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Hypotony disrupts normal fluid flow patterns within the intraocular tissues and is liable to promote transudation of serum out of the choroidal vasculature, causing accumulation of serous fluid and lifting of the choroid.
Hypotony usually occurs as a complication of an underlying ocular disorder, often surgical or traumatic or secondary to inflammation:
? Excessive aqueous outflow. Hypotony is a potential complication following glaucoma surgery - eg wound leak or dysfunctional filtering bleb. Excess outflow can occur in trauma associated with cyclodialysis cleft. Hypotony is a very rare complication after cataract surgery, eg wound leak.
? Inadequate aqueous humour production in altered ciliary body function, such as iridocyclitis, tractional detachment, or hypoperfusion. Bilateral hypotony can result from systemic conditions that cause blood hypertonicity and other conditions.
Symptoms
Mild to moderate blurring of vision or metamorphopsia may be reported. There may be mild to severe pain, depending upon the etiology.
Signs
? Hypotony: By definition, the intraocular pressure is reduced in hypotony, usually less than 5mm Hg. The anterior chamber may be shallow or flat ( < 2mm central depth). If there is a corneal wound leak, a positive Seidel sign may be present (focal dilution of fluorescein in the tear film, due to aqueous humour passing out through the wound). Gonioscopy may show cyclodialysis, a disinsertion of the ciliary body from the scleral spur.
? Maculopathy and other retinal signs: Chorioretinal folds may radiate temporally from the optic disc. The retinal pigment epithelium (RPE) may be visibly thrown into folds. Around the fovea radiating folds may be evident. The optic disc and peripapillary chorio-retina may appear swollen.
? Signs associated with the underlying aetiology may be present, in relation to surgery, trauma, retinal detachment, phthisis or inflammation.
Prevalence
Rare complication after trauma or ocular surgery, particularly after use of anti-metabolites.
Significance
Temporary or permanent effect on vision can result from hypotony. Severe and persistant hypotony can lead to phthisis.
Differential Diagnosis
Vitreo-macular traction syndrome, macular hole, macular oedema. There is a range of other possible causes of choroidal folds.
See also
Choroidal detachment Angle recession and glaucoma.
Management
Additional investigations
Fluorescein angiography or ocular coherence tomography may be used to confirm the nature of the retinal and choroidal changes. Ocular coherence tomography may also be used to rule out vitreous tractional membranes. Fluorescein angiography will show alternating hyper- and hypo-fluorescent lines related to the folds. Hyperfluorescence may also be present at the optic disc, with leakage at the macula. Blood tests may be indicated if the hypotony is bilateral.
Incisional surgery
Surgical correction of the underlying cause of the hypotony is usually necessary. Management is primarily surgical in nature as there are no standard medications available with a primary action for raising IOP.
Topical medication
A topical cycloplegic, topical antibiotic for wound leak, topical steroids for uveitis.
Prognosis and Advice
Visual improvement and resolution of the choroidal folds will usually result from treatment of the hypotony maculopathy. There may be residual linear RPE alterations and pigment changes as a chronic effect of the folding.
Review
Review is non-urgent if vision is good, any hypotonic signs have been remedied and the underlying aetiology has been addressed. However, if risk factors remain, then ongoing review of the intraocular pressure and retinal signs may be beneficial.