The cornea is the clear “window” in the front of the eye that allows light rays to enter.
The cornea has three layers – the outer epithelium (or skin), a middle area called stroma and a delicate, single celled inner lining called the endothelium. The endothelium acts as a barrier to prevent water inside the eyeball from moving into and swelling the other layers of the cornea. The cells of the endothelium actively pump water from the cornea back into the eye.
If the endothelium does not function normally, then water moves into the cornea causing swelling. Swelling causes clouding of the cornea and blurred vision. The more corneal swelling or “edema,” the more severely the vision is blurred. Eventually, the outer corneal layer (epithelium) also takes on water, resulting in pain and more severe vision impairment. Epithelial swelling reduces vision by changing the normal curvature of the cornea. It causes a sight-limiting haze to develop. Epithelial swelling may also form small “blisters” on the corneal surface. When these “blisters” burst, extreme pain can occur.
Endothelial cells can be counted with special photographic methods. Most people are born with approximately 4,000 cells per square millimeter of the endothelial surface. These cells do not divide and cannot reproduce or replace themselves. As we age, we gradually lose endothelial cells.
Once lost, endothelial cells do not grow back. The remaining cells spread out to cover the empty spaces, trying to pump water from a larger area. The pump system becomes less efficient, causing corneal clouding, swelling and eventually, reduced vision. Fortunately, most people have enough endothelial cells throughout life to prevent corneal swelling or edema. If the cells are healthy and functioning properly, as few as 500 cells per square millimeter can maintain a clear cornea. If the cells are not healthy, fewer than 1000 cells per square millimeter may result in corneal swelling or edema.
Fuchs’ dystrophy (named after Dr. Fuchs) is an inherited condition that affects the delicate inner layer (endothelium) of the cornea. Patients with Fuchs’ dystrophy have endothelial cells that:
- Do not function as efficiently as normally
- Age and deteriorate more rapidly than normal cells
Fuchs’ dystrophy affects both eyes and is slightly more common in women then men. On average, half of the family members of an affected person may carry or suffer from the condition. The exact cause of Fuchs’ dystrophy is unknown. Hereditary, hormonal and inflammatory factors probably all play a role.
Signs and Symptoms:
In early stages, people with Fuchs’ dystrophy may wake up with blurred vision, which gradually clears over the day. That’s because during the day, water continuously evaporates from the surface of the eye and is replaced with water drawn from the inner compartments of the eye. Overnight, when we sleep with closed eyes, water cannot evaporate from the surface of the eye and accumulates in the cornea, causing slight swelling which blurs vision. Once eyes are opened throughout the day, evaporation reduces the water content and the thickness of the cornea, allowing for clearing of vision. In later stages, as the dystrophy worsens, evaporation is not enough to remove accumulated water in the cornea, and swelling and blurred vision last all day.
Typical complaints among people with Fuchs’ dystrophy include:
- Hazy vision that is often most pronounced in the morning
- Fluctuating vision
- Glare when looking at lights
- Light sensitivity
- Sandy, gritty sensation
- Episodes of sharp, sometimes incapacitating pain
Detection and Diagnosis:
Although doctors can often see early signs of Fuchs’ dystrophy in people in their 30s and 40s, the dystrophy rarely affects vision until people reach their 50s and 60s. Fuchs’ dystrophy is detected by examining the cornea with a slit lamp microscope that magnifies the endothelial cells thousands of times. The health of the endothelium is evaluated and monitored with pachymetry (which measures the thickness of the cornea) and specular microscopy (which photographs the cells for counting). As the dystrophy becomes more advanced, corneal clouding may make counting the cells impossible.
Fuchs’ dystrophy cannot be cured. Doctors are unable to treat the endothelial cells to make them work better or to become more numerous. However, blurred vision resulting from the corneal swelling can be controlled with medication. Salt solutions containing sodium chloride (Muro 128 drops or ointment, 2% or 5%) are often prescribed to draw fluid from the cornea and reduce swelling. Steroid eye drops may be helpful in specific situations.
Another simple technique that reduces moisture in the cornea is to hold a hair dryer at arm’s length, blowing air towards the face with the eyes open. This warm air flow increases evaporation of water from the cornea, temporarily decreases swelling, and may improve vision. Often very helpful in early stages, this technique may not be effective when swelling is severe, as in advanced stages.
Corneal transplantation is considered when vision deteriorates to the point that it interferes with daily activities and impairs a person’s ability to function normally. This surgery replaces the full thickness of the cornea, including the endothelium, with healthy layers. The cloudy cornea is replaced with clear corneal tissue.
Fuchs’ Dystrophy in Patients with Cataracts:
As people age, the lens within the eye often becomes cloudy, developing into a cataract. Cataract surgery is very common and has a very high success rate. Any eye surgery causes some damage to the delicate endothelial cell layer of the cornea, causing a reduction in the number of cells remaining to pump water from the cornea. If the number of endothelial cells is insufficient following cataract surgery, corneal swelling will develop, reducing vision. Corneal transplantation may be necessary to recover vision. When patients with Fuchs’ dystrophy develop cataract, it is important to carefully evaluate the status of the endothelium to decide whether the cornea is likely to continue to function well following cataract surgery. A recommendation may be made to combine cataract surgery with corneal transplantation. One combined surgery can achieve what would otherwise require two separate surgeries with a longer post-operative recovery.