Sponsored by IOT
By Laurie Pierce, ABOM
There is no end to the complexities associated with correcting vision. Laurie Pierce recently spoke with Dr. Peter Shaw, who invented the Shaw lens, to address several of those complexities. Aniseikonia is an ocular disorder characterized by dissimilar ocular images received in the brain, and anisophoria is due to the difference in prismatic effect associated with unequal refractive powers in eyeglasses. Pierce shares what she learned from her interview with Dr. Shaw.
I had the distinct honor to speak with Dr. Peter Shaw, who invented the Shaw lens. Shaw’s interest in optometry began at age 15, when he was diagnosed with a strong refractive error which impaired his ability to see at a distance. His love of physics, mathematics, chemistry and computer science were the perfect ingredients for what he calls his “passion for human engineering.” He applied that passion to develop the Shaw lens.
The Shaw lens is an innovative solution for the correction of aniseikonia.
Although each eye, individually, can see 20/20, the different magnification sizes focused on the retinas when fused cause visual disruption in the brain. What makes the Shaw lens unique is its use of complex mathematics to balance the retinal image sizes in different positions of gaze.
“When we think about correction for anisometropia and antimetropia, we think of slab off prism, or reverse slab,” Shaw explains. “While that corrects for vertical imbalance at near, while reading, it does not correct the imbalance when looking through different parts of the lenses.”
Shaw’s consideration of other positions of gaze (looking up and looking side to side for example) was a game changer. “If the right eye sees a big image, and the left eye sees a small image, the right eye will have to turn farther up to see the top of the image. This is a problem,” he says. “The lenses create a prismatic effect between the two lines of sight.”
The prism causes double vision, so when the patient looks up there is a disparity. The patient starts to see double. And when the patient looks down through the reading area of a bifocal or progressive lens, the words seem to split apart. It’s called “dynamic aniseikonia” because it involves the eyes moving in the world to look at things.
Shaw lens works in concert with the power of the IOT free-form design engine by optimizing thickness, curvature and surface geometry to reduce or eliminate aniseikonia.
Shaw compares aniseikonia to stereo speakers. “When you listen to the stereo, and the right channel is delayed a little bit from the left channel, you get what sounds like an echo. Similarly, with aniseikonia, when looking at a picture, the images created are different, sort of like a visual echo. The brain has difficulty fusing the two images as one.”
The Shaw lens applies Snell’s Law formula and aspheric surface 3D ray tracing to address aniseikonia, anisophoria, barrel distortion and swim. Building on our early understanding of manipulating base curves, thickness and index of refraction, the Shaw lens incorporates complex algorithms via free-form technologies developed by IOT. It corrects for optics and improves aesthetics by avoiding drastically different base curves between the right and left lenses.
“These calculations go beyond Prentice’s Rule, which puts us in the ballpark, but does not provide other slight power and design changes necessary for correcting these visual imbalances at all positions of gaze,” Shaw says.
Who is the best candidate for the Shaw lens? Certainly, those with aniseikonia, but anisometropes and antimetropes are also great candidates. The Shaw lens considers correcting the optics when looking up and out the sides, not just while looking down to read.
Listen to your patients, Shaw recommends.
“Our patients do not have the technical terms to explain their visual complaint to us. Instead, they may say, “I see double headlights when looking to the left, but not to the right,” or “When I am wearing my eyeglasses, my vision just feels uncomfortable.” It is our job to employ active listening skills to unravel what is really going on and direct patients to an excellent optical solution, such as the Shaw lens!
