Hypotony of the eye refers to abnormally low intraocular pressure (IOP). The pressure inside the eye is maintained by a fluid called aqueous humor, and normal IOP falls within the range of 10 to 21 millimeters of mercury (mm Hg). Hypotony is defined as an IOP of 5 mm Hg or less, especially when associated with a decline in vision. Unlike glaucoma, which involves high eye pressure, excessively low pressure can also compromise the eye’s structure and function. The effects of low IOP can differ among individuals, with some experiencing no issues while others suffer from vision loss.
Causes of Low Eye Pressure
A primary cause of hypotony is complications following eye surgery. Procedures designed to treat glaucoma, such as a trabeculectomy, create a new drainage channel for aqueous humor. If this channel allows too much fluid to exit, the internal pressure can drop excessively. Other intraocular surgeries can also lead to fluid leaks and low pressure.
Eye trauma is another factor. A penetrating injury can cause a direct leak of aqueous humor, while blunt force trauma can damage internal structures that produce or regulate fluid. This disrupts the balance needed to maintain normal IOP.
Ocular inflammation, particularly uveitis, can also be a source of low eye pressure. Uveitis involves inflammation of the ciliary body, which is responsible for producing aqueous humor. When inflamed, its ability to produce this fluid can be reduced, leading to a decrease in IOP.
A long-standing retinal detachment can result in hypotony. If the retina detaches from its normal position, it can affect the function of the eye’s internal systems. This disruption can interfere with the production and flow of aqueous humor, causing a gradual decline in eye pressure. Lastly, certain medications can cause an excessive drop in eye pressure as a side effect.
Associated Symptoms and Complications
When symptoms occur, they often include a significant blurring or distortion of vision. Patients might also experience a dull ache or pain in the eye, and in some instances, the eyeball may feel physically softer to the touch. These symptoms arise because the low pressure compromises the structural integrity of the globe.
A complication is hypotony maculopathy, where low pressure causes the scleral wall to collapse inward, leading to the formation of wrinkles or folds in the retina and the underlying choroid. Since the macula is responsible for sharp, central vision, these folds can severely distort what a person sees, making detailed tasks like reading difficult.
Another issue is choroidal effusion, an accumulation of fluid in the space between the sclera and the choroid. This fluid buildup can further reduce the production of aqueous humor, worsening the hypotony. Chronically low eye pressure is also associated with the accelerated formation of cataracts, which is a clouding of the eye’s lens.
The end-stage outcome of untreated hypotony is phthisis bulbi. In this condition, the eye shrinks, becomes disorganized, and permanently loses all function. The eye essentially becomes a non-viable, scarred organ, representing a complete structural and functional collapse.
Diagnostic Process
The diagnostic process begins with tonometry, the standard method for measuring intraocular pressure (IOP). An ophthalmologist will use a device, often a Goldmann applanation tonometer, to get an accurate reading of the pressure inside the eye.
A slit-lamp examination is also performed, allowing the doctor to inspect the eye’s structures under high magnification. During this exam, the physician looks for signs such as a leak from a previous surgical site, which can be identified using a Seidel dye test. The exam also helps identify inflammation or other abnormalities causing the low pressure.
To assess for complications, a fundus examination is conducted to view the structures at the back of the eye, like the retina and optic nerve. This allows the doctor to check for the retinal folds of hypotony maculopathy or signs of choroidal detachment.
In complex cases, specialized imaging tests may be required. An ultrasound biomicroscopy (UBM) or optical coherence tomography (OCT) can provide detailed, cross-sectional images of the eye’s internal structures. These techniques help pinpoint a fluid leak or identify subtle problems like a detached ciliary body, which may not be visible during a standard examination.
Treatment Approaches
Treatment for hypotony focuses on the underlying cause. If a leak from a previous surgery or a traumatic wound is the cause, surgical intervention may be necessary to repair the opening. A surgeon might revise a glaucoma filter that is draining too much fluid or suture a wound that has not healed properly.
When ocular inflammation like uveitis is the culprit, treatment involves controlling the inflammation with medication. Anti-inflammatory drugs, such as topical corticosteroids, can reduce inflammation in the ciliary body. This helps restore its ability to produce aqueous humor and can also directly contribute to an increase in IOP.
Medical management may also involve specific eye drops like atropine. This cycloplegic medication can help deepen the eye’s anterior chamber and stabilize its internal structures. This can raise the pressure and alleviate symptoms while the root cause is being addressed.
In mild cases with no vision problems or structural complications, a doctor might recommend careful observation. This approach involves regular monitoring of eye pressure and vision. This is reserved for cases where the potential risks of intervention outweigh the benefits.