contact lens case reports
A Custom Soft Lens for Post-RK Hyperopic Shift
BY PATRICK J. CAROLINE, FAAO, & MARK P. ANDRÉ, FAAO
Radial keratotomy (RK) cut its way through the eyecare industry in the 1980s. An unforeseen complication of the procedure was first described by Deitz and Sanders in 1985, a phenomenon they referred to as progressive hyperopia. Also known as hyperopic shift, progressive hyperopia is an ongoing effect of the surgery in which there is continued corneal flattening and a continued decrease in the minus power. Deitz and Sanders reported that 31 percent of 225 eyes showed a hyperopic shift of 1.00D or more between one-to-three years following surgery. All subsequent studies have confirmed this finding.
Perhaps the best data we have are the 10-year results of the Prospective Evaluation of Radial Keratotomy (PERK) Study in which 43 percent of patients showed a 1.00D or greater hyperopic shift. The exact mechanisms responsible for this continued effect remain unknown.
A Significant Case
Our patient was a 52-year-old female who underwent bilateral RK in 1989. Her right eye has remained stable, but her left eye experienced a significant hyperopic shift. Her uncorrected visual acuities were OD 20/20 and OS 20/400. Her manifest refraction was OD +0.50 −0.50 x 55, 20/20 and OS+5.75 −1.00 x 75, 20/25. Keratometric readings were OD 39.75 @ 7/40.37 @ 97 and OS 35.75 @ 80/37.00 @ 170 (Figure 1). Slit lamp examination showed more than 24 radial incisions in both eyes and the presence of a central “iron star” in the left eye only (Figure 2).
Figure 1. Patient's corneal topography, note the differences between the right and left eyes.
Figure 2. Slit lamp view of the patient's left eye without (left image) and with (right image) the soft lens.
Because of the high degree of anisometropia, we elected to fit a custom soft lens manufactured by Medlens Innovations. The design incorporates two radii on the posterior lens surface, a flat central radius to align the flat central cornea, and a steeper (normal) radius to align the more normal midperipheral and peripheral cornea. Ultimately, we dispensed a lens with base curve radii of 9.70mm and 8.60mm, powers of +6.50 −1.00 x 075, and a diameter of 14.8mm in a 59-percent-water HEMA material. The patient achieved a visual acuity of 20/25 with comfortable all-day wear.
Figure 3. Parallelepiped view of the soft lens across the central cornea.
We will monitor her for the inevitable incisional neovascularization with the hope that we will soon have additional FDA-approved lathable silicone hydrogel materials for custom designs. CLS
For references, please visit www.clspectrum.com/references.asp and click on document #166.
Patrick Caroline is an associate professor of optometry at Pacific University. He is also a consultant to Paragon Vision Sciences. Mark André is an associate professor of optometry at Pacific University. He is also a consultant for CooperVision.