging scale exists.

Approach Considerations

The appropriate management of peripheral anterior synechiae (PAS) depends on the disease process that leads to the formation of the PAS. 

Medical Care

The following drug categories may be considered, depending on the primary diagnosis: topical β-blockers, topical α-agonists, topical carbonic anhydrase inhibitors, oral carbonic anhydrase inhibitors, topical prostaglandin agonists, miotics, cycloplegics, and topical corticosteroids.

Treat elevated intraocular pressure, as necessary.

Treat inflammation, as necessary.

Surgical Care

General principles in the surgical treatment of peripheral anterior synechiae (PAS) are as follows:

Consultations

A rheumatologic consultation should be considered in patients with a sterile uveitis of unknown origin.

Long-Term Monitoring

Long-term monitoring depends on the etiology of the peripheral anterior synechiae and the severity or stage of the condition.

Medication Summary

No specific medication that can treat peripheral anterior synechiae (PAS) is available. Some medications may act on the underlying etiology to prevent the formation or progression of PAS. Most medications are only capable of treating the main sequela of PAS, which is elevation of intraocular pressure (IOP).

Brimonidine (Alphagan)

Clinical Context:  Selective alpha2-receptor that reduces aqueous humor formation and increases uveoscleral outflow.

Apraclonidine (Iopidine)

Clinical Context:  Reduces intraocular pressure. A relatively selective alpha-adrenergic agonist that does not have significant local anesthetic activity. Has minimal cardiovascular effects.

Class Summary

Topical adrenergic agonists, or sympathomimetics, decrease aqueous production and reduce resistance to aqueous outflow. Adverse effects include dry mouth and allergic reactions.

Levobunolol (AKBeta, Betagan)

Clinical Context:  Nonselective beta-adrenergic blocking agent that lowers IOP by reducing aqueous humor production and possibly increases outflow of aqueous humor.

Betaxolol ophthalmic (Betoptic, Betoptic S)

Clinical Context:  Selectively blocks beta1-adrenergic receptors with little or no effect on beta2-receptors. Reduces IOP by reducing production of aqueous humor.

Timolol maleate (Timoptic, Timoptic XE, Blocadren)

Clinical Context:  May reduce elevated and normal IOP, with or without glaucoma, by reducing production of aqueous humor or by outflow.

Class Summary

Topical beta-adrenergic receptor antagonists decrease aqueous humor production by the ciliary body. Adverse effects of beta-blockers are due to systemic absorption of the drug and include decreased cardiac output and bronchial constriction. In susceptible patients, this may cause bronchospasm, bradycardia, heart block, or hypotension. Pulse rate and blood pressure should be monitored in patients receiving topical beta-blocker therapy, and punctal occlusion may need to be performed after administration of the drops.

Pilocarpine (Akarpine, Adsorbocarpine, Ocusert Pilo-40, Pilagan, Pilocar)

Clinical Context:  Directly stimulates cholinergic receptors in the eye, decreasing resistance to aqueous humor outflow.

Instillation frequency and concentration are determined by patients' response. Individuals with heavily pigmented irides may require higher strengths.

If other glaucoma medications also are being used, at bedtime, use gtt at least 5 min before gel.

Patients may be maintained on pilocarpine as long as IOP is controlled and there is no deterioration in visual fields. May use alone or in combination with other miotics, beta-adrenergic blocking agents, epinephrine, carbonic anhydrase inhibitors, or hyperosmotic agents to decrease IOP.

Class Summary

Causes contraction of the ciliary muscle which tightens the trabecular meshwork and allows increased outflow of aqueous. Miosis results from action of these drugs on the pupillary sphincter. Adverse effects include brow ache, induced myopia, and decreased vision in low light.

Latanoprost (Xalatan, Xelpros)

Clinical Context: 

Tafluprost (Zioptan)

Clinical Context: 

Travoprost ophthalmic (Travatan, Travatan Z)

Clinical Context: 

Bimatoprost (Latisse, Lumigan)

Clinical Context: 

Latanoprostene bunod ophthalmic (Vyzulta)

Clinical Context: 

Class Summary

Increase uveoscleral outflow of aqueous humor. One mechanism of action may be through induction of metalloproteinases in ciliary body, which breaks down extracellular matrix, thereby reducing resistance to outflow through the ciliary body.

