Two broad categories of rigid contact lenses would include the Palpebral Lens and the larger Lid Attachment Lens.
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THE PALBEBRAL LENS:
General characteristics: The lenses are small and thin.
They are small enough to be contained within the
cornea with little or no contact with the upper or lower
lids. Diameters usually range from 7.8 to 8.6 mm. With
each blink the lens moves up and approaches the
superior limbus. Between blinks, in ideal cases, it falls
slowly toward the inferior limbus lowering to just
below the center. Thicknesses are generally in the range
of 0.08 and 0.12 mm. and the peripheral curves are
relatively steep.
The lenses should be large enough to provide a minimal
sense of motion during blinking producing as little
glare as possible. However, too large a lens can result
in reduced comfort. The thinness of the lens results in
some flexure with each blink which creates a tear pump
that can help with tear exchange.
- It provides excellent tear exchange resulting in minimal corneal edema and spectacle blur.
- Eye movement is free from lid irritation since the lens is smaller than the palpebral fissure.
- The thinner lenses are more comfortable than conventional lenses and can therefore be employed as a possible alternative to soft lenses especially when a significant amount of corneal astigmatism is present.
- A high riding rigid lens problem may be solved through the use of the small microthin lenses which may center better.
- Patients who have induced corneal astigmatism caused by the the "molding" effect of larger lenses may benefit from a smaller microthin lens.
