History

The following should be assessed in patients with ocular hypotony:

Recent trauma or surgery, as follows:
- Glaucoma surgery with antimetabolites, a loosely sutured scleral flap, or a large track created to introduce a drainage device
- Any unsutured incision may be prone to leak, especially sutureless transconjunctival vitrectomy incisions; the incidence of hypotony is less using air-gas endotamponade than in fluid-filled eyes.^[4]
- Surgery requiring partial thickness scleral sutures, particularly in patients with myopia or abnormally thin tissue
- Blunt trauma can cause a transient lowering of intraocular pressure (IOP)
- Patients with a remote history of trauma can develop hypotony many years after the initial injury
- Unexpected hypotony with bleb tissue thinning after tube shunt has been reported in patients with a history of many previous anti-vascular endothelial growth factor injections.^[5]
History of iridocyclitis or systemic illnesses predisposing to uveitis
Blurred vision
Eye pain (usually a deep ache), especially with choroidal detachment (Hemorrhagic choroidal detachment can cause extreme pain.)
Signs and symptoms associated with retinal detachment
Use of IOP-lowering medications, including recent exposure to anesthesia
Severe dehydration, systemic hypertonicity, or acidosis
Pregnancy can contribute to IOP lowering.^[6]

Physical

See the list below:

Low intraocular pressure (≤5 mm Hg) after adjusting for extremely thin or thick corneal pachymetry: Individuals with very thin corneas (< 500 microns) may register low uncorrected tonometer readings without any clinical signs or symptoms of hypotony. Conversely, those with thick corneas (>600 microns) may exhibit symptomatic hypotony above an intraocular pressure of 6 mm Hg.
Shallowing of the anterior chamber
- Corneal edema and decompensation, especially in areas of corneal-iris touch (as is shown in the image below )
  
  Flat anterior chamber with iris-corneal touch following a phacotrabeculectomy.
  View Media Gallery
- Synechiae formation
- Corneal astigmatism
Seidel-positive wound leak (as is shown in the image below )

Seidel-positive wound leak around a conjunctival suture.
View Media Gallery
Large bleb following trabeculectomy or tube shunt (An eroded tube shunt is shown in the image below. )

Eroded tube shunt in a patient with rheumatoid arthritis.
View Media Gallery
Unplanned postoperative filtering bleb
Hyperopic shift/reduced axial length
Suspected traumatic globe rupture, especially if the following are present:
- 360° of subconjunctival hemorrhagic chemosis
- Peaked pupil
- Hyphema
- Intraocular foreign body
- Preexisting weakness in the globe integrity, such as staphyloma, coloboma, or an old incision
Inflammatory cells and flare in the anterior chamber
Serous, hemorrhagic, or tractional ciliochoroidal detachment
Accelerated cataract formation
Hypotony maculopathy
- Macular thickening and folds seen on examination or optical coherence tomography (OCT) of the retina
- Vascular engorgement and tortuosity
- Optic disc swelling
Cyclodialysis cleft seen on gonioscopy (viscoelastic in the anterior chamber can enhance visualization)
Retinal detachment
- The anterior chamber is often deeper than usual when a retinal detachment is present.
- Vitreous hemorrhage, evidence of penetrating injury, traction, or retinal hole is visible on funduscopic examination.
Neovascularization of the iris in the setting of possible ocular ischemia

Causes

Unilateral hypotony may be caused by the following:

Wound leak
Overfiltering or inadvertent bleb
Ciliary body detachment – Serous, hemorrhagic, or tractional
Cyclodialysis cleft
Inflammation - Iridocyclitis or blunt trauma
Retinal detachment or retinotomy
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
External pressure on the eye, often inadvertently during sleep, especially with use of a CPAP mask

Bilateral hypotony may be caused by the following:

Systemic hypertonicity or acidosis - Dehydration, uremia, uncontrolled diabetes, or use of hyperosmotic agents
Myotonic dystrophy^[7]
Pregnancy in predisposed women

Complications

Transient or permanent visual impairment may result from corneal changes, accelerated cataract formation, choroidal fluid, choroidal folds, maculopathy with disturbance of the retinal pigment epithelium (RPE), cystoid macular edema, optic disc edema, or progressive neuropathy. Hypotony increases the risk of suprachoroidal hemorrhage, which can result in severe vision loss.

Hypotony in the setting of an incompetent corneal or limbal wound can predispose the patient to epithelial ingrowth.

Severe chronic hypotony can ultimately lead to phthisis.

Differential Diagnoses

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