Soft Lenses for Keratoconus

By Barry Farkas, O.D.
DEC. 1996

Not all keratoconus patients can easily tolerate wearing properly prescribed rigid contact lenses. This is especially true since these lenses require very steep base curves to vault over the cornea, resulting in high minus lenses with thicker peripheries.

Some of these patients, generally the same individuals who can be well corrected with spectacles, can achieve contact lens success with hydrogel lenses. Compared to spectacle corrections, hydrogel lenses decrease the induced distortion, as well as eliminate the unattractive appearance of highly astigmatic prescriptions.

THESE KERATOCONUS PATIENTS ACHEIVED GOOD VISION AND IMPROVED COMFORT WITH HYDROGELS.

IDENTIFYING HYDROGEL CANDIDATES

How can we screen keratoconus patients to identify acceptable hydrogel lens wearers? Refractive results are an important indicator, but so is baseline corneal topography.

Topography is a quick and easy procedure in most offices, since it's usually delegated to a technician. When evaluated with best corrected refractive prognosis, topography can yield a reasonably valid prognosis.

Look for low positioned cones with mostly regular topography within the pupillary areas. One eye will invariably display greater regularity than the other, but as long as the irregularity is minor in the central portion, you can expect reasonably good visual correction and binocular function.

DETERMINING THE APPROPRIATE PRESCRIPTION

Next, trial fit hydrogel toric lenses that approximate the derived spectacle prescription. Calculate the prescription through a spherocylinder overrefraction and order the resultant initial lenses. You may have to repeat the spherocylinder overrefraction several times to achieve an optimal result. Don't be surprised if the final lenses vary considerably from the spectacle prescription, since the contact lenses are being twisted and stretched by an extremely irregular cornea, as well as by the normal forces of nature.

The above maps are corneal topographical findings for two recently fitted keratoconus patients. Both patients were able to tolerate optimally fitted modified apical clearance rigid lenses (feather touch), but they reported each day's experience as more pain than pleasure. Both are achieving reasonably good hydrogel visual correction (not as precise as with RGPs, but good enough) at 20/20^-1 in the less progressed eye and 20/25^-2 in the more advanced eye. Most importantly, both are thrilled with the result!

Hydrogel lenses will never replace judiciously designed RGPs for the majority of keratoconus patients. For the fortunate few, however, they are pieces of plastic from heaven. Our office sees literally hundreds of keratoconus patients on a regular basis and those patients with the bigger smiles are the ones wearing hydrogels. So, plug in that topographer and try hydrogel lenses for this most needful segment of your patient population. CLS

Dr. Farkas, who specializes in contact lenses, is a diplomate and former chair of the Cornea and Contact Lens Section of the American Academy of Optometry. He is in group practice in New York, N.Y.