Parul Ichhpujani

BASICS

DESCRIPTION

• “Statistical” hypotony can be defined as an intraocular pressure (IOP) less than 6.5 mm Hg, which corresponds to more than 3 standard deviations below the mean.

• “Clinically significant” hypotony represents the condition where the IOP is low enough to result in visual loss.

EPIDEMIOLOGY

Incidence

• Transient hypotony: Common following glaucoma surgery, surgeries involving a pars plana approach, or following trauma. The rate of hypotony following uncomplicated cataract surgery is extremely low. The incidence of hypotony following trabeculectomy increases with the use of antifibrotic agents such as Mitomycin-C.

• Chronic hypotony: Hypotony leading to phthisis is rare and occurs only in eyes with severe damage.

RISK FACTORS

• Young, male, myopes (low scleral rigidity).

• Uveitis.

GENERAL PREVENTION

• Hypotony following glaucoma surgery can be prevented in several ways.

– Exposure time and the concentration of antimetabolites can be reduced, if used.

– Using releasable sutures or placing extra sutures in the trabeculectomy flap may prevent overfiltration.

– For tube shunts, choosing a valved device or modifying the shunt with a ligature suture can slow drainage.

– Leave the anterior chamber inflated with viscoelastic at the end of the case.

– Aggressive use of anti-inflammatory agents can help prevent the cycle of iridocyclitis and hypotony.

PATHOPHYSIOLOGY

• Hypotony occurs when aqueous humor production does not keep pace with outflow.

• Impaired outflow: Outflow may be greater than usual, as seen with wound leak, overfiltering bleb, or cyclodialysis cleft.

• Impaired production: Conditions that alter ciliary body function, such as iridocyclitis, tractional detachment, or hypoperfusion.

• Role of inflammation: It causes increased permeability of the blood–aqueous barrier.

• Altered equation of conventional and uveoscleral outflow: Flow through the conventional route ceases when IOP declines below the episcleral venous pressure, usually 9 mm Hg. Therefore, uveoscleral outflow predominates at low IOPs.

• Choroidal fluid is believed to accumulate as a result of enhanced uveoscleral outflow and decreased aqueous humor production, a cycle that is often perpetuated once choroidal effusions develop. A ring of anterior choroidal fluid can cause forward rotation of the ciliary body, impairing aqueous humor production.

ETIOLOGY

• Unilateral hypotony is seen with the following:

– Wound leak

– Overfiltering or inadvertent bleb

– Cyclodialysis cleft

– Inflammation—Iridocyclitis or trauma

– Retinal detachment

– Ocular ischemia

– Scleral perforation with needle or suture, or scleral rupture following trauma

– Chemical cyclodestruction from antimetabolites

– Photocoagulation or cryoablation of the ciliary body

– Pharmacologic aqueous humor suppression

• Bilateral hypotony is seen with the following:

– Systemic hypertonicity or acidosis—dehydration, uremia, uncontrolled diabetes, or use of hyperosmotic agents

– Myotonic dystrophy

COMMONLY ASSOCIATED CONDITIONS

Direct trauma with undiagnosed eye wall perforation.

DIAGNOSIS

HISTORY

• Recent trauma or surgery, especially primary glaucoma surgery with antimetabolites

• Blurred vision

• Eye pain (usually a deep ache), especially with choroidal detachment (hemorrhagic choroidal detachment can cause extreme pain)

• History of eye inflammation or systemic illnesses predisposing to uveitis

• Signs and symptoms associated with retinal detachment

PHYSICAL EXAM

• Seidel positive wound leak

• Large bleb following trabeculectomy or tube shunt

• Shallowing of the anterior chamber

• Corneal edema and decompensation

• Synechiae formation

• Corneal astigmatism

• Inflammatory cells and flare in the anterior chamber

• Accelerated cataract formation

• Cyclodialysis cleft

• Ciliochoroidal detachment—serous or hemorrhagic

• Hypotony maculopathy

• Retinal folds

• Vascular engorgement and tortuosity

• Optic disc swelling

• Retinal detachment

DIAGNOSTIC TESTS & INTERPRETATION

Lab

Initial lab tests

• Hypotony is usually diagnosed based on only the history and the physical examination.

• In patients with undiagnosed but suspected uveitis, evaluate for systemic inflammatory disease, especially if the condition is recurrent

• In patients with bilateral hypotony, test for glucose, BUN, and creatinine

Imaging

Initial approach

• B-scan ultrasonography: Useful when the fundus is not easily visualized. It can help in determining the size and the extent of ciliochoroidal detachment, choroidal hemorrhage, and retinal detachment.

• Ultrasonic biomicroscopy or anterior optical coherence tomography (ASOCT): These can help to further evaluate the anterior chamber depth, the position of the ciliary body, and the presence of anterior ciliary detachment or cyclodialysis cleft.

• OCT: OCT scan of the posterior pole can help to better demonstrate subtle macular fluid or folds.

