The Skinny on PAL Technology
Welcome to our continuing series of Credit Education Courses for Opticians.
This course has been approved for one hour of credit by the American Board of Opticianry. No fee is required for ABO credit.
Learning Outcomes: At the conclusion of this credit education course, participants should be able to:
1. Understand and explain how new internal PALs are manufactured.
2. Understand and explain internal PAL design features and benefits.
3. Precisely articulate internal PAL technology benefits to patients.
4. Conduct sales and marketing initiatives based on internal PAL technology.
Test procedures: Read the article and then click on the link below to take the test
This will open a new window with a test consisting of 20 questions. To receive ABO continuing education credit, respondents must correctly answer 16 of 20 test questions. Simply click on the best answer for each question and click the submit button at the end of the test. Your test answers will be automatically sent to Seiko Optical and we will send your CEC or notify you of test failure within 7 to 10 business days.
Note: Some states do not accept home study courses for continuing education credit. Check with the licensing board in your state to see if this course qualifies.
The Skinny on PAL Technology
Understanding how new internal PALs are manufactured and how the end lens product is created helps you present these PALs to patients in a precise, concise context.
External progressive addition lens technology dates back to 1907, the year the first external PAL was patented. In 1959, the first externally created PAL was ommercialized. Seiko pioneered the development of the first internal PAL in 1996, and Seiko Epson received the U.S. patent for this technology in 2000.
The Seiko Epson manufacturing process revolutionized PAL production by placing the progressive surface on the backside of the lens while keeping the front side spherical.
This in-depth continuing education course will detail each step of internal manufacturing. It will compare and explain internal versus external PAL technology while discussing the benefits of internal manufacturing, review recent developments in internal manufacturing, and fully explain how the end product--progressive addition lenses with 100 percent of the patient's prescription on the back surface of the lens--can be presented to patients in a simplified yet informative way.
PAL FUNCTIONALITY
Original PALs were front side design, meaning the progressive surface was on the front side of the lens. The original front side, hard PAL design often caused less stable images and created a smaller field of vision for wearers.
Asymmetrical and aspheric designs followed the development of hard PAL designs, then came aspheric and/or atoric backside surfacing.
Today, free-form processing, also known as digital surfacing, produces lenses that offer custom-made options for precisely enhanced vision. The design ceiling of internal PALs is pushed beyond the limitations of standard PALs; internal progressive design allows for an expanded field of vision and better image stability, which results in less distortion.
FRONT AND BACK
Simply put, internal progressive technology moves the progressive surface from the front side to the backside of the lens. When the progressive surface is moved from the front side to the backside of a lens, magnification differences between visual areas are greatly reduced and visual fields are significantly expanded. Placing the complex progressive surface on the len's back surface controls off-center astigmatism and power error.
Viewing distortion occurs when the size of an object appears differently through various areas of the lens. The external progressive addition lens technology dates back to 1907, the year the first external PAL was patented. In 1959, the first externally created PAL was commercialized. Seiko pioneered the development of the first internal PAL in 1996, and Seiko Epson received the magnification difference between areas equals distortion. Skew distortion in progressive lenses is basically an aberration that affects shape, which produces unwanted astigmatism. Size distortion in progressive lenses can cause viewed images to appear smaller (minification) or larger (magnification) than their actual size.
External PALs place the progressive power on the front surface of a lens, with the spherical or toric power placed on the backside of the lens. Base curve selection is designed for a large range of Rxs. This can adversely affect visual acuity and field of vision in all areas of the lens by creating distortion.
By comparison, internal PALs place the progressive power on the backside of a lens. This allows the front surface to be a perfect sphere. With internal PALs, a complex progressive surface is possible on the lens' back side, allowing total control of off-center astigmatism and power error. Internal PALs can be aspherically compensated for each Rx, including for each sphere, cylinder, axis and add power, including Rxs with prism.
Lens shape, lens power, and front curvature all factor into the cause and degree of magnification. Lens thickness, refractive index, vertex distance, and vertex power are also factors in magnification. Changes in magnification that create distortion in external PALs when the progressive power is built on the front side of a lens, are typically due to front curve changes and power changes in the lens.
