History
The following should be assessed in patients with ocular hypotony:
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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]
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History of iridocyclitis or systemic illnesses predisposing to uveitis
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Blurred vision
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Eye pain (usually a deep ache), especially with choroidal detachment (Hemorrhagic choroidal detachment can cause extreme pain.)
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Signs and symptoms associated with retinal detachment
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Use of IOP-lowering medications, including recent exposure to anesthesia
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Severe dehydration, systemic hypertonicity, or acidosis
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Pregnancy can contribute to IOP lowering. [6]
Physical
See the list below:
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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.
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Shallowing of the anterior chamber
Corneal edema and decompensation, especially in areas of corneal-iris touch (as is shown in the image below )
Synechiae formation
Corneal astigmatism
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Seidel-positive wound leak (as is shown in the image below )
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Large bleb following trabeculectomy or tube shunt (An eroded tube shunt is shown in the image below. )
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Unplanned postoperative filtering bleb
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Hyperopic shift/reduced axial length
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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
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Inflammatory cells and flare in the anterior chamber
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Serous, hemorrhagic, or tractional ciliochoroidal detachment
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Accelerated cataract formation
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Hypotony maculopathy
Macular thickening and folds seen on examination or optical coherence tomography (OCT) of the retina
Vascular engorgement and tortuosity
Optic disc swelling
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Cyclodialysis cleft seen on gonioscopy (viscoelastic in the anterior chamber can enhance visualization)
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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.
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Neovascularization of the iris in the setting of possible ocular ischemia
Causes
Unilateral hypotony may be caused by the following:
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Wound leak
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Overfiltering or inadvertent bleb
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Ciliary body detachment – Serous, hemorrhagic, or tractional
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Cyclodialysis cleft
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Inflammation - Iridocyclitis or blunt trauma
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Retinal detachment or retinotomy
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Ocular ischemia
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Scleral perforation with needle or suture, or scleral rupture following trauma
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Chemical cyclodestruction from antimetabolites
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Photocoagulation or cryoablation of the ciliary body
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Pharmacologic aqueous humor suppression
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External pressure on the eye, often inadvertently during sleep, especially with use of a CPAP mask
Bilateral hypotony may be caused by the following:
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Systemic hypertonicity or acidosis - Dehydration, uremia, uncontrolled diabetes, or use of hyperosmotic agents
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Myotonic dystrophy [7]
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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.
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Seidel-positive wound leak around a conjunctival suture.
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Conjunctival advancement flap sewn over a diffusely incompetent bleb.
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Eroded tube shunt in a patient with rheumatoid arthritis.
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Flat anterior chamber with iris-corneal touch following a phacotrabeculectomy.
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Autologous blood injected into an overfiltering bleb to create a blood patch.
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B-scan ultrasound of choroidal effusions before and after surgical drainage.
