Definition

Decreased visual function and other ocular symptoms related to low IOP.

Mild-to-severe pain, reduced vision, or may be asymptomatic. Patient with recent glaucoma filtering surgery may complain of “excessive tearing.”

Critical

Low IOP, usually ≤5 mm Hg, but may occur with an IOP as high as 10 mm Hg. Nonetheless, some patients may tolerate lower  IOP and may not develop sequelae of hypotony despite IOP ≤5 mm Hg.

Other

Corneal edema and folds, corneal decompensation, aqueous cell and flare, shallow or flat anterior chamber, retinal edema, hypotony maculopathy, chorioretinal folds, serous choroidal detachment, suprachoroidal hemorrhage, optic disc swelling, and retinal vascular tortuosity.

• Postsurgical: Wound or bleb leak, overfiltering bleb or glaucoma drainage device (more common with use of antimetabolites during surgery), cyclodialysis cleft (disinsertion of the ciliary body from the sclera at the scleral spur), scleral perforation (e.g., from a superior rectus bridle suture or retrobulbar injection), iridocyclitis, retinal, or choroidal detachment, etc.

• Posttraumatic: Same causes as postsurgical.

• Rhegmatogenous retinal detachment.

• Pharmacologic: Usually from an oral carbonic anhydrase inhibitor in combination with a topical β-blocker. Also associated with cidofovir.

• Systemic (bilateral hypotony): Conditions that cause blood hypertonicity (e.g., dehydration, uremia, hyperglycemia), myotonic dystrophy, pregnancy, etc. Rare.

• Vascular occlusive disease (e.g., ocular ischemic syndrome, giant cell arteritis, central retinal vein or artery occlusion): Usually mild hypotony due to decreased aqueous humor production from ciliary body hypoperfusion. Rare.

• Uveitis: Secondary to ciliary body shutdown.

1. History: Recent ocular surgery or trauma? Systemic symptoms (nausea, vomiting, drowsiness, polyuria)? History of renal disease, diabetes, or myotonic dystrophy? Medications?

2. Complete ocular examination, including slit-lamp evaluation of surgical or traumatic ocular wounds, IOP check, grading of anterior chamber depth, gonioscopy to rule out a cyclodialysis cleft, evaluation of the macula for folds, and indirect ophthalmoscopy to rule out retinal or choroidal detachment.

3. Seidel test (with or without gentle pressure) to rule out a wound leak. See Appendix 5, Seidel Test to Detect a Wound Leak.

4. OCT of the macula to evaluate for macular folds (evidenced by rippled appearance of the retinal pigment epithelium [RPE]).

   NOTE A wound leak may drain under the conjunctiva, producing an inadvertent filtering bleb. May be seen in old extracapsular cataract extraction wounds, which are large and may not completely close. Seidel test will then be negative.

5. B-scan US when the fundus cannot be seen clinically. Consider UBM or anterior segment OCT to aid in anterior chamber assessment, especially evaluation for cyclodialysis cleft. Macular OCT may be used for diagnosis confirmation and therapeutic monitoring.

6. Systemic workup in bilateral cases, including basic metabolic panel.

Repair of the underlying disorder may be needed if symptoms are significant or progressive. Low IOP, even as low as 2 mm Hg, may not cause problems or symptoms and may be observed.

Wound Leak

1. Large wound leaks: Suture the wound closed.

2. Small wound leaks: Can be sutured closed or patched with an antibiotic ointment (e.g., erythromycin) and a pressure dressing or bandage soft contact lens for one night to allow the wound to close spontaneously. Rarely, cyanoacrylate glue is applied to small wound leaks and covered with a bandage contact lens. Aqueous suppressants are often given concurrently to reduce aqueous flow through the wound.

3. Wound leaks under a conjunctival flap: Repair required only if vision affected or for secondary ocular complication such as a flat anterior chamber or infection.

Shallow Anterior Chamber

If the anterior chamber is very shallow or flat, start a topical cycloplegic (e.g., cyclopentolate 1% t.i.d. or atropine 1% daily) and topical steroid (e.g., prednisolone acetate 1% or difluprednate 0.05% q2h), as long as no infectious process is suspected. This should rotate the iris-lens complex posteriorly and can deepen the chamber to prevent corneal endothelial damage. 

Overfiltering Bleb

Compression with a large bandage soft contact lens can at times reduce bleb exuberance. Surgical repair in the operating room may be required with compression sutures (transconjunctivally or directly over the scleral flap), placement of a corneal or scleral patch graft over a shrunken scleral flap, or removal of the aqueous shunt device from the anterior chamber.

Cyclodialysis Cleft

Reattach the ciliary body to the sclera by chronic atropine therapy, diathermy, suturing, cryotherapy, laser photocoagulation, or external plombage. See 3.8, Iridodialysis/Cyclodialysis.

Scleral Perforation

The site may be closed by suturing or cryotherapy.

Iridocyclitis

Topical steroid (e.g., prednisolone acetate 1% or difluprednate 0.05% q1–6h) and a topical cycloplegic (e.g., cyclopentolate 1% t.i.d.). See 12.1, Anterior Uveitis (Iritis/Iridocyclitis).

Retinal Detachment

Surgical repair. See 11.3, Retinal Detachment.

Choroidal Detachment

See 11.27, Choroidal Effusion/Detachment. Surgical drainage of the choroidal effusion along with reformation of the eye and anterior chamber is indicated for any of the following:

1. Retinal apposition (“kissing” choroidal detachments).

2. Lens–corneal touch (needs emergent attention).

3. A flat or persistently shallow anterior chamber accompanied by a failing filtering bleb or an inflamed eye.

4. Corneal decompensation.

If these findings are not present, choroidal effusion can be managed conservatively and observed closely with a topical cycloplegic and topical steroids for a period of time.

Pharmacologic

Reduce or discontinue the IOP-reducing medications.

Systemic Disorder

Refer to an internist.

NOTE In myotonic dystrophy, the hypotony is rarely severe enough to produce deleterious effects, and treatment of hypotony, from an ocular standpoint, is unnecessary.

If the vision is good, the anterior chamber is well formed, and there is no wound leak, retinal detachment, or kissing choroidal detachments, then the low IOP poses no immediate problem. Treatment and follow-up are not urgent. Fixed retinal folds in the macula may develop from long-standing hypotony.