What is Fuchs’ Dystrophy and why is the cornea swollen?
Fuchs’ Dystrophy was described by Dr. Fuchs over 100 years ago. It is a genetic condition which selectively affects only the endothelial layer of the cornea. It has a very wide spectrum of affect, with most Fuchs’ patients never experiencing any visual problems and completely unaware that they even have the disease. Of those patients that have severe forms of Fuchs’ Dystrophy, the average age of corneal transplantation is about 70 years old. However, there are some patients that need surgery as early as 40 years old and others that do not need it until they are over 90 years old. The time for corneal transplant surgery is wholly dictated by how difficult the vision is for the patient for their normal activities of daily living…and that is different for different people.
For the normal genetic individual, when we are born, we have about 6,000 endothelial cells for every square millimeter of the back of the cornea. As we age, we slowly lose these cells over time, and they are not replaced. (Endothelial cells do not multiply). By the time we are 50 years old, we have about 3,000 cells left. By the time we are 80 years old, we have about 2,000 cells left. By the time we are 100 years old, we have about 1500 cells left. (after 100 years old, who knows?!) The question comes up: How many cells do I need to keep my cornea clear?...you only need about 400 to 500 cells per square millimeter. So the natural loss of endothelial cells over time is very well tolerated.
In Fuchs’ Dystrophy, the individual is still born with 6,000 cells but those cells are abnormal and die off at an accelerated rate. So the Fuchs patient may have only 1,000 cells at the age of 50 years old and only 500 cells at the age of 65 years old. As the number of cells gets below 1,000, there begins to be signs of corneal fluid retention that we can measure as an increase in corneal thickness. As the endothelial cell count progressively gets lower, the patient may start to notice changes in the vision such as reduced “cloudy” or “blurry” vision that is present when awakening, but gets better after being awake for an hour or more. In severe cases of Fuchs dystrophy, there is such a severe loss of endothelial cells and therefore “pumps”, that the corneal swelling is severe, causing little water blisters to form on the surface of the cornea (epithelial fluid cysts, or “bullae”). When this happens, the patient notices a precipitous and severe drop in vision, almost like he/she is looking through “bubble wrap”. Over time, the blisters get bigger and bigger, and if left unattended, the epithelial blister eventually break down, expose the corneal nerves, and cause severe pain for the patient. Finally, the natural course of the disease is to have the chronic blistering cause tissue scar formation on the surface. This helps to relieve the chronic pain, but leave the patient with a permanent scar and poor vision which can only be treated with a full thickness corneal transplant (and NOT a selective DLEK or DSEK endothelial transplant).
The is also a higher incidence of early cataract formation in patients with Fuchs’ dystrophy. A cataract means that the focusing lens inside the eye turns cloudy. This is why many patients with Fuchs’ dystrophy will also require cataract surgery at the same time as their corneal transplant. In addition, the steroid drops that are used after corneal transplant surgery to keep the donor cornea from rejecting can also have the side effect of causing or accelerating the development of cataracts.