What Is Corneal Dystrophy?
Corneal dystrophy is a group of inherited eye conditions that affect the cornea—the clear, dome-shaped window at the front of your eye. These genetic disorders cause a gradual buildup of abnormal material in one or more of the cornea's layers, making it cloudy or opaque over time.
Key characteristics define these conditions: they are genetic, progress slowly over years or decades, and typically affect both eyes, though not always symmetrically. Importantly, they are not caused by infection or inflammation, meaning the problem is intrinsic to the cornea's cellular health. This clouding is what leads to vision loss and other disturbances, especially in low-light conditions.
Why Corneal Dystrophy Worsens Vision at Night
To understand how corneal dystrophy affects vision, think of a healthy cornea as a clear window that focuses light precisely onto the retina. The deposits from dystrophy turn this window into something more like frosted glass, scattering light in multiple directions instead of focusing it cleanly. This light scatter is the root cause of most vision problems associated with the condition, particularly at night.
The Role of Pupil Dilation
In low light, the pupil naturally widens, or dilates, to let more light into the eye. This process exposes a larger surface area of the cornea. If abnormal deposits are present, this dilation forces light to pass through more of the cloudy, irregular tissue. This dramatically increases the amount of light that gets scattered, which intensifies visual distortions and makes night vision significantly worse than daytime vision.
Common Night Vision Symptoms
The increased light scatter from a dilated pupil leads to several distinct and challenging symptoms.
Debilitating Glare
Scattered light is perceived by the brain as overwhelming, uncomfortable brightness. This can create a "white-out" effect when facing oncoming headlights, momentarily blinding a driver to the road ahead. This makes night driving not just difficult, but hazardous.
Halos and Starbursts
Light sources like streetlights or traffic signals appear to have glowing rings (halos) or radiating streaks of light (starbursts) around them. These optical effects can make it hard to distinguish the shape or color of a light, turning a nighttime cityscape into a confusing and disorienting environment.
Reduced Contrast Sensitivity
The cloudiness from corneal dystrophy can "wash out" the visual world, reducing the sharp definition between different shades. This makes it difficult to see the edges of objects in dim lighting, such as curbs or stairs, which increases the risk of missteps and falls.
How Different Dystrophy Types Impact Vision
While most dystrophies cause glare and halos, the specific type—defined by which corneal layer is affected—determines how and when symptoms manifest. The location of the cloudiness directly influences the visual experience.
Fuchs' Dystrophy
This condition affects the innermost cell layer, the endothelium, which is responsible for pumping fluid out of the cornea. As these cells fail, the cornea swells with fluid, a condition called edema. This causes significant morning fog that may improve during the day and leads to severe glare as the excess fluid scatters light.
Lattice Dystrophy
Involving the cornea's thick middle layer, the stroma, this type features a web-like pattern of abnormal protein deposits. This lattice structure is very effective at scattering light, causing prominent starbursts and halos. This condition can also cause painful, recurring breaks on the corneal surface known as erosions.
Granular Dystrophy
Also a stromal dystrophy, this condition is characterized by distinct, crumb-like deposits. In the early stages, vision between the deposits can remain clear. However, as they grow and merge, they create a general haze that degrades contrast sensitivity and sharpness, making it harder to see in dim light.
Meesmann Dystrophy
Affecting the very front surface of the cornea, the epithelium, this condition leads to the formation of tiny cysts. Because the disruption is on the surface where light first enters the eye, it can create a constant sense of looking through a smudged window, causing glare and irritation.
Diagnosis and Management of Vision Symptoms
If symptoms like glare and halos begin to interfere with daily life, a comprehensive eye exam with an ophthalmologist is necessary. Using a slit lamp, the doctor can inspect the corneal layers to diagnose the specific type of dystrophy and create a tailored management plan.
Specialized Eyewear and Lens Coatings
One of the most immediate ways to manage glare is with glasses. Lenses with an anti-reflective (AR) coating reduce distracting reflections, while polarized sunglasses cut down on intense daytime glare. Some people find that yellow or amber-tinted lenses for night driving can enhance contrast and reduce the intensity of halos.
Medicated Eye Drops
For dystrophies that cause corneal swelling, such as Fuchs', hypertonic saline eye drops can provide temporary relief. These high-salt-concentration drops help draw excess fluid out of the cornea, which can reduce light scatter and improve clarity, especially for the morning fogging many experience.
Advanced Surgical Procedures
When conservative measures are no longer effective, surgery to replace the diseased corneal tissue with clear donor tissue is the primary option. Depending on which layers are affected, a surgeon may perform a partial-thickness transplant, like DMEK for Fuchs' dystrophy, or a full-thickness transplant (Penetrating Keratoplasty). These procedures are highly effective at restoring corneal clarity and resolving issues with glare and halos.