With Internal PALs, the progressive power is built on the back surface of the lens, so changes in magnfication are due only to power changes, since there are no changes in the front curve. This significantly reduces distortion throughout the lens. By placing the progressive surface on the backside, closer to the eye, internal PALs expand the field of vision by working with eye placement closer to the lens itself to create a wider viewing section.
MANUFACTURING MATTERS
Lens designs come in two forms: as stock lenses or as semi-finished product. Stock lenses are purchased in the desired power, material, and base curve. Stock lenses come primarily in single-vision, as well as semi-finished.
Semi-finished single-vision lenses can be produced in higher powers than in a finished range. Semi-finished multifocal lenses come in PAL, bifocal, and trifocal options.
All semi-finished lenses are created using a series of glass molds. Glass molds must be made in set base curves, and multiple base curves are made to produce a variety of power ranges.
Once molds are created for single-vision or multifocal designs the material is cast in the mold to produce a semifinished lens. Semi-finished single-vision lenses are cast in base curve and material, and multifocal semi-finished lenses are cast in base curve, material, add power, and right and left eye format.
What's key to remember here is that traditional lenses are produced based on optimized lens blanks that are based on specific product ranges. This is working with pre-designed base curves, not spherical lens blanks. Lens availability is limited by the number of base curves available in any given product, material, and power.
Free-form processing is based on blanks, not base curves. When a free-form generator is combined with the appropriate optical software (point files), each lens is digitally created.
Each free-form created lens starts with a semi-finished single-vision lens. This requires fewer molds. Free-form processing can produce virtually any lens, including PALs, lenticular, slab-off, specialty segments, wrap (customized base curve) lenses, and single-vision.
Free-form software and equipment capabilities can place progressive curves on the front surface, back surface, or both front and back surfaces of a lens, depending on manufacturer requirements.
Processing typically includes aspheric and atoric design to improve optics and lens appearance. Aspheric design reduces oblique astigmatism to improve edge-to-edge visual clarity. Asphericity also flattens the lens' surface to improve cosmetics in both plus and minus powers.
Atoric technology basically moves aspheric surfaces to the back surface of a lens. By moving aspheric curves to the back of the lens, each curve is asphericized specifically to the curve used on the lens' front side. Atoric properties improve visual acuity by moving the correction closer to the eyes. Atoricity also significantly thins high-minus lenses.
Free-form generators manufacture these complicated curves via complete computer-driven operation. Point files guide the generators in surfacing each lens design, and each point file is only used once. This means that each lens has its own precise curves and can be customized to manufacturer parameters and each individual patient's requirements.
One step-by-step example of free-form processing includes a fully integrated free-form production line. The steps start-to finish include:
- Point-of-sale data entry is transmitted to the host.
- The host transmits the information to the Rx server.
- The server processes the information based on which free-form lens platform is selected and uses a particular manufacturer's point file.
- Lens production begins by blocking.
- The lens is processed in the generator.
- Next, the lens is polished on a flexible tool.
- This is followed by engraving (if the lens is not preengraved by the manufacturer) and cleaning.
- The final step is coating, e.g., hardcoat and/or antireflective.
Free-form generation utilizes cut-to-polish technology. Traditional generators use diamond wheels to form lenses, while free-form generators use a diamond tool that cuts surfaces with a single point.
Keep in mind that with conventionally designed PALs, base curves are designed for an entire Rx range centered on one specific power. These PALs will be totally accurate for only one spherical Rx over the entire Rx range.
Free-form equipment is highly accurate and allows for more precisely made prescriptions.
For example, when comparing exact PAL Rxs utilizing internal versus external PAL technology, conventional external PALs can offer only five spherical Rxs x 13 add powers. This creates only 65 exact PAL Rxs.
A look at the number of exact Rxs provided by one design in a specific index shows that an internal PAL design offers 69 spheres x 17 cylinders, equaling 1,173 powers.
