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Fitting a Bitoric RGP Cornea1 Lens

Joe B. Goldberg, OD, FAA0

A bitoric rigid gas permeable (RGP) comeal lens may appear to satisfy fitting criteria when it corrects vision to normal levels and the patient is comfortable (Figure 1).

However, observing the fit when the tears are stained with fluorescein will furnish a better description of the lens- to-cornea fitting relationship (Figure 2).

The patient was fitted with a bitoric RGP cornea1 lens whose toric ocular surface was designed according to a method previously reported. ’ Vision was corrected to 20/ 20, the lens was comfortable, but there was apical clearance and peripheral bearing. The existing lens was modified to reduce the central sagittal depth and minimize the para-

Figure 2. Apical clearance and para-apical cornea1 bearing.

Figure 1. A bitoric RGP comeal lens fit observed in white light.

Address reprint requests to Dr. Goldberg at 4217 Virginia Beach Blvd., Virginia Beach, VA 23452.

Accepted for publication August 1990. Figure 3. Reduction in sagittal depth when the optic zone diam- eter was made smaller.

300 ICLC, Vol. 17, November/December 1990 0 1990 Butterworth-Heinemann

Figure 4. An alignment fit of a bitoric RGP comeal lens.

Fitting a Bitonic RGP Comeal Lens: Goldberg

apical bearing areas. The optic zone diameter (or chord diameter of the base curve) was made 0.5 mm smaller. Although this reduced the sagittal depth to some degree, it did not eliminate the para-apical bearing areas, (Figure 3).

Consequently, a new bitoric RGP cornea1 lens was made. Making the toric ocular surface 0.05 mm flatter in each meridian and retaining the modified optic zone diam- eter and the overall lens size eliminated the para-apical comeal bearing, (Figure 4). Changing the base curve radii dictated a need to modify the spherical power (it was nec- essary to decrease the minus power 0.25 D), but not the cylindrical power.

Reference

1. Goldberg JB: Designing RGP toric and bitoric comeal lenses. Contact Lens Forum July, 1986;27-30.

ICLC, Vol. 17, November/December 1990 301