A Post-Hyperopic LASIK Fitting
BY ANN LAURENZI, OD, FAAO
A 48-year-old patient was referred to the contact lens department after hyperopic LASIK surgery in each eye in November 2004 and LASIK enhancement surgery in each eye in April 2005.
After the LASIK enhancements, the patient was told she needed cataract removal and had an intraocular lens placed in the left eye in November 2005. She also had a history of amblyopia OS and underwent muscle surgery at age 5 for strabismus in the left eye. She had persistent postsurgical blurry vision with distortion. The patient did not want any further surgery and opted for contact lenses to improve her vision.
Visual acuity without correction was 20/40 OD and 20/70 OS, correcting to 20/25 OD and 20/50 OS. Manifest refraction was OD +0.50 –1.25 × 156; OS +0.25 –1.00 × 114. Topography revealed a central steep zone approximately 5.5mm in each eye.
The hinge of the LASIK flap was nasal in both eyes, which created a flatter localized area in that portion outside the lasered treatment zone. The postsurgical topographical pattern is representative of a typical hyperopic LASIK treatment with a 6.0mm optic zone ablation and a transition zone out to 8.5mm. Remember, myopic ablations tend to create oblate post-surgical topographical patterns while hyperopic ablations steepen the central zone.
Sim Ks OS were 50.62D and 49.75D and flattened to 39.3D at 2.46mm inferior nasal from center (Figure 1). The optic zone was free of severe irregularity, but the wavefront showed significant negative spherical aberration. The Sim Ks OD were 49.37/45.62 but dramatically flattened outside the central 3mm zone (Figure 2).
Figure 1. Patient's corneal topography OS.
Figure 2. Patient's corneal topography OD.
Choosing a Lens
Design options were limited by the topography, visual acuity (VA) and the patient. The former GP wearer had requested GPs as she had handling issues with soft lenses. We also discounted hybrids or piggybacks for this reason even after ample application and removal training. VA and quality were also better with GPs than with soft lenses.
Larger-diameter lens designs with base curves steep enough to align with the central cornea caused bearing on the much flatter peripheral, non-treated cornea, creating seal-off and debris entrapment. We designed GPs with a small overall diameter (7.5mm) and central alignment fit with a low edge clearance. The optical zone covered the steep ablation zone while four peripheral curves contoured the early corneal transition zone of the treatment area without encroaching on the non-treated portion of the cornea. A lower edge clearance allowed lids to smoothly blink over the lens without dislodging it and allowed adequate tear flow under the lens.
The final parameters were OD 7.07mm base curve; 7.5mm OAD, 6.60mm optical zone, pentacurve design and OS 7.60mm BC, 7.6mm OAD, 6.60mm OZ, pentacurve design. The patient comfortably wears her contact lenses up to 10 hours a day and achieves a VA of 20/20 OD and 20/30 OS. CLS
Dr. Laurenzi practices at the Cole Eye Institute in Cleveland, Ohio where she specializes in refractive surgery co-management, contact lenses and clinical research.