Hypotony may be defined as an intraocular pressure (IOP) of 5 mm Hg or less, and if chronic, this condition can lead to secondary retinal changes. 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:
(a) Excessive aqueous outflow. Hypotony is a potential complication following glaucoma surgery. e.g. 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 e.g. wound leak.
(b) Inadequate aqueous humor 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.
Mild to moderate blurring of vision or metamorphopsia may be reported. May have mild to severe pain, depending upon the etiology.
(a) Hypotony: By definition, the intraocular pressure is reduced in hypotony, usually less than 5mmHg. 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 humor passing out through the wound). Gonioscopy may show cyclodialysis, a disinsertion of the ciliary body from the scleral spur.
(b) 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.
(c) Signs associated with the underlying etiology may be present, in relation to surgery, trauma, retinal detachment, phthisis or inflammation.
Rare complication after trauma or ocular surgery, particularly after use of anti-metabolites
Temporary or permanent effect on vision can result from hypotony. Severe and persistant hypotony can lead to phthisis.
Vitreo-macular traction syndrome, macular hole, macular edema. There is a range of other possible causes of choroidal folds (See Table, Choroidal folds).
Choroidal detachment, Angle recession and glaucoma
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. Hyperfluoresence may also be present at the optic disc, with leakage at the macular. Blood tests may be indicated if the hypotony is bilateral.
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.
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 is non-urgent if vision is good, any hypotonic signs have been remedied and the underlying etiology has been addressed. However, if risk factors remain, then ongoing review of the intraocular pressure and retinal signs may be beneficial.
Swelling of the optic nerve head and surrounding tissue associated with hypotony