Keratoconus is an abnormal condition of the cornea, the clear dome over the
pupil, in which the center bulges forward in the shape of a cone, compared to
the normal spherical shape.
The condition has been said to be hereditary, but there are few families in
which there is more than one person with it. It usually begins in the late teens
or early twenties and progresses, but usually stabilizes and rarely becomes
worse after the forties or fifties.
Keratoconus disturbs the vision because the front surface of the cornea is not
a smooth, regular refracting surface. The cornea must be smooth, spherical
and regular to provide sharp, clear vision.
Early keratoconus manifests itself as mild and, later, severe astigmatism.
Astigmatism is a condition in which the cornea is curved slightly like the side
of a football with two different curves. The normal cornea is spherical like the
shape of the side of a basketball. A spherical or slightly astigmatic cornea is
necessary for sharp, clear vision. Early keratoconus can usually be treated
with spectacles to provide good vision.
As keratoconus progresses, the center of the cornea bulges forward, roughly
in the shape of a cone, or more like the end of a football. The corneal surface
is no longer spherical and vision cannot be corrected with glasses. Rigid
contact lenses can be fitted to correct the vision and provide normal eyesight.
The backside of a rigid contact lens covers up the irregular surface of the
keratoconus cornea, while the front surface provides a smooth, spherical
refractive surface to allow for sharp, clear vision.
As the condition advances, fitting of the contact lens to the irregular cone-
shaped cornea can become a challenge. There are several special designs
of back curved lenses to accommodate the different shapes of keratoconus
corneas.
Fitting of keratoconus contact lenses is a challenge and may require the
design and ordering of several different contact lenses to reach the final well-
fitting lens that can provide good vision. Thus, a new lens may not fit perfectly
or provide good vision, but may be necessary to learn how to design the next
lens. It is discouraging for the patient and the doctor for a new contact lens to
have poor fitting characteristics and fail to provide good vision. Keratoconus
contact lens fitting can be expensive because of the many lenses needed to
finally reach the desired lens shape and power to provide comfort and good
vision.
If the corneal cone advances sufficiently so that good vision and lens comfort
are not possible, corneal transplant surgery may be necessary. A circular
center corneal section is removed and a donor cornea is sutured into the
same location. Healing takes about a year. Good vision may then be
possible with glasses or a special contact lens may be necessary to provide
good vision.
Why not do corneal transplant surgeries early in the condition? Some
aggressive surgeons do just that. Other surgeons feel that only five to ten
percent ever really need surgery.
What is the downside of corneal transplant surgery? In the first place, it is
surgery. It is usually very successful surgery, yet it carries with it the risks of
surgery. After surgery, the cornea never really heals solidly. The cornea has
no blood vessels. Scar tissue that occurs in skin and other parts of the body
to heal solidly cannot occur in the cornea. The cornea is never as strong after
cornea transplant surgery. Contact sports should not be in the future of people
who have had corneal transplants, because the cornea is not as strong.
What about the future of people with keratoconus? It can be discouraging for
a young person to learn he or she has keratoconus. Experience indicates that
the future should be quite bright. It is a bother to have to comply with contact
lens fittings and to take care of the contacts. Experience with keratoconus
patients indicates that they do very well.
What is the cause of keratoconus? The cause has never been definitely
determined. The problem seems to be in the center part of the cornea, called
the stroma. The stroma is made up of interlacing, clear fibers. Why does the
stroma become weak and allow the cornea to bulge forward?
Dr Fredrick Ridley presented a lecture in Houston, Texas in 1966 and
reported on 1800 cases of keratoconus from all over the British Empire that
he had treated with contact lenses. He had noticed that most of the patients
were “eye rubbers” because of allergies, and attributed this as the cause. He
noted that some are “eye gougers” and really rub their eyes vigorously with
their knuckles.
The allergy theory as a cause of keratoconus has been discussed in many
medical articles. The theory considers that the rubbing causes increased
pressure in the eye and forces the cornea to bulge and become distorted due
to some unknown weakness in the center part of the cornea, called the
stroma. Why is the stroma weakened? Could it be related to some as yet
unknown effect of allergy?
Other questions are unanswered. Is there an inherent weakness of the cornea
due to heredity? Could the cornea be weakened from some nutritional
deficiency? The cornea has no blood vessels to receive nutrition, as do most
other organs. It receives most of its nutrition and some of its oxygen from a
clear fluid that bathes the backside of the cornea, called aqueous humor.
Among the many nutrients are vitamin C concentrations, ten to thirty times
greater than in the blood. Vitamin C enters the aqueous humor in its oxidized
form. After giving up its oxygen to the cornea, lens, and other surrounding
structures, it re-enters the blood stream in its reduced or unoxidized form and
is rapidly excreted by the kidneys in four to six hours. Thus, vitamin C requires
nutritional replacement several times daily. Vitamin C is necessary for the
production of collagen, a fibrous protein that is the “glue” that holds tissues
together and contributes to tissue stability. The cornea contains collagen.
Could failure to eat enough fruits and vegetables, which contain vitamin C,
result in weakness of the cornea and result in keratoconus? Of course, many
youth do not eat enough fruits and vegetables and only a few develop
keratoconus. Could a hereditary tendency or inherited tendency to have
allergies contribute to susceptibility of the cornea to weakness and result in
keratoconus? Could some people fail to absorb an adequate amount of
vitamin C from their diets?
There are many questions as to the cause of keratoconus. The good news is
that it can be treated successfully and those with it can have normal lives.
