Ocular hypotony, or ocular hypotension, or shortly hypotony, is the medical condition in which intraocular pressure (IOP) of the eye is very low.
Normal IOP ranges between 10–20 mm Hg.[1] The eye is considered hypotonous if the IOP is ≤5 mm Hg (some sources say IOP less than 6.5 mmHg).[2][3]
Ocular hypotony is divided into statistical and clinical types. If intraocular pressure is low (less than 6.5 mm Hg) it is called statistical hypotony, and if the reduced IOP causes a decrease in vision, it is called clinical.[4]
Hypotony may occur either due to decreased production of aqueous humor or due to increased outflow. Hypotony has many causes including post-surgical wound leak from the eye, chronic inflammation within the eye including iridocyclitis, hypoperfusion, tractional ciliary body detachment or retinal detachment.[5] Eye inflammation, medications including anti glaucoma drugs, or proliferative vitreoretinopathy causes decreased production.[6] Increased outflow or aqueous loss may occur following a glaucoma surgery, trauma, cyclodialysis cleft or retinal detachment.[6]
Decreased IOP may lead to phthisis bulbi.[3] Hypotony maculopathy is another complication caused by very low IOP.[7]
Treatment of hypotony is depending on the cause of the condition.[6] Chronic ocular hypotony may be treated with intraocular injection of sodium hyaluronate.[8] If the cause of hypotony is an over filtering bleb, cycloplegia using atropine may be used.[2]
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