Michael Baertschi, MSc Mmed Education FAAO
Michael Wyss, MSc FAAO
Simon Bolli, Eidg dipl Augenoptiker
Marc Fankhauser, Eidg dipl Augenoptiker
Fitting (R)GPs after penetrating keratoplasty (PKP) can be a challenge. Small overall diameter lenses would be easier to fit, but an irregular graft and host interface often results in a dislocated contact lens and patient discomfort. FItting a bigger diameter lens on the peripheral host-cornea offers the possibility of an incredibly comfortable and stable contact lens on the eye. Keep in mind that central keratometry readings do not have any relationship with the peripheral curvature of the host cornea. This article will focus on peripheral fitting possibilities, such as peripheral-toric and quadrant-specific designs, combined with reverse geometry in PKP cases.
A 41-year-old female underwent PKP a few years ago and was fitted with a single curve (R)GP corneal lens. She complained about halos, marked discomfort and frequent lens loss (Figure 1).
Figure 1: Patient’s dislocated single curve (R)GP Design
According to the Pentacam (Scheimpflug) height measurement, there is a substantial amount of toricity on the peripheral host cornea (Figure 2).
Figure 2: Elevation mapping, note the high difference in height between the vertical and horizontal meridian.
Additionally, the cornea seems to be steeper inferiorly than it is superiorly. After the first diagnostic (R)GP lens with a “simple” peripheral-toric lens design, a quadrant-specific lens design was chosen because of the inferior edge lift-off. Also, the peripheral-toric lens rotated on the eye, creating an unstable lens.
Figure 3: Peripheral-toric lens design, note the dramatic inferior edge lift
The final lens ordered had a 10.60mm diameter in a reverse geometry design with a quadrant-specific component. The numeric eccentricity values (nE) in the horizontal direction were 08 / 08, while superiorly they were 06 and inferiorly 04. Due to the different e-values in each quadrant, the lens perfectly fits into the curvature of the host cornea.
The fluorescein pattern showed the typical reverse curve pattern, peripheral alignment, adequate sagittal depth and overall a much better centration of the lens (Figure 4).
Figure 4: Reverse Geometry and quadrant-specific periphery (red numbers = nE)
Subjectively, the contact lens could be tolerated much better now, no halos were seen, and no loss of lenses has been reported to date.
Reverse geometry lenses offer a fascinating approach for fitting (R)GPs after PKP. However, for better comfort and centration, alignment fitting of the peripheral host-cornea is critical. Sometimes more complicated geometries, such as peripheral-toric or quadrant -pecific lens designs, are needed to succeed. Once the lens periphery is fitted with alignment, comfort and vision will increase dramatically. Our next I-site Newsletter contribution will focus on fitting corneas that have tilted or off-center grafts.
Michael Baertschi was the senior optometrist at the University Eyehospital Basel from 2000 to 2007. He is the owner of Kontaktlinsenstudio Baertschi in Bern, Switzerland and the CEO of Eyeness AG in Bern. Michael graduated from Pennsylvania College of Optometry as M.Sc. Optom. and from the University of Bern as M.med. Educ. Michael Baertschi is a fellow of the American Academy of Optometry and president of the Swiss Interlens group.
Michael graduated from Olten SHFA in Switzerland and did his MSc at the Hochschule Aalen Germany (in cooperation with New England College of Optometry and Pacific University, USA). Since 1999 he has worked in a private practice (kontaktlinsenstudio Baertschi in Bern, Switzerland) as Optometrist for specialty contact lens fitting. Additionally, he is an adjunct Faculty Member at the New England College of Optometry USA, Hochschule Aalen Germany, TVCI in Prague (Czech Republic) and FHNW Optometry in Olten Switzerland. Michael is a clinical investigator for several Industry Partners and has published or lectured on several topics in the contact lens field throughout the world. Michael is a Fellow of the American Academy of Optometry and serves as a the vice chairman of the Admittance Committee for new Fellows outside the USA.