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Gas-Permeable 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

ross section of eye with gas
Diagram shows a cross section of eye with gas
permeable contact lens supporting full tear layer
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 settling.

Principle Of Working On Irregular/Damaged Front Corneal Surfaces

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.

 

 

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