DEFINITY FAIRWAY Transitions adaptive sun lenses by Essilor offer cutting-edge features to help improve vision, sharpen colors, and contrast on the golf course.
Most eyecare professionals (ECPs) don’t realize that the majority of progressive addition lenses (PALs) are designed around average eye parameters—not for the individual or specific patient. The recent trend of lens manufacturers is to customize the design of a lens for the exact measurements and requirements of the patient sitting in front of you rather than the average patient. This means that ECPs can now deliver customized lenses that include the personalized parameters each patient requires. Customization is achieved using prescription, position-of-wear, and frame size.
PRESCRIPTION Today’s advanced lens design software combined with free-form surfacing makes it possible to customize a progressive lens design based upon the unique prescription requirements of each wearer. By optimizing the optical design for each patient’s prescription, lens aberrations are virtually eliminated. Patients can also experience the widest fields of clear vision, regardless of prescription. Fields-of-view are often more symmetrical too so the binocular vision of the lenses is improved.
POSITION-OF-WEAR Position-of-wear is the position of the fitted lenses on the patient’s face in their eyewear. Additional measurements are required from the ECP for this type of customization.The measurements include pantoscopic tilt, face-form or wrap, and vertex distance. Check with the lens manufacturer to see which parameters their lens requires. Each of these parameters has an effect on the visual experience of the patient. If these parameters are different from the position of the lenses during the refraction, the power supplied to the patient in the finished lens will be different from what the refractionist intended. Admittedly, most patients with weaker powered Rx’s and minor changes will notice little if any effect in their vision from these compensations, but in higher powered Rxs with higher add powers, these parameter changes can result in power errors that patients detect.
Prescriptions are determined using a refractor (phoropter) or trial frame with lenses that are positioned perpendicular to the patient’s line of sight with no pantoscopic tilt. Eyewear frames generally have 8° to 12° of pantoscopic tilt. Tilting of the lenses (panto and wrap) introduces unwanted power errors in the lens prescription. These unwanted power changes can reduce the optical performance of a progressive lens, particularly through the central viewing zones. If the patient’s vertex distance, pantoscopic tilt, and face-form tilt are supplied, these factors can be compensated and patients will get lenses customized to provide them with the best vision.
Each MyStyle lens from HOYA is created using ‘Intelligent Design by Extensive Analysis’ (iDEA) technology.
Lenses compensated this way will be supplied in 0.01D powers. This means that it is not possible for the ECP to verify them. Make sure you use a trusted lab for this kind of work since you will need to take their word for it that the lens powers are correct.
FRAME FACTORS Some lenses automatically compensate the corridor length based on the vertical dimension (the B measurement) of the frame. You might call these “smart lenses.” The idea is to provide the basic zone sizes of a design in different depth frames. For example, let’s assume that a particular free-form PAL used 50% of its optics to deliver distance vision, 20% for intermediate, and 30% for near viewing. If this lens was placed in a deep frame and a shallow frame, those dimensions would not stay the same in a traditional lens because the lower portion of the lens would be cut away in a shallow frame. Some customized lenses alter their configuration in order to essentially supply similar zone sizes, no matter what the B measurement is. This ensures that the patient receives the intended design features. Of course, the optician can override this feature and order a specific fitting height if desired.
SOME EXAMPLES Each MyStyle lens from HOYA VISION CARE, North America, is created using “Intelligent Design by Extensive Analysis” (iDEA) technology. This is a process that goes beyond merely incorporating the prescription and frame positioning to include a comprehensive consultative process that determines all the parameters needed to create the patient’s ideal lens.
The Zeiss Individual from Carl Zeiss Vision benefits from wavefront correction.
Shamir Insight Inc.’s Autograph II® progressive lenses use Shamir’s patented free-form manufacturing techniques and EyePoint Technology® during the design stage to create customized lenses. EyePoint Technology simulates the human eye and traces every angle of vision in each optical zone and prescription range, thus improving clarity for the greatest field of view and best vision for the patient.
WAVEFRONT LENSES The most advanced customized lenses are those that incorporate wavefront technology to design lenses that will correct Higher Order Aberrations (HOAs). See “Wavefront Optics and the Eye,” p.60. Three lens manufacturers are currently leading the way.
Ophthonix, Inc. manufactures wavefront-guided iZon lenses that address the symptoms of HOAs of a patient’s eye by measuring the lower order (LO) and HOA and determining the patient’s wavefront-based prescription with the company’s Z-View® Aberrometer. The instrument produces an iPrint® that includes both LO and HOAs information — the wavefront-based refraction, which is incorporated into the iZon lenses.
Carl Zeiss Vision Inc. has several lenses that benefit from wavefront correction: Zeiss Individual™; Zeiss Individual Single Vision, GTD 3D, GT2 3DV, and Zeiss 3D Single Vision; and VSP Reveal™ Freeform. Its proprietary i.Profilerplus® is a combination aberrometer, autorefractor, and topographer. Zeiss’ iScription® software combines the subjective refraction and the aberration data to create a prescription that is balanced for the patient’s range of pupil sizes.
According to Essilor of America, Inc., Varilux Physio Enhanced™ eyecode™ and Varilux Ipseo IV™ eyecode lenses are the only PALs that take the patient’s
Autograph progressive lenses use Shamir’s patented free-form techniques and EyePoint Technology to create customized lenses.
unique Eye Rotation Center (ERC) into account and also measure the patient’s natural head posture, visual behaviors, and position-of-wear. Using W.A.V.E. Technology 2™, Essilor’s Varilux Physio Enhanced lenses are created with four additional factors (age, working distance, light conditions, and prescription) in the design to provide a more customized HOA lens solution.
TASK-SPECIFIC LENSES DEFINITY FAIRWAY™ Transitions® adaptive sun lenses by Essilor offer cutting-edge features to help improve vision, sharpen colors, and contrast on the golf course. DEFINITY™ PALs feature the Ground View Advantage™ that gradually decreases power below the add at the bottom of the lens. What results is clearer vision when patients look down.
Seiko Sportswear Transitions sun lenses from Seiko Optical Products of America, Inc. use a proprietary tint that filters light evenly throughout its activation range to provide excellent color contrast separation, depth perception, and color recognition in all light conditions; it’s available in all Seiko free-form PALs.
Why recommend lenses that are designed based on average eye measurements when you can design one that’s customized for your patient’s eyes and the way they’ll use the lens? As the free-form revolution continues, more lenses will be designed this way.
Randall L. Smith is the Opticianry Program Director at Baker College in Jackson, MI.