Fuchs' corneal dystrophy represents an inherited disease of the cornea. It affects both eyes and may progress to corneal swelling and loss of vision. (FIG. 1) When this occurs, corneal transplant surgery may be necessary. Fortunately, there is an excellent prognosis for maintaining good vision long term.

The cornea is the clear outer layer of the eye. It consists of 5 layers. (FIG. 2) The innermost layer is called the endothelium. There is a natural tendency for fluid within the eye to enter the cornea and cause it to swell. The endothelium is responsible for pumping out this fluid from the cornea and maintaining a relative state of dehydration. (FIG. 3a) It is in this state that the cornea is transparent and light may be transmitted and focused for clear vision. If the fluid cannot be pumped out, then the cornea swells and looses its transparency. (FIG. 3b) Light cannot be focused and vision is blurred.

The corneal endothelium is a one-cell layer on the innermost surface of the cornea. A given number or density of endothelial cells is present at birth, usually about 5,000 cells per square millimeter. There is a normal, progressive and slow loss of endothelial cells with aging. By the 40's, the cell count has dropped to about 3,000 cells/mm2. By the 70's or 80's this may be 2,000 cells/mm2. At this cell count there are still plenty of healthy cells to maintain corneal clarity. With Fuchs' corneal dystrophy, the rate of cell loss is accelerated. By the 5th or 6th decade of life, too many cells may have deteriorated and been lost, and the cell count may have dropped to less than 500 cells/mm2. (FIG. 4) Below 500 cells/mm2, the cornea begins to show swelling, and the vision becomes blurred. Special diagnostic equipment called a specular microscope and ultrasonic pachymeter are used to measure the corneal endothelium cell density and determine the presence of corneal swelling.

As the swelling develops, patients with Fuchs' dystrophy may ex-
perience a fluctuation of vision. They first describe cloudy vision early in the morning that seems to clear later in the day. As the swelling progresses, the vision remains cloudy longer during the day and eventually remains cloudy throughout the day. In the early stages of the swelling, medications may be helpful; however, the underlying problem of progressive endothelial cell loss cannot be halted.

Because this is an inherited condition, there is often a family history of Fuchs' dystrophy or corneal transplant surgery. The inheritance pattern is autosomal dominant, which means that 1/2 of the offspring of an affected individual (both male and female) will receive the gene for Fuchs' dystrophy and are at risk for developing this corneal deterioration. Specular microscopy can be performed to detect the early stages of this condition and may be useful to screen the offspring of an affected person.

Once the vision is cloudy, corneal transplant surgery is recommended. The new donor cornea comes with its own healthy and normal endothelium. Thus, once the donor cornea is healed, the endothelial function is restored and the cornea becomes transparent. Clear vision is recovered. There is a 95% success rate for corneal transplant surgery for this condition.