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What Are Posterior Synechiae?

Posterior synechiae are adhesions between the back surface of the iris and the anterior lens capsule, most often caused by inflammation in the anterior chamber. Fibrin and inflammatory cells make the iris stick to the lens at the pupillary margin. These adhesions can be focal or circumferential. When extensive, they prevent the pupil from dilating or constricting normally and can block aqueous flow, contributing to pupil block and angle closure. Posterior synechiae are a common consequence of untreated or recurrent uveitis.

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What Are Posterior Synechiae?

Posterior synechiae are adhesions between the back surface of the iris and the anterior lens capsule, most often caused by inflammation in the anterior chamber. Fibrin and inflammatory cells make the iris stick to the lens at the pupillary margin. These adhesions can be focal or circumferential. When extensive, they prevent the pupil from dilating or constricting normally and can block aqueous flow, contributing to pupil block and angle closure. Posterior synechiae are a common consequence of untreated or recurrent uveitis.

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How Posterior Synechiae Form

During episodes of anterior uveitis, protein and fibrin leak into the aqueous humor, and the inflamed iris becomes more prone to sticking to nearby structures. When the pupil is relatively small, the iris is in close contact with the lens capsule, and fibrin bridges can form. If these connections are not broken early with pharmacologic dilation, they organize into firm adhesions. Repeated inflammation strengthens and extends the synechiae. Over time, a ring of attachment called seclusio pupillae can develop.

Clinical Effects and Complications

Posterior synechiae can cause an irregular, distorted pupil that moves poorly with light or dilating drops. When adhesions are sectoral, the pupil may become peaked or teardrop shaped toward the area of attachment. Complete 360 degree adhesions trap aqueous in the posterior chamber, increasing pressure behind the iris and promoting iris bombe and secondary angle closure. Synechiae also complicate cataract surgery by limiting dilation and increasing the chance of iris trauma. Early recognition allows more effective prevention of these issues.

Diagnosis and Examination

Diagnosis is made by slit lamp examination, which shows areas where the pupillary margin sticks to the lens and fails to separate with usual dilation. Transillumination and careful observation of the pupil shape and movement help locate adhesions. Signs of current or past uveitis, such as keratic precipitates or anterior chamber cells, are often present. Intraocular pressure measurement and gonioscopy assess any secondary angle changes. Documentation with photographs can be useful for monitoring over time.

Prevention, Treatment, and Prognosis

Prevention focuses on prompt and adequate treatment of uveitis with anti inflammatory drops and cycloplegic agents that keep the pupil mobile. When fresh synechiae are present, strong mydriatics can sometimes break them mechanically. Long standing adhesions are often resistant and may require surgical synechiolysis during cataract or glaucoma surgery. Prognosis depends on the extent of adhesions and associated complications. Good control of inflammation reduces new synechiae formation and supports better visual outcomes.

FAQs About Posterior Synechiae

Can posterior synechiae go away on their own?

Very fresh adhesions can separate with dilation, but established synechiae usually persist without surgical intervention.

Do posterior synechiae always cause glaucoma?

Not always, but extensive adhesions that block aqueous flow increase the risk of secondary angle closure and pressure elevation.

Will I always need strong dilating drops if I have synechiae?

Cycloplegic and mydriatic drops are most important during active uveitis to prevent new adhesions and break fresh ones.

Can cataract surgery fix posterior synechiae?

Surgery can release adhesions and improve pupil shape, but careful technique is needed, and underlying inflammation must be well controlled.

References

Vagelos College of Physicians and Surgeons, Columbia University. ?Anterior Uveitis.? https://www.vagelos.columbia.edu/departments-centers/ophthalmology/education/digital-reference-ophthalmology/cornea-and-external-diseases/non-infectious/anterior-uveitis

EyeWiki. ?Synechiae.? https://eyewiki.org/Synechiae

NCBI Bookshelf (StatPearls). ?Iritis.? https://www.ncbi.nlm.nih.gov/books/NBK430909/

MSD Manual Professional Version. ?Overview of Uveitis.? https://www.msdmanuals.com/professional/eye-disorders/uveitis-and-related-disorders/overview-of-uveitis

Cleveland Clinic. ?Uveitis: Symptoms, Causes, Treatment & Types.? https://my.clevelandclinic.org/health/diseases/14414-uveitis