The white part of the eye is called the
sclera and these lenses are designed to vault the cornea and be
supported by the sclera with a fluid reservoir between the cornea and
the contact lens. The smallest of these lenses will cover the entire
colored part of the eye and will then extend a small amount onto the
white part of the eye. The largest of these lenses will continue to
extend onto the white of the eye so that every part of the eye that is
showing, and even some parts that are hidden by the lids, will be
covered by this lens.
Only the more oxygen-porous gas permeable materials are used to ensure
an adequate supply of oxygen for the cornea. Handling the lenses is
rather easy since they are so large, but application and removal of the
lenses to and from the eye can be a bit trickier than conventional
contact lens designs. The materials chosen are generally clear. This is
because a lens with color will show on the white part of the eye which
for most people is cosmetically undesirable.
The fitting process as well as the manufacturing process is quite a bit
more challenging with this class of lenses. This fact along with the
fact that mass-production of these types of lenses is not possible,
means that their costs can be significantly higher than the traditional
contact lenses of today. There is also more time required when fitting
them. This means more time for the physician, more time for the patient,
and more time for the laboratory actually manufacturing the product.
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Due to all of the above reasons, scleral lenses are not utilized
in a routine fashion. These very unique products however, do
have their place. For corneas that have become irregular,
scleral lenses can sometimes outperform other types of contact
lenses. An irregular cornea can be the result of a disease such
as Keratoconus, corneal trauma, corneal transplant, and more
recently refractive surgery. In many cases, the irregular cornea
prevents the proper positioning of a corneal lens but a scleral
lens can seat itself properly on the sclera and therefore be in
the correct position on the cornea. The vision with a scleral
lens as well as the other gas permeable corneal lenses can be
vastly superior to glasses or soft contact lenses
when considering irregular corneas. These lenses provide the
optical system a new surface that provides great vision while
neutralizing all of the irregular optics of the underlying
cornea. For many people with irregularly shaped corneas, these
types of lenses provide the only form of usable vision
correction.
Additionally, scleral lenses can address many contact lens
failures that were secondary to dryness. Since the scleral
lenses are so large, there forms a tear reservoir under the lens
that can keep the cornea properly moist. Foreign matter and
debris also have a very difficult time finding their way
underneath one of these lenses. This fact can be the single
entity that allows this lens success while other contact
lenses fail.
Whenever I show a scleral lens to a patient for the first time
the patient’s reactions are almost always the same. The comment
is always something to the effect “Are you planning on putting
that huge thing in my eye?!” This is followed with “How much is
it going to hurt?” The surprising and good news is that the
scleral lenses are extremely comfortable right from the
beginning. Due to their size, contour, and limited movement,
there is actually very little sensation at all. |
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