Peripheral Anterior Synechiae - Causes, Symptoms, Diagnosis, and Treatment

What Is Peripheral Anterior Synechiae?

Peripheral anterior synechiae (PAS) is one of the pathognomonic signs of angle-closure glaucoma. Synechiae are defined as adhesions that are present in the eyes. Synechiae are present either anteriorly or posteriorly. When synechiae are formed between the iris and anterior lens capsule, it is known as posterior synechiae. When there is the adhesion of the iris to the anterior iridocorneal angle, it is known as PAS.

What Are the Major Causative Factors of PAS?

PAS is caused primarily because of persistent inflammatory or infectious conditions. Prolonged states of inflammation and infective causes associated with PAS include:

• Inflammatory conditions (uveitis, iridocyclitis, interstitial keratitis, lens-related uveitis, sarcoidosis).

• Infections (herpes simplex, herpes zoster, tuberculosis, and syphilis).

• Other causes for the formation of PAS comprise:

  • Trauma.

  • Increased intraocular pressure.

  • Aniridia (eye disorder characterized by complete or partial absence of the iris)

  • Other developmental abnormalities.

  • The complication of ocular surgery (anterior flat chamber surgery).

What Is the Principal Mechanism Involved Behind the Formation of PAS?

The exact mechanism which initiates the formation of PAS is not known. Several theories describing the development of PAS have been postulated.

The most accepted ideas related to the development of PAS are:

1. Adherence of the peripheral iris to the Schwalbe's line and the attachment extends outwardly towards the angle recess.

2. The peripheral iris first attaches to the angle recess and then extends towards Schwalbe's line.

The development of PAS occurs in a state of proliferative or non-proliferative phase linked to the underlying inflammatory condition. Repeated apposition of proteins, inflammatory cells, and fibrin leads to the attachment of the iris to the trabecular meshwork.

What Are the Different Factors That Control the Extension of PAS?

The several factors that contribute to the formation as well the extension of PAS are:

• Visual field damage.

• More prominent vertical cusp-to-disc ratio.

• Higher untreated intraocular pressure.

• The iris's physical characteristics comprise thickness, contour, and adhesiveness.

What Are the Signs and Symptoms to Watch Out for in Patients Suffering From PAS?

PAS, by and large, remains asymptomatic. It typically presents signs and symptoms of inflammation related to the underlying cause, like photophobia, decreased vision, and redness. If left untreated, it is followed by angle-closure glaucoma.

The intensity of the disease condition depends on the chronicity of the state.

Clinically it is present in three forms:

• Acute angle closure manifests itself with symptoms of acute angle glaucoma accompanied by headache, eye pain, nausea, halos, and blurred visions.

• Subacute cases report intermittent mild attacks of acute angle-closure glaucoma.

• Chronic angle closure is presented by vision loss due to glaucoma caused by optic neuropathy.

How Is the Diagnosis of PAS Performed?

Forming a confirmatory PAS diagnosis involves a clinical examination and eye field imaging.

• Clinical examination of the eye affected by PAS is done by slit lamp technique and gonioscopy.

• Gonioscopy is ideal for physically examining PAS's angle structures and pupillary margins.

• The full extent of the PAS is visualized using imaging techniques like ultrasound biomicroscopy (a high-resolution non-invasive technique that helps visualize anterior segment structures of the eye in detail). Corneal specular microscopy (helps assess the corneum's endothelial morphologic attribute).

What Are the Ocular Conditions That Show Similarity to PAS?

The conditions that are similar to PAS are:

• Central retinal vein occlusion is an ocular condition where the main vein draining blood from the retina closes off, leading to blurred vision.

• Choroidal detachment is the detachment of the choroid from the sclera causing increased intraocular pressure and reduced vision.

• Choroidal melanoma is the second most common tumor affecting the eye. It is described as blurred vision as one of its symptoms.

• Hyphema glaucoma occurs secondary to hyphema resulting in angle recession and shearing of the iris.

What Are the Different Treatment Approaches Used In Treating PAS?

There is no specific strategy for managing PAS. The ultimate goal of the treatment is to decrease the intraocular pressure and prevent further closure of the angle. A few measures used for treating PAS are:

• Removal of the underlying cause.

• Anti-glaucoma drugs like beta-blockers, topical alpha-agonists, and prostaglandin analogs are prescribed to decrease intraocular pressure.

• Short-acting cycloplegics are administered to prevent posterior synechiae formation.

• Topical corticosteroids are administered to suppress inflammation.

• Peripheral iridotomy with laser is advised for patients suffering from angle closure.

• Steroids, miotics, and Epinephrine are avoided in patients with uveitis as they increase the risk of worsening the inflammation and forming posterior synechiae.

• Severe cases warrant surgical management of the PAS -

  • Iridotomy (surgical technique of creating a hole in the iris to relieve pupillary obstruction)

  • Surgical goniosynechialysis the physical removal of the PAS to enable the flow of aqueous fluid and thus decrease the intraocular pressure.

What Are the Most Common Complications Arising in Patients With PAS?

Untreated PAS often culminates in furthering myriad eye complications, ultimately resulting in vision loss. The difficulties associated with PAS are:

• Secondary angle-closure glaucoma is an eye condition secondary to the eye's angle (angle formed between the iris and cornea) block.

• The blockage due to synechia mainly causes increased intraocular pressure in the eye.

• Blurred vision is the loss of sharp focus of the objects by the eyes, thus rendering the thing hazy.

• Glaucomatous neuropathy is the progressive loss of the retinal ganglion cells, leading to organizational and functional damage to the optic nerve. It clinically manifests as blurred vision and blindness.

What Is the Final Outlook of PAS?

The overall outlook of PAS is good, with complete remission of the condition possible after immediate post-treatment. Cases with persistent untreated PAS are more vulnerable to secondary angle glaucoma.

Conclusion:

PAS is a rare disorder of the eye that often remains undiagnosed initially. Appropriate therapeutic measures at an early stage resolve the lesion and prevent further complications.