Low eye pressure occurs when there is less fluid between the lens and the cornea of the eye than normal. The fluid, called aqueous humor, is usually produced and drained at a steady rate to maintain pressure levels in the eye and help the organ maintain its normal shape. If there is not enough fluid, a person can experience pain and changes in vision. Most cases of low eye pressure are acute and related to injuries or medication use, but some people suffer chronic problems in one or both eyes. Treatment depends on the underlying cause and may include taking medications, undergoing surgery, or a combination of the two.

Also called ocular hypotony, low eye pressure can be the result of too much drainage or insufficient production of aqueous humor. A person may develop the condition after a traumatic eye injury as fluid leaks out of lacerations on the cornea. A detached retina can also create a pathway for fluid to escape and lower pressure. Severe eye infections, conditions that disrupt blood flow, and dehydration may be responsible for symptoms when there is no history of eye trauma. In addition, it is common to experience a mild, temporary drop in eye pressure following glaucoma surgery.

The symptoms of low eye pressure can vary, and many people with mild conditions do not experience problems at all. A person may have occasional or chronic eye pain, blurred vision, and swelling in and around the eyeball. Occasionally, inflammation causes redness and increased tearing as well. A cloudy spot called a cataract can develop on the eye if low eye pressure is not diagnosed and treated appropriately.

Tonometry is a test that ophthalmologists use to measure aqueous humor concentrations in units called millimeters of mercury (mmHg). Normal tonometry readings fall between 10 and 21 mmHg. A person is typically diagnosed with low eye pressure if tonometry readings are at or below 5 mmHg and he or she has related symptoms. A doctor can also review family and medical history, results from blood tests, and current medication use to help identify the underlying cause of a patient's low eye pressure.

There are no medications available that are designed specifically to raise pressure levels in the eyes. Instead, doctors treat low eye pressure by treating the underlying problems. Patients who have eye injuries are often given anti-inflammatory topical ointments or eye drops. Oral or topical antibiotics may be prescribed if symptoms develop after glaucoma surgery or infection. If problems become chronic, surgery may be necessary to repair damaged tissue, reattach the retina, clear up a cataract, or partially block a drainage canal.