Sponsored by IOT
By Deborah Kotob, ABOM
With the introduction of Digital Ray-Path® Technology in 2008, IOT’s pioneering research and development contributed enormously to free-form science with significant improvements in the mathematical algorithms and the optical, physiological and clinical principles used in the customization of ophthalmic lenses. Part 10 of the IOT Free-Form Insights series introduces the IOT Endless® personalized single vision lens design, powered by IOT’s new Digital Ray-Path® 2 digital design technology.
DIGITAL RAY-PATH 2 COMPENSATING OBLIQUE ABERRATIONS
To fully appreciate the technological leap behind the IOT Endless personalized single vision lens design, we must understand how its backbone Digital Ray-Path 2 Technology works synergistically with the crystalline lens’ natural ability to accommodate small negative oblique spherical aberrations. We must also understand how Digital Ray-Path 2 accounts for object space in the compensation of oblique aberrations in single vision lenses. If we learned anything from Parts 1 through 9, it should be that oblique aberrations degrade the optical quality of the lens.
The following is an excerpt from “Pushing the Limits of Geometry in Lens Personalization,” a white paper by Dr. Jose Alonso, Dr. Daniel Crespo, Carolina Gago, Eduardo Pascual, and Eva Chamorro:
“Every optical system has aberrations: The eye, a magnifying glass, even the best compound lens microscope has some aberrations. There are different types of aberrations, and their values in a given optical system depend on its design, its manufacturing quality and especially how it is used. The optical quality of an ophthalmic lens is primarily affected by oblique aberrations, which is the name given in visual optics to the combination of oblique astigmatism and oblique power error. Although the calculation of oblique aberrations is complex, their effect is easy to understand: If the lens has been correctly manufactured and provides the right power for the main gaze position when the wearer aims with an oblique gaze, the power of the lens changes and, consequently, the refractive error is no longer correctly compensated. Fig. 1 shows the concept. The prescription can only be matched by the paraxial power of the lens if the gaze direction is perpendicular to its two surfaces. If the lens is tilted, because of the pantoscopic and facial angles of the frame, the lens will be affected by oblique aberration even in the main direction of gaze.”
Oblique aberrations depend on the object distance, meaning that oblique astigmatism and oblique power error differ for every gaze direction when looking at a distance object versus when reading. This illustrates the limitation of prior methods of oblique aberration corrections: If we optimize a surface so the lens performance is optimal for distance, in general, it will not be optimal at near and the other way around. For example, if we optimize a lens surface to compensate for the -0.33 D of spherical error at distance infinity, we will have an under correction of -0.46 D at near vision. If the surface is optimized to compensate for the oblique error at near vision, the lens will be overcorrected for distance vision. This dichotomy emphasizes an essential feature of Digital Ray-Path 2 Technology, which uses our natural ability to accommodate the negative oblique spherical component of sphero-cylindrical oblique aberrations.
FIG. 2 The effect of object distance on oblique aberrations
From time to time, we must pause and ask ourselves how all of the tech talk and lens claims relate to the desired outcome? For the ECP and the optical engineers behind the IOT Endless lens design, the goal is to deliver full fields of view, at all focal distances, with edge-to-edge clarity in single vision lenses. Our visual demands have changed with the introduction of digital devices, adding the demand for clear vision for a range of focal distances in object space. Our visual demands have expanded, and single vision lenses must improve to meet these demands. IOT Endless personalized single vision lenses with Digital Ray-Path 2 Technology deliver optimal customization for all working distances and focal ranges while improving visual quality for any gaze direction. What does the patient experience? Unprecedented visual comfort and optical performance in a single vision lens.