Additionally, 1,104 powers x 179 cylinder angles + 69 spheres = 197,685 distance Rxs. And 197,685 distance Rxs x 13 add powers = 2,569,905 exact PAL Rxs, far exceeding the exact Rx availability of conventional external PALs.
DEFEATING DISTORTIONS
Barrel distortion can be caused by base curves that are too flat, while pincushion distortion may be caused by base curves that are too strong. This can occur even with aspheric designed PALs, since the base curve selection is limited.
As discussed earlier, conventional or front surface PALs will be totally accurate for one spherical Rx over the entire Rx range. This increases the likelihood off-center astigmatism, followed by off-center power error in aspheric external PALs.
Off-center astigmatism and power error are avoided when using an internal PAL by utilizing an aspheric design plus significantly increasing the optimal number of base curves that can be selected.
Internal PAL technology places a complex surface on the backside of the lens by fusing toric and progressive surfaces together into one Rx-specific point file. Free-form generators (lathe to polish machines) and the correct point file (optical software) digitally create each lens.
The point file combines curvatures utilizing a complex, integrated design process that does not overlay separate designs. This eliminates power error by combining curvatures instead of just adding distance and progressive powers. There is aspheric compensation for each Rx, offering over two million Rx combinations, billions if including prism Rxs.
Other internal PAL features include total control of offcenter (marginal) astigmatism and power error, accurate power throughout an expanded near viewing area, gradient cylinder control along the intermediate area, and wide, distortion-free clear distance vision. No two lenses are alike.
PRESENTING TO PATIENTS
While internal PAL technology can enhance the vision of every patient, some patients are primary candidates. Those want the best progressive technology on the market today, those who have visually acute and demanding professions such as engineers and doctors, and those with strong cylinder prescriptions are top candidates.
Free-form created lenses like internal PALs are a high margin item. They can build a practice's reputation for only offering the best products and services, and grow practice revenue. Using free-form created lenses helps differentiate a practice from the ordinary and helps the practice avoid price wars, buy-one-get-one, and other price-based sales and marketing strategies. These lenses also typically create a loyal clientele who return to the practice and refer others to the practice.
Personalized PALs are the product of intense, thorough market research and clinical studies, not unlike studies conducted by contact lens companies to verify and market their products. These studies often have a medical-visual focus as well as a practical, "how the lens is used" focus. Eyecare professionals can leverage these studies in their practice to help substantiate the cost of high-end technology to patients.
In addition to offering superior vision through free-form personalized production, free-form produced PALs should be sold in combination with premium anti-reflective coatings.
Many of today's free-form lenses are provided only with AR coatings. These premium hydrophobic and/or oleophobic ARs help repel dust, dirt, debris, and oils and are easy to clean and keep clean. In addition to touting better vision via free-form created personalized PALs, ECPs can promote premium AR as the best way to clear, comfortable vision. The frosting on the cake is the best vision.
When discussing internal PALs with patients, it's key to keep explanations informative yet simple. Here are several suggested dialogues:
Processing brief: "Free-form processing is computer-driven. Each lens is individually created to your specific visual parameters and prescription via computer programming and production."
Technology benefits:"With internal PALs, the progressive surface is on the back of the lens. This creates a wider field of vision, less distortion, and greater image stability. Each lens is customized to your exact prescription."
Only benefits: "These fully customized PALs deliver easy adaptation, precise power, an expanded viewing area in all parts of the lens, and a natural visual experience."
Converting a previously unsuccessful PAL wearer: "Improved image stability means no "swim and sway sensation. An expanded field of vision means you'll experience wide, clear vision at all distances." Converting a flat-top bifocal wearer: "In addition to the cosmetic benefits of no line, you'll gain an easier, wider, and more functional viewing area. You'll regain your intermediate vision."
Appeal to everyone: "Most of our patients tell us that they experience vision similar to regular single-vision glasses with these lenses."
Above all: Every presbyope in the practice should wear internal PALs and be able to relate their personal experiences with these lenses.
This concludes the article. Click on the link below to take the test.