|Shamir’s premium product, Autograph III, includes EyePoint Technology III and updated lens design software.|
|Surmount from Seiko has a variable inset based on distance Rx, PD, and customized near reading distance.|
|Essilor’s latest lenses, the Varilux S Series, address the problem of binocular vision.|
|Augen’s Trinity Spacial features ultra-wide intermediate and distance zones.|
Premium free-form progressive lenses offer advantages that their lower-tiered brothers don’t have.
Modern design and manufacturing processes have given the optical industry free-form lens technology that has revolutionized ophthalmic lenses to the delight of patients and eyecare professionals (ECPs) alike. The popularity of this technology has brought with it a blizzard of designs and tiering of lens features.
To get the most from free-form PALs, look to the premium versions from companies like Augen Optics; Carl Zeiss Vision, Inc.; Essilor of America, Inc.; HOYA Vision Care, North America; Nikon Optical USA, Inc. (with its SeeMax family); Seiko Optical Products of America, Inc.; Shamir Insight, Inc.; and Signet Armorlite, Inc. because they have the most advanced features and benefits. Here’s a look at what you can expect from premium free-form PALs.
All free-form PALs use aspheric and/or atoric curves. Aspheric curvature also facilitates flattening a lens’ profile and reducing lens thickness for improved cosmetics. In addition, it makes lenses lighter, which improves wearer comfort.
Premium free-form PALs have more precise powers which are produced using the lens design and surfacing aspects of the free-form process. They are accurate to a power of 0.01D and one manufacturer claims a surface accuracy of 0.1 micron. This precision is one reason patients often report that their new free-form PALs are clearer than their previous standard designs. Lens aberrations are also reduced dramatically from traditional designs and clear zones are often wider and/or more usable.
VARIABLE CORRIDOR HEIGHTS Conventional PALs limit wearers to one of two basic corridor lengths: standard (also known as long) and short. These two configuration types are unable to provide optimal positioning of the lens’ optics for all patients in all frame shapes and sizes. As a result, some wearers experience truncated reading areas, mis-positioned zones, or distorted viewing.
Some manufacturers design their PALs with variable corridor length. Based on the corridor length utilized, the lens’ design essentially expands or contracts to make the best optical use of the lens within the frame. The result is wide, balanced fields of vision customized for each frame. One manufacturer offers fitting heights from 13mm to 35mm in 0.1mm step increments and some have similar offerings. Other manufacturers handle this issue by supplying multiple fitting heights.
The concept of “position-of-wear” (POW) is that a lens’ power and optical performance is affected by its position in front of the eye as it is worn in the eyeglasses. The factors that affect POW include pantoscopic tilt, face-form (wrap), and vertex distance. Spectacle prescriptions are traditionally determined using a refractor or trial-frame lenses that are positioned perpendicular to the wearer’s line of sight during the examination and sit farther away from their eyes than the lenses in their eyeglasses. Spectacle lenses mounted in a frame are tilted, curved, and sit at a different distance from their eyes than during the refraction. These variations from the exam chair affect the performance of the lenses in its POW. That’s why premium PALs require POW measurements and are compensated for them.
When taking measurements for POW-compensated premium PALs you’ll need the standard monocular PDs and segment heights as well as vertex distance, pantoscopic tilt, and face-form tilt. If you don’t supply these measurements, the surfacing program for the lenses will supply data from a normative database instead.
Conventionally designed PALs have a fixed inset. While this might be acceptable for flat-top bifocals that use a 35mm horizontal segment window, it’s not ideal for progressives that have a modest corridor that’s completely clear. To maximize the corridor’s usefulness, both eyes must track down the center of their respective corridor. This provides the widest field-of-view and makes the lenses easier and more comfortable to use due to overlapping clear binocular fields.
In order to accomplish this, some lenses use a variable inset strategy. This is because the prismatic effect, experienced as the eye converges and tracks down the lens, forces it to look at a location differently from the one illustrated using simple geometry because it disregards this prismatic effect. As the lens powers and the add become stronger, the variance between the actual points of gaze and the estimated “geometric” ones can be surprisingly high. Some companies vary the inset from 0.0mm to 5.0mm in 0.1mm increments giving you a possible 306 different insets depending on the patient parameters that include Rx (distance and add power), PD, vertex distance, pantoscopic tilt, and face-form.
A higher-order aberration (HOA) is a distortion acquired by a wavefront of light when it passes through the eye’s refractive components (tear film, cornea, aqueous humor, crystalline lens, and vitreous humor) that have irregularities that may not be corrected by conventionally surfaced lenses. HOAs can affect vision, even if the patient’s prescription eyeglasses correct their refractive error. The abnormal curvature of the cornea and crystalline lens, scarring of the cornea from eye surgery, trauma or disease, cataracts, and dry eye can be the sources of HOAs.
Free-form technology and progressive lens designs from two lens manufacturers in the past have offered patients lenses that address HOAs and can provide sharper vision, especially in low light situations. Ophthonix, Inc. introduced the iZon™ wavefront-guided lens in progressive form in 2006 and that same year Essilor launched a wavefront-guided progressive with Varilux‘ Physio‘ and Varilux Physio 360°.
HOA lenses improve contrast so it’s common to hear patients mention that they see things more sharply, crisper, and bolder, and that they don’t see ghost images around lenses or flare and glare around lights at night. This makes them ideal for nighttime driving and other low light situations.
Binocular vision is a vital factor in a patient’s visual comfort. Visual confusion and discomfort can result when eyes that are capable of binocular vision are confronted with situations that cause one eye to blur, disrupting the binocular function. Essilor’s latest lenses, the Varilux S Series™, address this problem using SychronEyes Technology™ and Nanoptix Technology™. SynchronEyes Technology coordinates the design of the left and right lenses to ensure that wherever the patient looks, the left and right lenses provide similar quality images. The result is optimized binocularity, allowing both eyes to function as one visual system.
Instead of looking at a lens as having a single continuous curve, Nanoptix Technology is designed to consider the lens as thousands of optical elements. The length and position of each element can be controlled in order to meet the precise requirements of the design and the power. According to Essilor, this virtually eliminates the swim effect.
Premium free-form PALs provide the most advanced features to patients for clear, distortion-free, and comfortable vision. Why recommend anything else?
Randall L. Smith is the Opticianry Program Director at Baker College in Jackson, MI.
|WHERE TO FIND IT:|
866-284-3611 • augenoptics.com
|Carl Zeiss Vision, Inc.
800-358-8258 • zeiss.com/lenses
|Essilor of America, Inc.
800-542-5668 • essilorusa.com
|HOYA Vision Care, North America
877-528-1939 • hoyavision.com
|Nikon Optical USA, Inc.
877-767-8033 • nikonlenswear.us
|Seiko Optical Products of America, Inc.
800-235-5367 • seikoeyewear.com
|Shamir Insight, Inc.
877-514-8330 • shamirlens.com
|Signet Armorlite, Inc.
800-950-5367 • signetarmorlite.com