Tech Connection
The Challenge of HOA-Correcting Contact Lenses
In pursuit of "perfect" vision.
By Louis J. Catania, O.D., F.A.A.O.

IF SPECTACLES THAT CORRECT higher order aberrations (HOAs) turn you on, think about HOA-correcting contact lenses! They will change the face of vision correction and create a "feeding frenzy" among contact lens marketers. Thus, it's critical for clinicians to know the challenges and limitations of HOA-correcting contact lenses as well as their potential.

Off-the-rack vs. Tailor-made

HOA-correcting contact lenses will fall into two main categories:

1.    Generic aspheric lenses. These lenses, which are already being marketed, will benefit patients who have a lot of positive spherical aberrations.

2.    Individually designed lenses. These lenses will have programmed central optics, requiring pupil registration for point-to-point Zernike correction.

An aspheric correction is like a suit off the rack. It may not be a bad fit and usually looks pretty good. But a point-to-point correction is a custom-made suit that looks and fits "perfectly."

This tailored-fit analogy raises an interesting business consideration for eyecare practitioners in this evolving field of HOA-correcting contact (and even spectacle) lenses. When you measure and fit a true, point-to-point correcting lens, you hold a unique, personalized prescription for that patient. Once a person adjusts to and enjoys HOA correction, "off-the-rack" lenses will no longer suffice. This is no small consideration in this era of drug-store and mail-order contact lenses and eyeglasses.

Achieving this personalized correction has some formidable challenges well beyond those of the generic, aspheric form of correction. However, meeting these challenges has the potential of producing the optimal vision-correcting modality.

Seeking Stability

The main challenges associated with point-to-point pupil correction with a contact lens relate to stabilizing fit. The movement (like lag), decentration, flexure and the like must be controlled. Otherwise, these factors will negate precise alignment or registration between correcting points and pupil powers.

The trick, of course, is to fit the lens tight enough to eliminate these factors, while maintaining corneal physiological and morphological integrity. One way to accomplish the former (tightness) is obvious: Make the lens larger and steeper. We've been doing that since the good old days of scleral haptic shells.

But tightness breeds hypoxia in con-
tact lens wear. Current and future high-Dk materials will need to address the challenge of balancing perfect lens stability with uncompromised corneal health. Other creative ways of stabilizing lenses — bioadhesive materials, implantable lenses (onlays) anchored by the epithelium and collagen lenses — are under investigation.

Another Variable: Tear Film

HOA-correcting contact lenses have the potential to provide vision that's superior to that achieved from any other form of correction, either nonsurgical or surgical. The key to achieving this potential lies in the lens surface. Point-to-point HOA correction combined with control of the variable tear film — the true refracting surface of the eye — is the real likelihood of producing "piston" in human vision. And, if you think about it, a contact lens is the only device that can accomplish both.

So there's our future!