What is Fuchs' Dystrophy?
Fuchs' dystrophy is an inherited disease of the cornea in which the innermost layer of the cornea, called the endothelium, becomes dysfunctional and may result in decreased vision. The front part of a normal eye is filled with fluid called the aqueous. However, the cornea, which separates the outside air from the aqueous fluid inside the eye, must maintain a proper balance of moisture in order to maintain its clarity. To accomplish this task, the inside of the cornea is lined with a specialized layer of cells called the endothelium. The endothelial cells function as one-way pumps, drawing fluid out of the cornea and pumping it back into the eye. By so doing, the cornea, despite being in direct contact with the aqueous eye fluid, doesn't become overly hydrated and maintains clarity.
In Fuchs' dystrophy, the endothelial cells are slowly replaced with small collagen bumps called guttata. Guttata may first appear in the cornea in the 20s and 30s, though rarely cause any symptoms until later in life. As a person ages, the guttata may slowly increase in number and size. In the process, the endothelial cells surrounding them may slowly die. When a critical number of endothelial cells are lost, usually by the age of 50 to 60 years, the pump function of the endothelium may be overwhelmed and the cornea starts to swell with eye fluid. As the swelling worsens, the vision may start to decrease. In cases where large amounts of guttata exist on the cornea, the vision may also become compromised even without corneal swelling from irregular scattering of light passing through the dense guttata layer.
Cause of Fuchs' Dystrophy
Fuchs' dystrophy is caused by an inherited malfunction in the way the inner lining cells of the cornea behave. The gene is transferred from parent to child in an autosomal dominant fashion, which means that each child of an affected parent has a 50% chance of developing the disease. Though many family members may have Fuchs' dystrophy, its effects may vary greatly from one family member to the next. As such, some individuals with Fuchs' dystrophy will have signs of the disease visible only to a doctor examining their corneas with a slit lamp, and will never suffer any visual loss from the disorder. Other individuals who have worse forms of the disease may suffer slowly progressive visual loss.
Symptoms of Fuchs' Dystrophy
Fuchs' dystrophy is usually asymptomatic until a person reaches 50 to 60 years of age. For individuals with worse forms of the disease, the endothelial cells of the cornea may become so compromised enough that the cornea begins to swell with eye fluid. This swelling is usually gradual over many weeks or months and may be so slow that it is not immediately noticeable. When the swelling becomes advanced enough, a person may notice that the vision seems not as sharp as it used to be. The vision may often be worse in the morning, due to swelling of the cornea overnight, and improve as the day goes on while the eyes are open and exposed to the drying effect of the air. Fuchs' dystrophy patients may also complain of more glare in sunlight conditions and more difficulty seeing in low light conditions. As the swelling becomes severe, the vision may decline greatly, causing true impairment of a person's daily living activities.