How Should I Approach the Fitting of My Post-Penetrating
The post-penetrating keratoplasty (PK) patient can be particularly challenging, due to the amount and irregularity of the cornea. Certainly many of the same tools recommended for keratoconus patients would be indicated here. A larger diameter than that used for healthy corneas is typically standard in these cases, often in the 10-11mm range.
One philosophy from GPLI Advisory Committee member Loretta Szczotka-Flynn, OD, PhD, is based upon Waring’s five post-PK shapes:
- Prolate cornea
- Oblate cornea
- Mixed (oblate and prolate)
- Asymmetric cornea
- Steep-to-flat cornea
- Prolate cornea. This can simulate normal aspheric corneas, and a keratoconic GP design is often successful in these cases.
- Oblate cornea. This is a flat central topography with a steep periphery (or some variant of this pattern). A reverse-geometry lens design with a secondary curve radius steeper than the base curve radius by an amount less than or equal to the dioptric transition change from flat to steep regions.
- Mixed. These topographies often look fairly symmetrical, with one meridian being much flatter than the other meridian. Therefore, a bitoric GP design is often successful.
- Asymmetric cornea. An intralimbal design can be used initially with these patients, but the asymmetry of the corneal topography often necessitates a scleral lens design.
- Steep-to-flat cornea. A tilted graft or an excessively steep region above, below, or lateral to an excessively flat region often necessitates either a scleral design or a quadrant-specific design to align better with a cornea having two dramatically different curvatures.
In general, a careful analysis of the topography needs to be made to determine the optimal lens design. Frequently, a highly toric central cornea can be fit easily with a larger spherical lens design.
Use of trial lenses to evaluate the fit and design needed is also important.
GP Lens Institute/Scleral Lens Education Society
- Jedlicka J. Solving Scleral Lens Complications.
- Bennett E.S., Sonsino J., Anderson B. 20 Pearls for Managing Post-PK Patients with GP Lenses, Part 1.
- Bennett E.S., Grohe R., Edmonds S. 20 Pearls for Managing Post-PK Patients with GP Lenses, Part 2.
- Bennett E.S., Brown M., Anderson B. 20 Pearls for Managing Post-PK Patients with GP Lenses, Part 3.
- Szczotka-Flynn L. Fitting Contact Lenses After a Corneal Transplant.
GP Lens Institute Advisory Committee members: Bruce Anderson OD, Marlane Brown OD, Carmen Castellano OD, Walter Choate OD, S. Barry Eiden OD, John Laurent OD, PhD, Derek Louie, OD, MS, Joe Shovlin OD, Frank Weinstock MD, Bruce Williams OD.