scleral contact lenses
"What Are They Like"?
Gas-Permeable scleral contact lenses are larger than
conventional contacts. They vault over and cover the
cornea (black central "window" area of the
eye) and ride over the sclera (white tunica outer
strong protective coating of the eye) upon which the
lens sits, thus allowing tears to occupy the space
between the lens and eye. The lens edges extend underneath
the eyelids; therefore sclerals can feel very comfortable
from the outset. Resting on the sclera provides for
great stability and uniformity of vision.
How Do The Lenses Work And Why?
The use of Perspex (plastic) for the manufacture
of scleral contact lenses although a great step forward
prevented the passage of oxygen and carbon dioxide
through the lens surface, so that the "eye"
underneath could not respire (breathe) sufficiently
for them to be worn for long periods. This was improved
by drilling fenestrations (holes) in the lens surface.
This procedure caused the introduction of bubbles
underneath the lenses in the tear layer and also allowed
them to settle back onto the eyes
Diagram shows a cross section
of eye with gas
permeable contact lens supporting full tear
around and between lens and irregular front
surface of eye.
surface - as a building with poor foundations would
on soft soil. Reworking the lens back surface allowed
for an increased liquid lens between the eye and lens
and the possibility of larger bubbles to form. The
Perspex surface was also hydrophobic (water repellent)
thus tears were unable to "wet" its surface.
New Materials And Methods Give Better Results
The advent of different gas-permeable plastics from
a base of Fluorine and Silicone has allowed great
strides to be made. The plastics are fully wettable
by tears and also extremely permeable to dissolved
Oxygen and Carbon dioxide over their whole surface,
thus obviating the need for Fenestration. Thus bubble
formation is invariably absent as is the problem of
Principle Of Working On Irregular/Damaged Front
As the lens vaults the central corneal area the space
is filled with tears any form of front surface corneal
irregularity or indeed damage is fully immersed with
them. These tears also wet and adhere to front and
back surfaces of the lens, thus the front surface
of the scleral contact lens become the "new"
artificial front of the eye. This surface can be made
to incorporate the eye power and as it is smooth,
regular and fully wetted and cleaned by regular blinking
can provide excellent vision on damaged corneas. This
continuously interchangeable natural tear layer is
the basis of the success of the gas-permeable scleral
contact lenses as the eye is able to respond again
with the outer surface intact and smooth, provided
by the lens surface.