Although there are over twenty different corneal dystrophies, most have
these features in common: dystrophies 1) are usually inherited, 2) affect
the right and left eyes more or less equally, and 3) are not caused by
outside factors such as injury, activity, or diet. Dystrophies have
other similarities: 4) most start gradually and get worse gradually, 5) most
usually begin in just one of the five corneal layers and later spread to
nearby layers, 6) most are not in any way related to diseases affecting
other parts of the eye or the rest of the body, and 7) most can occur in
otherwise totally healthy persons of either sex.
Corneal dystrophies can affect
persons of all ages, but each dystrophy has a characteristic time of life
when it is first noticed by patients or their ophthalmologists. For
example, the dystrophy keratoconus often affects patients in their teens and
20's; another common dystrophy, called Fuchs' dystrophy, typically is not
noticed until patients are in their 50's and 60's.
Almost all of the corneal
dystrophies are inherited in a way that is called autosomal dominant.
Autosomal means that male and female children of a person with a dystrophy
are equally at risk of inheriting the dystrophy. Dominant in this
Instance means that It Is likely that one of the patient's parents has the
dystrophy and that each and every offspring of the patient has one chance In
two of inheriting the dystrophy. Unfortunately, at present there Is no
way of predicting before birth whether or not a child will be affected.
A few corneal dystrophies have
different means of inheritance. Keratoconus and macular dystrophy are
two of these; their means of Inheritance will be explained in the separate
books dealing with each of them.
Often not all family members
with the dystrophy have equally severe forms of it. To give an extreme
example, one person with dystrophy might lose useful vision so that he needs
a corneal transplant by age 20, whereas his sister who has the dystrophy
might see well until she Is In her 30's or 40's. What controls this
variability of severity In a family is not known.
Corneal dystrophies affect
vision in widely differing ways. A few cause no vision problems at all
and are only incidentally discovered during a routine eye examination.
Others cause repeated episodes
of eye pain without leading to permanent loss of vision; these dystrophies
usually affect the epithelium (layer 1) or its basement membrane. The
epithelium does not stick properly to the basement membrane, so that normal
actions, such as blinking or s1eeping, can make epithelial cells peel off.
This is called an epithelial abrasion or erosion. (See Fig. 1) It
produces the painful foreign-body sensation that we described In Section 1.
The most common time for patients to get an epithelial erosion in this way
is overnight, so that the patient first notices It on awakening in the
Treatment is readily available
for epithelial erosions when they occur; your ophthalmologist will probably
treat you with drops, ointment, and/or an eye patch. (See Fig. 2) With treatment,
these erosions usually heal within 1-3 days. Unfortunately, in many
patients these erosions occur repeatedly; this problem is called recurrent
erosion. In patients with some corneal dystrophies, the erosion can
occur quite frequently and can be a problem for many' months or even a few
years; in others, the erosions occur infrequently and are much less
bothersome. Recurrent erosions can sometimes be prevented through the
use of drops, ointment, or even a soft contact lens.
In some other dystrophies,
severe loss of vision often occurs from either dense corneal clouding or
roughening of the corneal surface. Some of these dystrophies also
cause episodes of foreign-body sensation from recurrent erosions, as we just
discussed. Many patients who have dystrophies in this group will
eventually require corneal transplantation in order to see well again. (See
Fig. 3.) Fortunately, corneal transplantation is very often
successful for them and enables them to resume full, active lives.