Article

THE SCLERAL LENS VAULT

FITTING KERATOCONUS

The Scleral Lenses in Current Ophthalmic Practice: an Evaluation (SCOPE) study reported that scleral lenses are primarily used to manage corneal irregularity (Nau et al, 2016). Within this category, 97.3% of respondents used scleral lenses to manage keratoconus. Although basic scleral lens fitting characteristics are the same for keratoconus, fitting strategies can differ from other irregular cornea types depending on specifics of the case.

Patient Education

Take the time to educate your patients as to why scleral lenses may benefit them. This is especially important if they have had failed attempts with corneal GP contact lenses. You can be brief with your explanation because they will experience the benefits of improved comfort and stability after application of a scleral diagnostic lens.

Lens Selection

The first consideration is choosing the scleral lens diameter. For keratoconus, the two most important factors that determine lens diameter are the patients’ corneal diameter and the severity of their keratoconus.

Start with mini-scleral lenses (15.5mm to 17.5mm) for patients who have average corneal diameters (11.7mm horizontal visible iris diameter) (Rüfer et al, 2005) or mild-to-moderate ectasia. Choose full scleral lenses (18mm or larger) for patients who have larger corneal diameters or severe ectasia.

The next consideration is contact lens geometry. Corneo-scleral topography measurements allow you to measure and design lenses that best fit each eye.

Although a prolate lens design will match nicely with the contours of a keratoconic eye, there are many cases in which a reverse geometry design will help to more evenly vault the corneal surface by creating midperipheral lift while keeping the base curve of the lens relatively flat, which can reduce aberrations and lens power.

Keratoglobus patients often require full scleral lenses with increased optic zones and significant reverse geometry for the lens to vault the cornea from limbus to limbus. Many keratoconus patients will benefit from improved-fitting lenses if customized back-surface torics or quadrant-specific haptics are designed that better align to non-spherical scleral contours.

Optical Correction

The liquid reservoir of a scleral lens masks regular astigmatism from the corneal front surface, but many patients will have residual astigmatism. It is necessary to do a sphero-cylindrical over-refraction on each fit lens to determine whether front-surface toricity will improve a patient’s visual acuity.

Multifocal optics are an option for presbyopes, but are best utilized with patients who have clear corneas and near-perfect acuity with the best-fit scleral lens. Additionally, residual higher-order aberrations can make success with multifocal optics challenging.

Corneal Cross-Linking

Corneal cross-linking has become an important step in our management of keratoconus. Any patients who have demonstrated progression, or who are at risk for progression (especially younger patients), should be evaluated for possible cross-linking treatment.

Patients can generally be fit with scleral contact lenses four to six weeks post-cross-linking treatment. However, this should be approved by and coordinated with their corneal specialist. There is evidence to suggest that cross-linking could change the shape of the sclera (Wang et al, 2012), ultimately affecting lens design.

Conclusion

While other options do exist, scleral lenses are often the best contact lens choice for your keratoconus patients. In addition, fitting your patients with scleral lenses can sometimes delay or prevent a corneal transplant. CLS

For references, please visit www.clspectrum.com/references and click on document #266.