GP Lens Options for Post-Graft Patients
BY NANCY CHAN, OD, & JOHN MARK JACKSON, OD, MS, FAAO
Undergoing a penetrating keratoplasty (PKP) can be a life-altering experience. PKP will solve many patients’ corneal problems and will enhance their quality of life; for others, the visual outcome is less than ideal. We will review the indications for PKP and what GP lens options are available for providing optimal vision correction in these patients.
Indications for PKP
A patient may need a PKP for many reasons, including keratoconus, corneal dystrophy, corneal scarring, and bullous keratopathy, among others (Kanski et al, 2011). Although many patients have good vision with glasses following the procedure, many are left with irregular astigmatism and anisometropia (Wietharn and Driebe, 2004), which, of course, can cause aniseikonia when the difference between eyes is too great.
Typically, in cases of anisometropia, contact lenses will equalize the retinal image sizes better compared to glasses.
Fitting GP Lenses Post-PKP
GP lenses are a great choice post-PKP for several reasons: GP lenses provide superior optical performance, particularly in cases of irregular and high-normal astigmatism; they have high oxygen permeability; and they have a lower incidence of microbial keratitis and neovascularization compared to soft lenses (Cheng et al, 1999). Of course, corneal GPs require an initial adaptation period that can impact comfort.
Corneal topography is a necessity when fitting a post-PKP patient. The normal shape is prolate (flattening from center to periphery) (Figure 1), but an oblate cornea steepens from center to periphery (Figure 2) and is often the result of a “sunken” graft. A prolate shape can be fit with a standard GP, while an oblate shape will usually need a reverse geometry design (Szczotka and Lindsay, 2003). Due to the often irregular topography, a special quadrant-specific lens design may also be indicated (different base curves or peripheral curves in each quadrant).
Figure 1. Highly prolate post-PKP cornea.
Figure 2. Highly oblate post-PKP cornea.
If you can’t achieve adequate centration or alignment of the irregular cornea, consider a hybrid or scleral lens (Ozkurt et al, 2012). Hybrid lenses, such as the SynergEyes PS or UltraHealth (both SynergEyes), have a rigid center surrounded by a soft “skirt.” These lenses provide GP optics with comfort that is similar to a soft lens. Scleral lenses vault the cornea and rest on the scleral conjunctiva, making them very stable. The constant tear reservoir between the lens and cornea masks corneal irregularities and astigmatism while protecting the cornea from desiccation and from lens friction with blinking (Severinsky and Millodot, 2010). CLS
For references, please visit www.clspectrum.com/references and click on document #223.
Contact Lens Spectrum, Volume: 29 , Issue: June 2014, page(s): 17