Progression of Fuchs
The development of Fuchs can be separated into stages, each of which normally last ten to twenty years. Though there may be slight differences at the cellular level, most cases of Fuchs Dystrophy follow similar patterns during the progression of the disease.
Guttae: Bumps on the back surface of the cornea. These appear before the patient experiences symptoms.
The Krachmer Scale
In 1979, Dr. Jay Krachmer and his colleagues proposed a scale for grading Fuchs Dystrophy. It goes from levels 0 through 5. Their system was meant to make it easier for doctors and researchers to communicate regarding the about the condition of a patient’s eyes.
The Krachmer Grading Scale
No apparent disease.
|Definitive onset of the disease.|
Twelve or more central,
nonconfluent guttae in at least one
|A zone of confluent central guttae 1 to 2 mm in horizontal width.|
|A zone of confluent central guttae 2 to 5 mm wide.|
|A zone of confluent central guttae greater than 5 mm wide.|
|A zone of confluent central guttae greater than 5 mm wide plus edema of the corneal stroma and/or corneal epithelium.|
|Grade 5||Grade 5||Grade 5|
Researchers at the Wilmer Eye Institute have recently published a scientific paper detailing how retroillumination photographs (such as those in the table above,) can be used to analyze the progression of Fuchs. You can read that paper by clicking here.
General Progression of Fuchs
In the first stage of the disease, Descemet’s membrane thickens, leading to excrescences or bumps called guttae. Some endothelial cells begin to lose their regular hexagonal form, and increase in size (polymorphisms), with irregular shape (polymegethisms), resulting in inefficient endothelial function.
|Note that select cells have lost their hexagonal shape. The lighter circles are the beginning of guttae.|
Image from the collection of John D. Gottsch, MD
In the beginning stages of FECD, symptoms include dry eyes, and eglare and cloudiness can occur. The damaged endothelium can lead to accumulations of fluid in the stroma and epithelium. Increased swelling (edema) causes the stroma to thicken.
In advanced stages of FECD, pockets of fluid can accumulate beneath the epithelium. These pockets of fluid are known as bullae. Enlargement of the stroma causes some areas of Descemet's membrane to fold. Improved vision no longer returns as the day progresses, and painful sensations emerge.
The final stage of Fuchs is characterized by loss of most endothelial cells and gross thickening of Decemet’s membrane. Corneal scarring can occur with heterogeneous, dense, avascular tissue between the epithelial layer and Bowman's layer. This late stage of FCD results in marked loss of vision.
Corneal tissue normally regenerates from what are called limbic stem cells. These are located around the perimeter of the cornea. Corneal tissue that regenerates from the central part of the cornea (as in the final stages of FCD,) does not look or act like real corneal tissue. Corneal tissue must be clear in order for you to see through it. In addition, it must be dome-like and smooth, without any bumps or pulls in it. Both of these aspects of corneal function are compromised when the tissue is formed from cells from the center of the cornea.