contact lens case reports
Fitting a Reverse Geometry Lens on a Post-LASIK Patient
BY PATRICK J. CAROLINE, FAAO, & MARK P. ANDRÉ, FAAO
Since 1997, more than one million LASIK procedures have been performed annually in the United States. While surgical outcomes have greatly improved, the nature of ocular surgery has left in itsits wake patients for whom contact lenses may be their best means for visual correction and restoration of binocular vision.
The ultimate success of any GP lens (regardless of its design) depends on three fitting criteria:
- The base curve radius must clear the apex of the cornea to prevent lens decentration.
- An area of lens bearing or touch should be present in the midperiphery along the horizontal meridian approximately 3.0mm to 4.0mm from the center of the cornea at 3 o'clock and 9 o'clock to restrict lateral decentration (Figure 1).
- The lens should maintain unobstructed movement along the vertical meridian.
Figure 1. Illustration of a reverse geometry lens on a post-LASIK cornea with slight apical clearance and touch at 3 o'clock and 9 o'clock.
Figure 2. Patient EL's corneal topography. Note that the flattest spot on his cornea was 32.75D.
Because of the oblate shape of post-LASIK corneas, excessive apical clearance and fixed bubbles may occur beneath the center of a spherical diagnostic lens. In this situation consider a reverse geometry lens design in which the central radius is flatter than the midperiphery. The lens creates a plateau configuration, thereby decreasing the volume of tears beneath its center.
One example of such a plateau configuration is the Paragon CRT lens (Paragon Vision Sciences). We've found the off-label use of this design extremely versatile for post-LASIK patients interested in daily wear correction.
A case in point is patient EL who underwent bilateral LASIK surgery in April 2000. He experienced a post-operative ectasia OD and underwent a PKP in December 2001. For the past three years he has worn a GP lens OD with a visual acuity of 20/20.
Figure 3. Fluorescein pattern of EL's CRT lens on his post-LASIK left eye.
Recently, EL requested that we fit his left (post-LASIK) eye with a contact lens to resolve symptoms of halos and glare with his best-corrected spectacle correction. His simulated K readings were 35.00 @ 174/38.00 @ 84 with the flattest point on the cornea 32.75D (Figure 2).
We diagnostically fit EL with a Paragon CRT lens, 9.2mm base curve, +0.50D power, return zone of 0.500 and a landing zone angle of –34 (Figure 3). Manifest refraction over the lens was –7.50D with an endpoint VA of 20/20. Today he enjoys excellent comfort and binocular vision. CLS
Patrick Caroline is an associate professor of optometry at Pacific University. He is also a consultant to Paragon Vision Sciences and SynergEyes, Inc. Mark André is an associate professor of optometry at Pacific University. He is also a consultant for CooperVision and SynergEyes, Inc.