Follow-up & special considerations

• OCT to see resolution of macular fluid and folds of the choroid

• Close and frequent follow-up for uveitic patients and diabetics

Diagnostic Procedures/Other

Fluorescein angiography is helpful in demonstrating the chorioretinal folds, which in relatively mild degrees may be overlooked.

Pathological Findings

• Corneal changes

• Accelerated cataract formation

• Choroidal fluid

• Choroidal folds

• Maculopathy with disturbance of the retinal pigment epithelium (RPE)

• Cystoid macular edema

• Optic disc edema

DIFFERENTIAL DIAGNOSIS

• Idiopathic chorioretinal folds

• Choroidal detachment

• Postoperative endophthalmitis

• Scleral inflammation

• Uveitic glaucoma

• Hyphema

• Corneoscleral laceration

• Postoperative retinal detachment

• Rhegmatogenous retinal detachment

• Tractional retinal detachment

• Uveitis

TREATMENT

MEDICATION

First Line

• Hypotony is best managed by correcting the underlying problem. The anterior chamber may be reformed with viscoelastic as a temporizing measure.

• Steroids may improve aqueous humor production by decreasing ciliary body inflammation.

• Atropine and other cycloplegics deepen the anterior chamber to lessen iris–corneal touch.

Second Line

• Drainage of the choroidal detachment.

• Tighten the sclera flap with additional sutures or revise the trabeculectomy.

• Tie off the tube shunt with a permanent or dissolving suture.

• Large bandage contact lens for seidel positive leak in the bleb or at the limbus

• Patching after atropine

• Systemic medications for treatment of iridocyclitis

• Repair cyclodialysis cleft if present.

ADDITIONAL TREATMENT

General Measures

• The patient should avoid lifting, bending, and strenuous activity. Sudden movement or straining could cause a vessel, which already is stretched in the suprachoroidal space, to bleed and create a suprachoroidal hemorrhage.

• The patient should avoid any direct pressure on the eye that could cause further decompression.

• An eye shield at bedtime is advisable.

Issues for Referral

• Unresolved macula folds

• Persistent wound leak

• Cyclodialysis repair

• Kissing choroidals

• Flat chamber with touch of the iris to the edge of the pupil or involving the pupil with corneal folds and decompensation

Additional Therapies

• Nonsteroidal medications topically and orally to decrease inflammation and avoid papillary membrane formation

• Immediate reformation of the anterior chamber with viscoelastic if the chamber is flat and involving the pupil or if there is corneal decompensation

COMPLEMENTARY & ALTERNATIVE THERAPIES

• Encourage oral hydration.

• Laxatives and avoid Valsalva to decrease the chance of a suprachoroidal hemorrhage when the eye is hypotonus.

SURGERY/OTHER PROCEDURES

• Treatment of wound leaks:

• Small wound leaks with a well-formed anterior chamber: Conservative management with patching or a large diameter bandage contact lens

• Focal leak: Cyanoacrylate glue application with a contact lens placed over the glue

• Large wound leaks causing clinically significant hypotony: Surgical revision using a round bodied needle to prevent leaks from suture tracts

• Cyclodialysis cleft: Treatment options include argon laser photocoagulation, cryotherapy, and ciliary body suturing.

• Conjunctival flaps can work well for diffusely incompetent blebs due to tissue thinning and avascularity.

• For chronic hypotony, surgical wound revision with resuturing of the flap, and/or conjunctival advancement or autograft is the procedure of choice.

• Treatment of uveitis:

• Anti-inflammatory agents are the mainstay of treatment. Intravitreal steroid injections can be tried in prephthisical eyes.

• Surgical removal of a cyclitic membrane may release tractional detachment of the ciliary body.

• Vitrectomy and placement of silicone oil may be useful in refractory cases.

IN-PATIENT CONSIDERATIONS

This condition can be monitored and treated as an outpatient.

ONGOING CARE

FOLLOW-UP RECOMMENDATIONS

Close observation of visual acuity. The patient should report subjective improvement as the hypotony resolves.

Patient Monitoring

Every few days if the chamber is shallow or flat, or if there is a wound leak. When a bandage lens is in place, the treatment involves coverage with a topical fluoroquinolone q.i.d.

DIET

Patients at risk for hypotony should maintain good hydration.

PATIENT EDUCATION

• Educate patients about the cause and the implications of this condition. Better understanding may help the patient to be more compliant with treatment and follow-up care.

• Patients should also be warned that improvement in visual acuity often lags behind the resolution of hypotony.

PROGNOSIS

Prognosis varies with the cause and the extent of hypotony.

COMPLICATIONS

• Corneal decompensation, synechiae, cataract formation, and chronic retinal edema or folds may occur.

• If suprachoroidal hemorrhage develops, the results may be catastrophic for the eye; however close observation and drainage after 10 days when the blood is liquefied will often yield an excellent result.

• Prolonged hypotony may lead to pre-phthisis or phthisis bulbi.

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