Atropine IV/IM (Atropisol, Atropair, Isopto)

Clinical Context:  Acts at parasympathetic sites in smooth muscle to block response of sphincter muscle of iris and muscle of ciliary body to acetylcholine, causing mydriasis and cycloplegia. Phenylephrine (2.5% or 10% solution) concurrently with atropine may prevent formation of synechiae by producing wide dilation of pupil.

Class Summary

Causes pupil dilation which may help break or prevent posterior synechiae formation. Causes relaxation of the ciliary muscle which can deepen the anterior chamber.

Acetazolamide (Diamox, Diamox Sequels)

Clinical Context:  Inhibits enzyme carbonic anhydrase, reducing rate of aqueous humor formation which, in turn, reduces IOP. Used for adjunctive treatment of chronic simple (open-angle) glaucoma and secondary glaucoma and preoperatively in acute angle-closure glaucoma when there is a delay of the surgery intended to lower the IOP.

Methazolamide (Neptazane)

Clinical Context:  Reduces aqueous humor formation by inhibiting enzyme carbonic anhydrase, which results in decreased IOP.

Dorzolamide (Trusopt, Cosopt)

Clinical Context:  Used concomitantly with other topical ophthalmic drug products to lower IOP. If more than one ophthalmic drug is being used, administer the drugs at least 10 min apart. Reversibly inhibits carbonic anhydrase, reducing hydrogen ion secretion at renal tubule and increasing renal excretion of sodium, potassium bicarbonate, and water to decrease production of aqueous humor.

Brinzolamide (Azopt)

Clinical Context:  Catalyzes reversible reaction involving hydration of carbon dioxide and dehydration of carbonic acid. May use concomitantly with other topical ophthalmic drug products to lower IOP. If more than one topical ophthalmic drug is being used, administer drugs at least 10 min apart.

Class Summary

Reduce secretion of aqueous humor by inhibiting carbonic anhydrase in the ciliary body. In acute angle-closure glaucoma, carbonic anhydrase inhibitors may be given systemically, but they are used topically in refractory open-angle glaucoma patients. Topical formulations are less effective, and their duration of action is shorter than many other classes of drugs. Adverse effects of topical carbonic anhydrase inhibitors are relatively rare, but they include superficial punctate keratitis, acidosis, paresthesias, nausea, depression, and lassitude.

Netarsudil ophthalmic (Rhopressa)

Clinical Context:  Thought to lower intraocular pressure by increasing outflow through the trabecular meshwork.

Further Outpatient Care

Further care depends on the disease process that leads to peripheral anterior synechiae (PAS) formation.

Deterrence/Prevention

Appropriate and timely management of the disease process that can lead to PAS is necessary to prevent PAS from forming or progressing. This is the most important aspect of management because once PAS have formed treatment shifts to managing the sequela of PAS, intraocular pressure elevation, rather than the PAS itself.

Complications

Complications include elevated intraocular pressure leading to ocular pain, decreased visual acuity, and glaucomatous optic neuropathy with vision loss.

Prognosis

Peripheral anterior synechiae should be treated within 6 months of formation if the trabecular meshwork is to regain normal function[8] . Beyond this, the trabecular meshwork will have sustained permanent damage.

Ultimately, prognosis depends on the adequacy of management of the etiologic process that led to PAS formation.

Eyes with 360 degrees of PAS are unlikely to be treated adequately with medications and are likely to require a glaucoma filtering procedure.

Patient Education

Patient education depends on the disease process that led to PAS formation. Emphasis must be placed on the necessity of prompt treatment to prevent the progression of the condition.

