Synechiae

A synechia is an eye condition where the iris adheres to either the cornea (i.e.anterior synechia) or lens (i.e. posterior synechia).

It may develop from:-    

                                        

                                        Glaucoma, 

Cataracts, 

Uveitis,

Keratitis or 

As a complication of surgery or trauma to the eye.

Synechiae may prevent or impede the flow of aqueous fluid between the anterior and posterior chambers of the eye, resulting in Angle-closure glaucoma. 

Types of Synechiae:-

1)Anterior synechiae or peripheral anterior synechiae(PAS):-  An adhesion of the iris to the posterior cornea due to abnormal fibrovascular tissue formation.

Peripheral Anterior Synechiae

2) Posterior synechiae:-  An adhesion of the iris to the anterior lens capsule and/or vitreous due to abnormal fibrovascular tissue formation or due to organization of the fibrin rich exudates.

Posterior Synechiae 

3)Concurrent anterior and posterior synechiae.

Peripheral Anterior Synechiae

Pathophysiology:- 

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

Peripheral anterior synechiae may form under the following 2 circumstances: a nonproliferative state 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 peripheral anterior synechiae. These continuous peripheral anterior synechiae 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, creating the peripheral anterior synechiae. This membrane contracts, resulting in angle-closure glaucoma by an anterior pulling mechanism.

 Peripheral anterior synechiae are usually asymptomatic unless large areas of at least 270° of angle are involved. 

Peripheral anterior synechiae are diagnosed on gonioscopic examination.

Description of different types of PAS seen on Gonioscopic examination and their clinical significance:-

Description of PAS	Associations	Possible Conditions
Broad bands
	PAS to all levels but not to cornea No bridging usually present	Angle-closure glaucoma
	PAS to all levels, sometimes to the cornea Bridging may be present	Posterior pushing mechanism, postoperatively shallow AC, or from 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 keratin and trabecular precipitates
	Small PAS to the scleral spur	Post-argon laser trabeculoplasty (ALT)

Treatment of Peripheral anterior synechiae:-

No specific medical management exists pertaining to the treatment of peripheral anterior synechiae (PAS). In general, the treatment of the underlying aetiology prevents the formation of peripheral anterior synechiae.

Types of posterior Synechiae:-

   1)     Segmental:- Segmental posterior synechiae refer to adhesions of iris to lens at some points. In this stage, if mydriatic drops are used the pupil becomes festooned shaped.

    2)   Annular posterior synechiae:- It is the adhesion of the whole rim of the iris to the anterior capsule of the lens (ring synechiae). These prevent the circulation of aqueous humor from the posterior chamber to the anterior chamber (seclusio pupillae). Thus the aqueous collects behind the iris and pushes it anteriorly leading to “iris-bombe” formation. 

   3)  Total:- It is the adhesion of the total posterior surface of the iris to the anterior of the lens. It is rarely formed in the acute plastic type of Uveitis and result in a deepening of the anterior chamber.

Synechiae associated with uveitis have signs like 

• Keratin precipitates, 
• Anterior chamber cells, 
• Flares, 
• Irregular pupils, 
• Ciliary injections, 
• Vitreous cells, 
• Iris abnormalities, 
• Fundal changes as well. 

These signs depend on the type of uveitis anterior, intermediate uveitis, posterior uveitis and panuveitis.

Posterior synechiae are evident on the slit-lamp examination.

Drugs that prevent or increases posterior Synechiae formation:-

Inflammatory states

  o    Topical steroids minimize inflammation and, therefore, peripheral anterior synechiae formation.

  o    Cycloplegics should be used to prevent posterior synechiae. Atropine sulfate also breaks the newly formed synechiae.

  o    Miotics and epinephrine should be avoided because they can increase inflammation.