FOCUS ON LOW VISION

Digital Surfacing In Low Vision?

Here’s why wavefront-controlling lenses might work for some low vision patients

there are no peer-reviewed studies I’ve seen, but I nonetheless think there is merit in considering digitally surfaced, wavefront-controlling lenses for some low vision patients. This is an approach most low vision practitioners may not have considered.

As an optician who specializes in low vision and has a pretty good understanding of the benefits of these newer designs, it makes sense to me.

SURFACE ACCURACY

A digital surfacing lab can produce a plain old spherical lens as easily as the most exotic wavefront correcting designs, so just calling it digital doesn’t make it great. What digital surfacing does provide, however, is the ability to produce a surface with such accuracy that we can begin to control distortions that have only been partially addressed with best-corrected curve designs.

There are a number of companies that do a good job of controlling the wavefront through the spectacle lens. For folks with healthy eyes and correctable vision, these designs make vision sharper and can create a “wow” factor. Could low vision patients have a similar experience?

As one low vision practitioner told me: “The better the acuity, the more important these specialty lenses are for the patient. My gut feeling would be if the patient is 20/80 or better, every improvement we can make is critical to get them to the 20/50 (1M) letter-size goal.” It’s like a hearing-impaired person discerning the difference between the sound of a vinyl album vs. a CD (see sidebar, page 63).

THE BENEFITS

• HIGH ADD. Wavefront-correcting lenses are available in single vision and progressive addition forms. Some PALs are available in a +4.00 add, which definitely has a place in low vision.

• ABERRATION & DISTORTION REDUCTION. The reduction of higher-order aberrations in the progression and surrounding area is significant. Single vision lenses that address the influence of higher-order problems on the overall focus on the retina may also be significant (see sidebar on left).

Wavefront-controlled designs can significantly reduce off-visual-axis lens distortions. Many low vision patients depend heavily upon peripheral vision for general orientation. They may also have devices such as telescopes mounted in their lenses that eliminate or at least encroach in the center of the lens, leaving only the periphery of the lens with its power error, distortion, marginal astigmatism, etc., to carry the load. Sharpening the vision in the periphery in a significant way is one of the benefits for a normally sighted person. Could it make a difference to some of our low vision patients?

• POSITION OF WEAR. These new lenses are taking into account position-of-wear factors to compensate for error that occurs. In some designs, factors such as eye rotation center position and natural head position are also measured, both of which could be valuable to the low vision practitioner.

As someone with considerable experience in fitting and adjusting telescopic aids, I know I would benefit from knowing the precise center of rotation. And, I have certainly observed different head positions among patients striving to find that “best spot.”

Granted, there are uncontrollable factors in the eye itself that the best digitally surfaced lenses will not correct. But if these newer designs have potential to sharpen the image formed on the retina with better focus, decrease distortion in unfavorable light conditions, and keep tight rein on factors that lens position can influence, then can we ignore the possibility that we might be able to use these lenses with some success in low vision?

— Alex Yoho, ABOM

To share your comments on the use of these designs in low vision, email the author via ayoho@cox.net