What is peripheral anterior synechiae (PAS)?What is the pathophysiology of peripheral anterior synechiae (PAS)?What is the prevalence of peripheral anterior synechiae (PAS)?What is the morbidity and mortality associated with peripheral anterior synechiae (PAS)?What are the racial predilections for peripheral anterior synechiae (PAS)?Why are women at higher risk for peripheral anterior synechiae (PAS)?How does age impact the risk for peripheral anterior synechiae (PAS)?Which clinical history findings are characteristic of peripheral anterior synechiae (PAS)?What is the focus of the clinical history for the evaluation of peripheral anterior synechiae (PAS)?Which physical findings are characteristic of peripheral anterior synechiae (PAS)?What causes peripheral anterior synechiae (PAS)?What are the differential diagnoses for Peripheral Anterior Synechia?Which factors determine the treatment of peripheral anterior synechiae (PAS)?Which lab tests are performed in the workup of peripheral anterior synechiae (PAS)?What is the role of imaging studies in the workup of peripheral anterior synechiae (PAS)?What is the role of provocative testing in the workup of peripheral anterior synechiae (PAS)?What is the role of paracentesis in the workup of peripheral anterior synechiae (PAS)?Which histologic findings are characteristic of peripheral anterior synechiae (PAS)?How is peripheral anterior synechiae (PAS) staged?How is peripheral anterior synechiae (PAS) treated?What is the role of medications in the treatment of peripheral anterior synechiae (PAS)?What is the role of surgery in the treatment of peripheral anterior synechiae (PAS)?Which specialist consultations are beneficial to patients with peripheral anterior synechiae (PAS)?What is included in the long-term monitoring of peripheral anterior synechiae (PAS)?Which medications are used in the treatment of peripheral anterior synechiae (PAS)?Which medications in the drug class Ophthalmics, Other are used in the treatment of Peripheral Anterior Synechia?Which medications in the drug class Carbonic anhydrase inhibitors are used in the treatment of Peripheral Anterior Synechia?Which medications in the drug class Cycloplegics/mydriatics are used in the treatment of Peripheral Anterior Synechia?Which medications in the drug class Antiglaucoma, Prostaglandin Agonists are used in the treatment of Peripheral Anterior Synechia?Which medications in the drug class Miotic agents (parasympathomimetics) are used in the treatment of Peripheral Anterior Synechia?Which medications in the drug class Beta-blockers are used in the treatment of Peripheral Anterior Synechia?Which medications in the drug class Adrenergic agonists are used in the treatment of Peripheral Anterior Synechia?Which factors determine the long-term care for patients with peripheral anterior synechiae (PAS)?How is the progression of peripheral anterior synechiae (PAS) prevented?What are the possible complications of peripheral anterior synechiae (PAS)?What is the prognosis for peripheral anterior synechiae (PAS)?What is included in the patient education about peripheral anterior synechiae (PAS)?

Author

Maria Hannah Pia U de Guzman, MD, DPBO, FPAO, Consultant, Department of Ophthalmology, Glaucoma Section, Asian Hospital and Medical Center; Consultant, Eye Institute, Glaucoma Service, St Luke’s Medical Center, Philippines

Disclosure: Nothing to disclose.

Specialty Editors

Simon K Law, MD, PharmD, Clinical Professor of Health Sciences, Department of Ophthalmology, Jules Stein Eye Institute, University of California, Los Angeles, David Geffen School of Medicine

Disclosure: Nothing to disclose.

J James Rowsey, MD, Former Director of Corneal Services, St Luke's Cataract and Laser Institute

Disclosure: Nothing to disclose.

Chief Editor

Hampton Roy, Sr, MD, † Associate Clinical Professor, Department of Ophthalmology, University of Arkansas for Medical Sciences

Disclosure: Nothing to disclose.

Additional Contributors

Andrew J Tatham, MD, MBA, FRCOphth, FEBO, FRCS(Ed), Consultant Ophthalmic Surgeon, Princess Alexandra Eye Pavilion; Honorary Senior Clinical Lecturer, University of Edinburgh; NHS Scotland Career Research Fellow

Disclosure: Serve(d) as a director, officer, partner, employee, advisor, consultant or trustee for: Allergan; Santen; Thea; Glaukos<br/>Serve(d) as a speaker or a member of a speakers bureau for: Allergan; Heidelberg Engineering; Alcon; Santen.

Baseer U Khan, MD, Associate Professor of Ophthalmology, University of Toronto Faculty of Medicine; Ophthalmologist, Clarity Eye Institute, Canada

Disclosure: Nothing to disclose.

Bradford Shingleton, MD, Assistant Clinical Professor of Ophthalmology, Harvard Medical School; Consulting Staff, Department of Ophthalmology, Massachusetts Eye and Ear Infirmary

Disclosure: Nothing to disclose.

Iqbal Ike K Ahmed, MD, FRCSC, Clinical Assistant Professor, Department of Ophthalmology, University of Utah

Disclosure: Nothing to disclose.

Khalid Hasanee, MD, Glaucoma and Anterior Segment Fellow, Department of Ophthalmology, University of Toronto

Disclosure: Nothing to disclose.

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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 sitesNeovascularization
Scattered, irregular
 PAS tent and form columns up to, but not on, the corneaIridocyclitis with keratic and trabecular precipitates
 Small PAS to scleral spurPost-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