contact lens case reports
Corneal Sphericalization After Penetrating Keratoplasty
BY PATRICK J. CAROLINE, FAAO, & MARK P. ANDRÉ, FAAO
Since the first modern corneal transplant in 1952, surgical outcomes have steadily improved secondary to evolutions in surgical techniques, advances in topical anti-inflammatories and refinements in corneal preservation techniques. Complications such as graft rejection and glaucoma have decreased, leaving anisometropia or high regular and irregular astigmatism as the most common post-operative complications. In most cases these refractive complications require some form of contact lens correction to achieve maximum visual acuity and binocularity.
Fitting Post-Graft Corneas
The topographical, optical and physiologic demands of the graft represent a major challenge. With the advent of today's high-Dk GP lens materials and advanced computer-controlled lathing systems, it's now possible to design and manufacture almost any functional lens shape.
Figure 1. The patient's post-PK topography and K-Max lens OD.
One such advanced lens design is the K-Max (Valley Contax), which incorporates a spherical posterior center and an aspheric midperiphery and periphery. This 12.0mm-overall-diameter lens has a wide range of applications for highly irregular or asymmetric corneas.
Our patient was a 38-year-old male who underwent corneal transplant surgery to the right eye in November 2005 for uncorrectable post-LASIK ectasia. One year post-op his simulated keratometric readings stabilized at 35.87 @ 32/50.50 @ 122 with 14.75D of corneal astigmatism. We attempted a number of toric lens designs, but the lenses failed to provide adequate comfort and visual acuity. We eventually fit the patient in the K-Max design, which ultimately provided excellent comfort, wearing time and 20/15 visual acuity (Figure 1).
The story doesn't end there. On the patient's last follow-up visit, we noted that his flat corneal meridian had steepened along the 30 degree meridian by approximately 5.00D (Figure 2). This corneal sphericalization is a common finding in post-PK patients who have been fit with GP lenses. Whether the sphericalization is secondary to ongoing wound healing at the graft/host interface or perhaps to a molding of the cornea to the posterior lens surface is unknown at this time. It's been our clinical experience that corneal sphericalization does exist and that rigid lenses do indeed have a positive effect in influencing the shape of these more moldable corneas. CLS
Figure 2. Difference display map showing corneal sphericalization.
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 and SynergEyes, Inc.