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Using Plus Powered Silicone Hydrogel Lenses for Piggyback Lens Fitting
Provided by
Timothy A. Giles, OD Global Head, Professional Services – Specialty Lenses
Case Report
A 36-year-old male was referred for complicated lens fitting following penetrating keratoplasty (PK) in his left eye. He had previously undergone PK with a running suture. He was referred to our center after several unsuccessful attempts of rigid gas permeable (RGP) lens fittings. According to the data from his surgeon’s office, standard and reverse geometry RGP lens designs were attempted but failed. When I first saw this patient, the RGP lenses were riding very low on the lower limbus and central bubbles were noted. The patient was intolerant to the RGPs and he often reported the lens falling out of his eye after only 1 hour of wearing time. Since his right eye had recently been worsening from progressing Fuch’s dystrophy, he wanted to try something for the left eye now, rather than wait for the right eye to be in the same situation. Since the sutures were being removed in four days, I elected to evaluate this patient for contact lenses after removal of the sutures.
At the subsequent visit after suture removal, his left eye had these findings:
Manifest Refraction: +7.00 -3.25 x 035 20/40-
Simulated Keratometry: 38.62 @ 126 / 34.12 @ 036
Biomicroscopy: graft clear, apparent elevated wound tissue, which was confirmed by topography.
The graft was irregular, excessively flat and depressed. My approach in dealing with these irregular corneas is to change the graft contour by using a soft contact lens / RGP piggyback system.
In this case with a flat cornea, the initial soft lens chosen was a +6.00 8.6 lotrafilcon A (NIGHT & DAY). The topography over this soft lens was repeated which revealed steepening centrally and an improved fitting surface for the RGP. The RGP diagnostic lens fit over the soft lens was:
Visions Ultrathin (Paragon HDS): Diam 9.3mm, BC 7.71mm, OZ 8.7, power +2.00. This resulted in an over-refraction of: -0.50 -1.00 x 020 (20/25).
The lens exhibited central corneal clearance, good centration, no edge lift and the patient reported significantly improved comfort. (see Figure 1)
Figure 1
The following changes were made to the piggyback lens system:
Soft lens:
8.6 +6.00 lotrafilcon A (NIGHT & DAY)
RGP:
7.71 / 9.3 Visions Ultrathin +1.50 with 8.7 OZ.
This patient was satisfied with the vision and comfort of the piggyback system. He felt confident this system would establish some stability to his left eye as he awaited the decision on his right eye.
Discussion
Fitting irregular corneas is challenging, and standard RGP designs are not always effective. Of particular challenge is the oblate cornea which is often associated with post-PK, post-RK and post-LASIK. Soft lenses have limited vision correction potential for these irregular corneas. Even with low astigmatism, low Dk lenses are avoided due to the diminished oxygen transmission. Silicone hydrogel lenses are preferred but still remain limited in their parameters (Rx, diameter and BC). With the introduction of made-to-order silicone hydrogel lenses from CIBA Vision, the use of high Dk lenses with extreme parameters will allow more freedom and flexibility in fitting piggyback lenses.
Conclusion
In summary, I had success using silicone hydrogel soft contact lenses to improve the corneal fitting surface thereby improving the RGP lens fit in a piggyback system. If the cornea is relatively flat, a high plus silicone hydrogel soft lens in combination with a RGP piggyback often works well. In situations where the host inferior cornea is relatively steep, the use of a high minus lens will usually improve the fitting surface of the cornea, thereby improving the RGP fit in a piggyback design. |
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