Fitting Contact Lenses After a Corneal Transplant
By Loretta B. Szczotka-Flynn, OD, PhD, MS, FAAO
The need for contact lenses after corneal transplantation is very common, with ~50 percent of patients requiring them for visual rehabilitation after penetrating keratoplasty (for keratoconus) (Geerards, 2006). Fitting such lenses can be challenging, and advancements in this area occur continually. So many rapid improvements to specialty lens designs have occurred in the last 10 years that it is difficult to keep the classic textbooks updated. This article is an attempt to fill in the gaps with recent peer reviewed literature regarding contact lens fitting after keratoplasty.
The most common indications for contact lens use after penetrating keratoplasty include irregular astigmatism (62.9 percent), spherical anisometropia (57.1 percent), and astigmatic anisometropia (54.3 percent) (Weitharn, 2004). Postoperative astigmatism is the main reason for unsatisfactory visual results after grafting. The number of grafts exhibiting a low amount of corneal astigmatism is rather low: <3D of astigmatism two years after transplantation ranges between 27 percent and 34 percent, depending on the indication for grafting (Gruenauer-Kloevekorn, 2005).
The average interval between penetrating keratoplasty and initial contact lens fitting usually begins at one to three months after surgery (Gruenauer-Kloevekorn, 2005; Weitharn, 2004; Geerards, 2006) although it usually averages about eight to nine months after surgery (Geerards, 2006). Sutures are often present (25 percent to 40 percent of cases) at the time of fitting (Gruenauer-Kloevekorn, 2005; Weitharn 2004). In a series of patients fit at The Department of Ophthalmology, University of Florida in Gainesville, spherical GP lenses were by far the most common lens type used and accounted for ~77 percent of eyes. These were followed by bitoric GP lenses in ~9 percent of eyes.
Traditionally, corneal topography is used to determine the global corneal shape and to select the best lens design. Whenever I teach residents, students, or even other clinicians on methods of fitting post-transplant patients, I reinforce that selecting the base curve is not the first place to start. First, you must gain an understanding of the corneal shape and then select the appropriate design; for example, reverse geometry lenses are typically fit on oblate grafts while bitoric lenses are fit only if the astigmatism is fairly regular and spans at least the central 6mm of the cornea. One group from Germany uses sophisticated Fourier analyses and determines corneal eccentricity by decomposing corneal topography maps to determine the starting design (Gruenauer-Kloevekorn, 2005). Specifically, they fit a tri-curve design when the eccentricity is between 0 and 0.4, a keratoconus design when the eccentricity is greater than 0.7, and a reverse geometry design in cases of negative eccentricity (Gruenauer-Kloevekorn, 2005) (Figure 1).
Figure 1. A post-penetrating keratoplasty cornea that has negative eccentricity and should be fit with a reverse geometry lens.
A group from the Netherlands uses corneal topography to select the initial base curve of an intralimbal lens design. They uniformly fit tetracurve contact lenses that have an overall diameter of 12.0mm and a back optic zone diameter of 8.5mm made in Boston XO (Bausch + Lomb) or FluoroPerm 151 (Paragon Vision Sciences). They select the lens back optic zone radius using tangential (rather than sagittal) videokeratography values over the elevated edges of the transplant wound (with the sutures in place) (Eggink, 2001). Specifically, the corneal radius of the most regular ring segment, displayed over at least two clock hours at the inner side of the elevated wound ridge, is used to select the initial diagnostic lens with an identical back optic zone radius. When two or more regular ring segments over two clock hours are visible on the ring map, they choose the ring segment with a corresponding radius nearest to 7.70mm, the radius of a normal eye.
If sutures are present, it is fairly common to expect at least one broken suture during the post-fitting follow up. For example, in one study 35.7 percent of eyes that had intact sutures at the time of initial lens fitting experienced a broken suture at some point after lens fitting (Weitharn, 2004).
Specific Lens Types
Specific lens types reported in the literature as successful after keratoplasty are not necessarily reflective of what is being used in practice. Rather, some larger (typically academic) practices review their data on a series of patients that they have fit with a specific lens type and submit it for publication. There are several such publications that discuss the use and success of scleral lenses, a proprietary intralimbal lens, a specific hybrid lens, and the Menicon Z (Menicon) material.
Ozbek and Cohen (2006) at the Cornea Service of Wills Eye Hospital reported on 27 eyes fit with the Dyna IntraLimbal Lens (Lens Dynamics); six of these eyes were fit after penetrating keratoplasty. This lens is a large-diameter (typically 11.2mm or 10.8mm) GP with a proprietary design often manufactured in Menicon Z but can also be ordered in other GP materials. The authors typically used Fluoroperm 60 (Paragon) in their case series, which included keratoconus, pellucid marginal degeneration, and post-keratoplasty patients that had flat central corneas with steeper inferior peripheries. The initial base curve selection suggested by the manufacturer is equal to the radius of the cornea 4.0mm from the center on the temporal side of the topographic map. The authors chose the initial Dyna IntraLimbal base curve according to the central topographically derived flat value and modified later depending on the position and movement of the lens and patient comfort. About 67 percent of all patients were still successfully wearing the lens at the last follow-up visit, which averaged about nine months.
Visser et al (2007) published a case series of 284 eyes fit with scleral lenses, of which ~20 percent were fit after keratoplasty. They fit almost an equal amount of spherical lenses and back-surface toric lenses, but ultimately achieved 100 percent success, with all patients being able to remain in a scleral lens throughout a five-month follow-up period.
Nau et al (2008) published a case series of 79 eyes fit with the SynergEyes lens (SynergEyes) at the Contact Lens and Low Vision Services at the UPMC Eye Center, University of Pittsburgh; 15 percent were fit after penetrating keratoplasty. After three months, 52 percent of patients overall reported no problems, and about 80 percent reported that their comfort was improved compared with traditional rigid lens designs.
Patel and I (2008) published a case series of 40 patients who had irregular corneas fit with the Menicon Z material; 20 of the patients were fit after keratoplasty. Overall there was a 74-percent success rate with this material in a group of patients after corneal surgery and in other non-keratoconic irregularity, and only one eye (3 percent) failed directly due to inability of the material to perform adequately; another material was ultimately acceptable.
These are good sources in the literature to review, as I believe that they do indeed mirror the trend in lens fitting after penetrating keratoplasty compared to a decade ago. That is, such fitting has largely shifted to larger-diameter lenses—including those that sit on the sclera—in highly oxygen permeable materials. CLS
For references, please visit www.clspectrum.com/references.asp and click on document #190.
Dr. Szczotka-Flynn is an associate professor at the Case Western Reserve University Dept. of Ophthalmology & Visual Sciences and is director of the Contact Lens Service at University Hospitals Case Medical Center. She has received research funding from Ciba, Vistakon, Alcon, and CooperVision. You can reach her at loretta.szczotka@UHhospitals.org.