Managing Compromise With Large-Diameter Corneal GPs
By Gregory W. DeNaeyer, OD, FAAO
The trend toward manufacturing and fitting large-diameter corneal GP lenses has improved success in managing patients who have irregular corneas. Large-diameter GPs have diameters between 10mm and 12mm. Their larger size allows for more even bearing distribution on corneas that have atypical topography.
However, because corneal GPs have limited vaulting capabilities, you may find that areas of uneven bearing manifest when fitting severely irregular corneas. In such cases, scleral lenses would be a better option; unfortunately some of these patients may not be candidates for scleral lenses secondary to issues such as small apertures or physical disabilities.
With that in mind, what defines success of a large-diameter corneal GP on an irregular cornea if you are unable to achieve the ideal near-alignment fit?
Increased lens-to-cornea interaction at areas of bearing does not always impact epithelial integrity in a negative way. Minimize areas of bearing as much as possible, then monitor the cornea carefully at follow-up exams after dispensing the lens. Be sure to remove the lens and add fluorescein to check for areas of staining.
Address areas of epitheliopathy by either creating more vault or cushioning the impact of the GP lens by piggybacking it on a soft lens. You don't necessarily have to refit the GP lens in this case—simply piggyback the lens you already have and evaluate. Using a lens design that incorporates quadrant-specific adjustments may also improve the fit.
A patient has to obtain significant comfort with a lens or the case will fail. Generally, large-diameter corneal GP lenses are more comfortable compared to their relatively smaller (8.5mm to 9.5mm) GP counterparts because of broader weight distribution and less movement with blinking.
Patient comfort usually coincides with corneal health, so many patients can adapt even if there is a significant bearing spot as long as the epithelium is not compromised. This occurs frequently in keratoconus patients. As stated previously, increasing vault, piggybacking, or utilizing quadrant-specific technology may address surface staining and secondary comfort issues.
Excessively high-riding lenses may be uncomfortable secondary to conjunctival injury from the lens edge. Steepening the lens often helps to lower it into a centered position. Isolated areas of edge lift or corneal impingement can be corrected by using a quadrant-specific lens design.
Ultimately, you want to maximize optics for irregular cornea patients as much as possible. Patients may benefit from a lens design that has aspheric front-surface optics to minimize spherical aberrations. Acuity may be diminished and/or variable if there is too much central pooling, so try for near alignment when possible. Jinabhai et al (2010) reported that fitting GP lenses flatter on keratoconic eyes reduced higher-order aberrations and improved acuity.
A successfully fit large-diameter corneal GP lens on an irregular cornea doesn't compromise corneal health, is comfortable to wear, and provides the patient with their best potential vision. The lens fit may not look text-book, but it doesn't have to if these criteria are met. CLS
For references, please visit www.clspectrum.com/references.asp and click on document #182.
Dr. DeNaeyer is the clinical director for Arena Eye Surgeons in Columbus, Ohio. His primary interests include specialty contact lenses. He is a consultant or advisor to Visionary Optics and an advisory panel member of Inspire Pharmaceuticals. Contact him at email@example.com.