Glaucoma is characterized by progressive damage to the optic nerve, which transmits visual information from the eye to the brain. This damage is frequently associated with elevated intraocular pressure (IOP), caused by a malfunction in the eye’s natural fluid drainage system. While many people assume glaucoma affects both eyes equally, this is often not the case. It is possible to have glaucoma in only one eye, known as unilateral glaucoma. Even when both eyes are affected, the disease is frequently asymmetrical, meaning one eye can be significantly more advanced or progress faster than the other.
Understanding Why Glaucoma Can Be Asymmetrical
The distinction between different types of glaucoma helps explain why the condition might affect only one eye. Glaucomas are generally classified into two categories: primary and secondary. Primary glaucomas, such as Primary Open-Angle Glaucoma (POAG), are typically systemic conditions with no identifiable underlying cause. These types usually affect both eyes, though one eye may show damage sooner due to anatomical or biological differences.
In contrast, secondary glaucomas arise as a complication of another specific, localized condition or event. Since the underlying cause is often confined to one eye, these secondary forms are the most common reason for a unilateral diagnosis. This localized trigger creates a physical or biological impediment to fluid outflow in only the affected eye, causing pressure to build up.
Key Causes of Glaucoma Affecting Only One Eye
Traumatic Glaucoma
A specific physical injury to the eye is one of the most common causes of unilateral glaucoma, resulting in traumatic glaucoma. Blunt force trauma can damage the trabecular meshwork, the spongy tissue responsible for draining fluid from the eye. This injury can tear or scar the drainage angle, leading to poor fluid regulation and a subsequent increase in intraocular pressure, sometimes years after the initial event.
Inflammatory Glaucoma (Uveitis)
Inflammatory conditions localized to one eye, such as uveitis, can also trigger a secondary glaucoma. Uveitis involves inflammation of the middle layer of the eye, which causes inflammatory cells and debris to clog the trabecular meshwork. This blockage reduces the rate at which aqueous humor exits the eye, leading to a rise in pressure and optic nerve damage.
Steroid-Induced Glaucoma
Steroid-induced glaucoma occurs when a person is sensitive to corticosteroids. If steroid medications are administered topically, such as in the form of eye drops or injections, to treat a condition in only one eye, the resulting pressure elevation will often be restricted to that eye. The steroids interfere with the function of the trabecular meshwork, increasing resistance to fluid outflow and causing a pressure spike.
Pseudoexfoliation Syndrome
Certain anatomical or structural syndromes frequently present with significant asymmetry. Pseudoexfoliation syndrome involves the deposition of flaky, dandruff-like material onto various structures within the eye, including the drainage angle. If this material accumulates heavily in one eye, it can severely obstruct fluid outflow and cause glaucoma in that eye long before the other eye shows any signs of damage.
Monitoring and Protecting the Unaffected Eye
A diagnosis of unilateral glaucoma places the currently healthy eye in the status of a “glaucoma suspect.” Even with a clear secondary cause, there is a possibility that underlying anatomical features could affect the second eye over time. The management strategy for the unaffected eye focuses on rigorous monitoring to catch any signs of conversion to glaucoma as early as possible.
Regular, consistent monitoring is essential and involves a suite of diagnostic tests performed frequently, often every three to six months. These appointments include:
- Checks of intraocular pressure (IOP), which can fluctuate throughout the day.
- Visual field tests to look for subtle losses in peripheral vision, which is typically affected first.
- Structural imaging using Optical Coherence Tomography (OCT) scans.
- Detailed examination of the optic nerve and retinal nerve fiber layer.
The OCT provides a detailed view of the nerve tissue, allowing clinicians to detect minute thinning that may precede measurable vision loss. Identifying structural changes early allows for immediate treatment to prevent the onset of functional damage. If the cause was steroid use, similar medications must be carefully avoided or closely monitored. The overall goal is to maintain the integrity of the unaffected eye indefinitely by establishing a safe target IOP and adjusting treatment if any change appears.