Sponsored by IOT
By Deborah Kotob, ABOM
The sensation is an uncomfortable, unnatural feeling of unsteadiness for anyone who has experienced the “swim effect” when wearing and trying to adapt to progressive lenses. The wearer experiences a non-stable perception of surroundings. The swim effect causes discomfort and reduces overall lens satisfaction, making adaptation more difficult. Despite advancements in progressive lenses, some patients still experience this effect.
“Until Steady Methodology, reducing the distortions and image instability experienced by the wearer during off-axis gaze generally addressed the unwanted cylinder component of the spherocylindrical error inherent to progressive lenses. But lateral distortions in progressive lenses are spherocylindrical in nature, meaning there are spherical power errors and unwanted cylinder errors inherent in the areas adjacent to the progressive lens corridor (umbilic). Since both the cylindrical and the spherical (mean power) errors contribute to distortion and the resultant swim effect, it follows that both should be minimized to their geometrical limits.
Steady Methodology – Inspired by Stability IOT optical engineers have empirical optometric evidence that controlling the placement and amount of mean power and cylinder errors lateral to the progressive lens corridor could dramatically reduce the swim effect and peripheral aberrations. Correcting mean power error is a breakthrough progressive lens design. Mean power error is a problem in peripheral lens optics that significantly affects the amount of blur and swim effect experienced by the patient. In the past, lens designers concentrated on minimizing and precisely placing unwanted astigmatism to reduce lens distortion, but uncorrected mean power error contributes significantly to blur and swim effect.
IOT’s Steady Methodology new design tools combined with advanced mathematics control the power distribution for sphere and cylinder power error. Near null power error is achieved in the lateral areas of the progressive lens, and the patient experiences immediate improvement in overall visual performance. Image stability is achieved by minimizing distortion in the periphery of the lens. Steady Methodology is an IOT patented technology supported by empirical optometric evidence resulting from years of investigative research and clinical trials.
Typically, lateral areas of a progressive lens have a positive mean power error value that our eyes’ accommodative system cannot negate. However, Steady Methodology technology lenses exhibit mean power error values near 0, decreasing distortion levels and improving visual acuity. How is this achieved? “In an internal study carried out by IOT, the limits of tolerable defocus that maintain stable visual acuity in presbyopes were evaluated. Monocular visual acuity was measured at a distance of 5.5 m by the ETDRS charts (PVVAT Software, Precision Vision, La Salle, III) with the interposition of different combinations of spherical and cylindrical lens powers, having a spherical equivalent (mean power) ranging from -2.00D to +1.00D. The results indicate that there is a range between +0.25D and -0.75D in which users with accommodation amplitude lower than 1D maintained stable visual acuity.” (MORE EFFICIENT VISION THROUGH SUPERIOR IMAGE STABILITY; Eva Chamorro, Ph.D., José Alonso, Ph.D., and Dr. Daniel Crespo, Ph.D.)
IOT’s patented Steady Methodology and Steady Plus Methodology are technological breakthroughs in free-form, digital lens design. In addition to controlling for unwanted cylinder power, the Steady Methodology strictly controls mean power, virtually eliminating spherical/mean power errors in the lateral areas of the lens for superior image stability and visual comfort, all while achieving a significant reduction of unwanted astigmatism. For the wearer, this means better lateral vision with superior image stability. Steady Methodology is now incorporated into every general use IOT progressive design. Now, all IOT progressive lenses provide the superior optics of this technology for each lifestyle and market segment. In addition, Camber’s progressive lenses also include the Steady Plus Methodology, an improvement to Steady Methodology that provides superior binocular visual performance for mid-range and near vision. Furthermore, the reduction of the swim effect when wearing progressive lenses and the increased useable lens area for more expansive undistorted fields of view ensures more satisfied progressive lens wearers.