Hypotony is low intraocular pressure (IOP). Normal IOP is usually between 12 and 22 mm Hg. When the pressure drops to 5 mm Hg or less, the individual is said to be having hypotony.
In ocular hypotony, the low pressure makes the eye to turn soft. At this point, blinking can distort the shape of the eye and vision. The other problem is the collection of fluid behind the retina hence interfering with vision. Loss of acuity in the centre of an individual’s vision field is indicative of IOP. Pressure should neither be too high nor too low. High pressure results in conditions like glaucoma while low pressure causes hypotony. Hypotony can occur in one or both eyes within two weeks of surgery.
Also Known As
Causes and Risk Factors
The most common cause of hypotony is surgery such as primary glaucoma filtration. The incisions made on the eye may cause leakage resulting in low pressure. Hypotony can occur with increased outflow of aqueous humor (clear liquid in the front part of the eye). A surgical wound leak, cyclodialysis cleft (when the ciliary body is separated from the scleral spur), overfiltering bleb (area from surgery where the fluid filters), scleral rupture and so on are due to increased aqueous humor outflow.
Other causes of hypotony include trauma and inflammation. The production of aqueous in the ciliary body is lessened by inflammation while increasing the outflow. Another common cause is retinal detachment.
Glaucoma patients are at risk of developing maculopathy hypotony through the use of antifibrotic agents during glaucoma surgery. Further, young males are also more likely to develop hypotony. People with myopia and systemic illnesses can also develop hypotony.
Signs & Symptoms
Signs that hypotony has occurred may include:
A cornea that develops Descemet folds, astigmatism and edema
- Cataract formation
- Choroidal detachments
- Shallow, flat, anterior chamber
Oftentimes hypotony may present no symptoms. Each eye is unique and may respond to low pressure differently. When symptoms develop, they may include the following:
- Blurred or loss of vision
- Sudden bleeding below the retina
- Severe throbbing pain
The eye professional checks for IOP using tonometry. Goldmann applanation tonometry is the most reliable and accurate method. It is possible to obtain false results when the lens meets with the cornea during applanation. More checks include a slit lamp examination, seidel testing (to reveal ocular leaks), and gonioscopy (to look for cyclodialysis clefts). If gonioscopy is unsuccessful, then an ultrasound should be done. To check the retinal and choroidal changes, an anterior segment optical coherence tomography (OCT) may be performed.
Treatment of ocular pressure is directed toward normalizing the pressure in the eye.
Treatment depends on the cause. A wound or a bleb leak is treated using aqueous suppressants, oversized contact lenses and surgery.
Hypotony caused by inflammation can be treated by topical corticosteroids. These drugs increase the production of aqueous humor and IOP. To intensify the anterior chamber and lessen contact between the cornea and iris, atropine can be used.
Post-surgical leaks may be treated in a number of ways. Low pressure in the early post-operative stage will often go away on its own. However, low pressure can cause loss of fluid in the shallow anterior chamber which should be treated immediately. The shallow chamber is injected with thick fluid by use of a tiny needle to help re-inflate it.
Patching and wound revision can help to treat overfiltering blebs. Blood drawn from the arm may be injected into the bleb. The injection helps to block the drainage channel resulting in increased pressure. Also, using viscoelastics (a special kind of substance) can help reshape the anterior chamber if it’s shallow.
Surgery is needed for lasting hypotony to reduce the amount of fluid draining from the eye. Sutures are used to tighten the flap controlling the fluid’s flow using fibrin glue. This procedure can be an outpatient operation.
Retinal detachments can be repaired surgically. Also, vitrectomy can be done for persistent chorioretinal folds.
Laser can be applied to the base of the bleb. In addition, a cyclodialysis cleft can be treated with laser or surgical suture.
Hypotony causes several secondary structure-related complications. The complications include hypotony maculopathy, phthisis bulbi, papilledema and ciliochoroidal detachment. These conditions can lead to decreased vision. Hypotony can also lead to swollen optic disks, swollen retinal vessels and folds in the choroid and retina.
For vision to be recovered, early detection and correction is necessary. A delay may lead to loss of vision.
Surgical-related causes of hypotony may be preventable. Surgeons can take measures to decrease the risk of complications following glaucoma filtration surgery. Antimetabolites should be used carefully.