Advanced Techniques
Keratoconus

Treatment With Contact Lenses

Keratoconus may be successfully treated with contact lenses. The purpose of the lens is to cover the irregular astigmatism created by the distorted anterior surface of the cornea. The tear layer found between back surface of the contact lens and the front surface of the cornea serves to fill in the corneal irregularities thereby providing a smooth optical surface. Rigid lenses are far more effective at accomplishing this purpose than are soft lenses. Contact lenses do not retard the progression of the disease nor do they provide a cure, although the patient may experience long periods of natural remission. Successful fitting requires a combination of patience, diplomacy, and a great deal of skill. Spectacles are only helpful in early, mild cases.

Three-point fit apical touch to the cone plus peripheral touch. Ideal for keratconus because of the distribution of weight of the lens,

Flat fit-apical touch but poor centration because of rocking on the corneal cap and edge standoff.

 

Steep fit two-point touch with an air bubble between the lens and the cone. The apical cone is cleared.

 

The keratoconis patient may be fit using one of the following approaches:

Single Cut Lenses: In the ideal fit, these lenses will touch the apical cone lightly and come to rest on the peripheral cornea in an area where there is little or no thinning. Lenses fit excessively flat may cause corneal abrasions. Lenses fit too steep to cause even minimal apecal clearance will result in the pooling of tears around the periphery of the cone. The pooling of tears can result in discomfort, hazing and bubble formation.

Soper Keratoconus Diagnostic Fitting Set: These lenses are designed with a steep base curve to accommodate the steep central cone area with a much flatter peripheral curve to rest on the surrounding cornea. It is essential to use a trial set containing base curves of 48.00 D to 60.00 D when fitting these lenses. The lens diameters range from 7.5 to 9.5 mm. A good fitting lens would show the following: apical clearance with circulation of tears between the apex of the cornea and the back of the lens, good centration, and some movement of the lens with blinking.

Thin Lens: These are sometimes referred to as Dura-T-Lenses. The key element in their design is that they are made thinner with a center thickness of about 0.08 mm. The reduced mass also reduces the lens weight by about 30% and assists in centration and patient tolerance.

Soft (Hydrophyllic) Lenses: They are useful for the keratoconus patient who cannot tolerate a rigid lens. They are fit with a relatively flat base curve 8.1 to 8.4 mm and a fairly large diameter 13 to 14 mm in order to provide lens stability. While soft lenses don�t normally mask astigmatism, they have been shown to reduce a significant amount so that overcorrection with spectacle lenses becomes effective.

Piggyback Lenses: These are used when the patient cannot tolerate rigid contact lenses and when the use of auxiliary spectacles needs to be avoided. A soft lens of about 14 mm in diameter is placed on the cornea. A rigid lens is placed over it which may ride freely or be placed in a depression in the soft lens designed to hold the rigid lens in place. The diameter of the rigid lens usually ranges from 8.5 to 9.5 mm.

 

Extending the Range of the Keratometer

The range of the keratometer may be extended in the steeper range by placing a +1.25 D lens over the aperture. It may be extended in the flattser range by placing a -1.00 D lens over the aperture.