contact lens case reports
A Reverse Geometry
Lens for Post-RK Patients
BY PATRICK J. CAROLINE,
FCLSA, FAAO, & MARK P. ANDRÉ, FCLSA, FAAO
The two major concerns when using soft lenses
after radial keratonomy are corneal neovascularization at the site of the incisions and excessive lens vaulting over the flattened central cornea.
Historically, selecting a higher Dk lens material and optimizing the lens fit through appropriate base curve/diameter selection can lessen neovascularization.
Today, excessive apical clearance can now be managed with a unique custom soft lens design from Innovations in Sight (Front Royal, VA). This lens incorporates a posterior reverse geometry configuration similar to that described by Fontana in 1972.
Patient VB is a 45-year-old female who underwent bilateral radial keratonomy in 1989 (Figure 1). Today her manifest refraction is OD +6.75 sph. 20/40, OS +5.50 sph. 20/40. Keratometric readings were OD 35.00 @ 46/36.00 @ 136 (+2 distortion) and OS 36.50 @ 90/36.87 @ 180 (+2 distortion) (Figure 2). The patient has made several unsuccessful attempts to wear RGP and soft lenses over the past five years and was currently wearing spectacles.
|Figure 1. Patient VB OD (left) OS (right).
||Figure 2. Videokeratography
The patient was fit with the new reverse geometry soft lens design (Figure 3) to avoid the vaulting effect that occurs with traditional lenses on post-refractive surgery corneas. Figures 4 and 5 show the change in topography with the soft lens vs. without it.
|Figure 3. New reverse geometry SCLs
||Figure 4. Photokeratoscopy OD: without SCL (left) with SCL (right).
The lenses were manufactured with two curves on the posterior lens surface, a flatter 9.70mm radius centrally and a steeper (more normal) 8.60mm radius mid-peripherally. Final lens powers were OD +5.50D and OS +4.75D with a 15.0mm diameter. The anterior surface was aspheric to reduce the aberrations created by the post-refractive surgery topography. Our patient's final VAs were exceptionally stable at 20/25 -2 OD and 20/20 -1 OS with comfortable, all-day lens wear.
Figure 5. Photokeratoscopy OS: without SCL (left) with SCL
Patrick Caroline is an associate professor of optometry at Pacific University and an assistant professor of ophthalmology at the Oregon Health Sciences University.
Mark André is
director of contact lens services at the Oregon Health Sciences University.
Contact Lens Spectrum, Issue: January 2002