< Page 2 of 14 >

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Fitting & Verification
Rigid Lenses


Two broad categories of rigid contact lenses would include the Palpebral Lens and the larger Lid Attachment Lens.

THE PALPEBRAL 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.

Advantages:

  1. It provides excellent tear exchange resulting in minimal corneal edema and spectacle blur.

  2. Eye movement is free from lid irritation since the lens is smaller than the palpebral fissure.

  3. 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.

  4. A high riding rigid lens problem may be solved through the use of the small microthin lenses which may center better

  5. Patients who have induced corneal astigmatism caused by the �mold- ing� effect of larger lenses may benefit from a
    smaller microthin lens.

Disadvantages:

  1. The interpalpebral lens should not be used where the lens is likely to be high riding, such as in severe myopia. Their thinness can actually carry the lenses higher.

  2. They can be difficult to remove. Their thin edge makes it difficult for the upper lid to dislodge the lens.

  3. In cases of high corneal astigmatism, they don�t center particularly well.

  4. They warp relatively easily, are difficult to modify because of their size, ` and because of their thinness, they are easier to damage or break in handling.

  5. Patients with large pupils often complain of �flare.�

< Page 2 of 14 >

1 2 3 4 5 6 7 8 9 10 11 12 13 14