BY EDWARD S. BENNETT, OD, MSED
GP Lenses and the Global Keratoconus Congress
The recent Global Keratoconus Congress (GKC) was a two-and-one-half day symposium which presented the most up-to-date research and clinical management techniques for keratoconus. Although the October GP issue will further highlight the findings of this meeting, I’ll discuss some GP application results here.
GP Lens Designs with Variable Peripheral Eccentricities. Several presenters discussed the performance and applications of posterior surface geometries that varied in peripheral eccentricity in every quadrant. For example, in the case of excessive inferior edge lift you can design a lens that has a 0 eccentricity inferiorly, 0.3 eccentricity in the nasal quadrant (if the apex is displaced in this quadrant), 0.6 temporally and >1.0 superiorly. The future is exciting with manufacturing technology being such that these — and even more sophisticated designs — will become increasingly available in the next few years. This should result in more comfortable fitting relationships, longer wearing time and possibly a reduction in lens-induced corneal staining.
Large- vs. Small-Diameter Lenses. There’s been an increasing number of large-diameter (often 10mm to 12mm) GP lenses for post-surgical and keratoconus applications. Large-diameter lenses are most successful with an inferior decentered apex as well as with large or globus cones.
GP Lenses and Corneal Scarring. Karla Zadnik, OD, PhD, reported that the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) study found that 38 percent of keratoconic patients who had a corneal curvature greater than 52.00D had corneal scarring. In addition, each diopter they were fit flat with GP lenses increased the risk of corneal scarring by 19 percent.
Bitoric Lens Applications in Keratoconus. Due to the irregular nature of keratoconic corneas, bitoric lenses are often contraindicated. However Sigrid Neumann, Dipl.Ing. (FH) der Augenoptik, of Germany discussed how, over a four-year period, she fit almost 60 percent of her keratoconus patients into bitorics. Her case reports emphasized the importance of assessing each patient’s corneal topography and fitting bitoric lenses if the astigmatism is fairly symmetrical.
Piggyback Lens Systems Michael Ward, MMSc, FAAO, reported on the use of piggyback lens systems, notably in cases of GP lens failure, apical nodules, keratoconus-like post-surgical ectasias or used simply as a temporary crutch. He described two piggyback fitting methods: fit the GP lens to the cornea and then place the soft lens under this GP, or fit the soft lens first and perform over-keratometry, then select a GP lens with a base curve equal to the flat over-keratometry value. He also suggested using a hyper-Dk GP lens material with a silicone hydrogel soft lens material. He recommended using Menicon ESC (Menicon) for cleaning the GP lens and Complete (Advanced Medical Optics) for wetting and storage of both lenses.
Hybrid Applications for Keratoconus Dianne Anderson, OD, reported on a series of keratoconus patients successfully fit into the SynergEyes A and SynergEyes KC (SynergEyes, Inc.) lens designs. She found sufficient apical clearance in lenses fit, on average, 1.34D steeper than average Sim K. She defined optimum clearance as the absence of both central bubbles and bearing.
More to Come
Other important findings from the GKC will appear in much detail in October. One of the most remarkable aspects of this meeting was the knowledge and expertise of the attendees. It’s evident that we’re all looking for more ways to manage challenging irregular cornea patients. CLS
|Dr. Bennett is an associate professor of optometry at the University of Missouri-St. Louis and is executive director of the GP Lens Institute.|