A Short Course on Short
Here's what you need to know about the latest
By Judith Canty, L.D.O., Alexandria, Va.
When American Optical introduced the AO Compact short-corridor lens, it sparked a virtual firestorm of research and development in short-corridor design. Emerging presbyopes no longer had to sacrifice stylish frames for the convenience and comfort of progressive addition lenses
PHOTO COURTESY OF SEIKO
Some years later, we now suffer from an embarrassment of riches. With numerous lens manufacturers offering at least one -- and often more -- short-corridor lens designs, the most difficult aspect of fitting patients with short-corridor lenses is deciding which design is best for them. Nevertheless, I believe it's possible to send a patient home with eyeglasses that enhance how he sees -- and looks.
PLAY THE MATCH GAME
Fitting short-corridor lenses is an art requiring some experience and a knowledge of basic techniques.
Fortunately, anyone can be a short-corridor artist. Here are some hints that can help you streamline the selection process and avoid expensive remakes.
Ask questions, then listen. First, I ask the patient what he needs his lenses to do, and then I listen carefully for key words and phrases. Does he work on a computer all day? Does he play sports -- or just watch? Do his hobbies require good near vision?
As I listen, I compare his needs against a mental inventory of available lens types and materials that may address those needs, fit his budget and get him into new eyeglasses in a timely manner. For example, an avid softball player may appreciate how B'Active lenses
(AO/Sola) reduce distortion in the edge of the distance zone. A habitutal computer user may do better with
Image lenses (Younger Optics), which have an expanded intermediate zone. And someone who spends a lot of time reading or doing close work could benefit from Solamax lenses
(Sola), which feature a wider near zone than other short-corridor lenses.
Say it again. Once the patient finishes speaking, I repeat his wants and needs to verify that what I heard and what he said is what he actually meant. As an eyecare professional, I know what kind of lens should work for this patient, but I try not to "pre-decide" until I have enough patient input.
PHOTO COURTESY OF SIGNET ARMOLITE
Choose a frame. By now, I usually have a good idea of which lenses will meet the patient's needs, but I'm not ready to recommend a particular lens yet. Instead, I invite the patient to choose a few frames, steering him away from styles I know will be too large or too shallow for his lenses.
Compile your data. Now, I put together everything I've learned about my patient and choose his short-corridor lenses. I begin by measuring the minimum fitting height of his frames. Right away, I may be able to eliminate certain lens manufacturers' styles or materials. For example, the recommended fitting height for Image short-corridor lenses is 18 mm. If the patient's preferred frame has a fitting height of 16 mm, he will have to choose another frame or I'll have to find another lens that has a comparable intermediate zone. Other lenses may be too expensive or available only by special order, but I usually can find a lens that fulfills my patients' needs.
Experience has taught me that a patient will be satisfied with eyeglasses made with short-corridor lenses only if his frames are properly positioned on his face. Ideally, he should be able to see through the distance, intermediate and near zones without making unnatural head movements or turning his head excessively. Here's how you can achieve a perfect fit.
Determine pupillary distance. Making sure your pupillometer is properly calibrated, measure the distance between the center of the patient's pupil and the bridge of his nose. Take separate monocular pupillary distance (PD) measurements so you can include facial asymmetry in your final calculations. For accuracy, hold the pupillometer against the patient's face as if he were looking through a pair of field glasses and record your measurements in split PD form, (i.e., 29/30).
Prefit the frame. Adjust the proper-sized frame so that it fits exactly as it will when the eyewear is finished. Remember, where you think the frame should fit and where the patient wants it to fit may be different. As you adjust the frame, take special note of the pantoscopic angle and other adjustments so you can them duplicate frame position in the final product. Finally, make sure you and the patient are at eye level with each other when you determine the fitting height to avoid parallax.
Mark the spot. Once the frame is properly adjusted, mark the demo lens with a fine-point marker to show the center of the patient's pupil. If the demo lens is missing, simply cover that portion of the frame with transparent tape to provide a marking surface.
Determine seg height. Measure the distance from the pupil mark on the lens to the deepest part of the frame with a PD ruler. Don't measure between the mark and the point directly beneath the mark -- more than one pair of lenses have been made incorrectly because the measurements were taken inaccurately.
Match the lenses to the frame. Verify that the lenses you've chosen will fit the final frame by aligning the central pupil mark with the appropriate point on the manufacturer's cut-out chart. If the lenses don't fit within the recommended area, don't try to make it work by fudging the decentration or seg
placement. Save everyone some aggravation and choose another frame. Your patient will appreciate your attention to detail and interest in his success as a PAL wearer.
You've completed your measurements, submitted your lab order and now, received the patient's new glasses. What happens next?
Begin the dispensing process where you finished the fitting process: By reviewing the lens design features that best address your patient's needs and wants.
Patients often become impatient with their new
PALs, not realizing they need to learn how their new eyeglasses work. Warn them that switching between old and new PALs will slow the adaptation process.
Have your patients test their lenses by reading sample text in various print sizes. Starting with larger print and moving toward smaller letters shows patients how the progressive corridor leads their eyes to the reading area. Let them know they may have to move their heads more than usual to look through the proper zones, but reassure them this will abate as they adapt to their new eyeglasses.
Schedule a 2-week follow-up visit to check frame adjustment, and for new wearers, evaluate the progress of their learning curve. (See "Troubleshooting" for common short-corridor problems and solutions.)
FUSING FORM AND FUNCTION
Technological advances in short-corridor lens production offer patients a functional -- and fashionable -- solution to their near vision problems.
Take the time to ensure proper fit without overpromising results and you'll be rewarded with satisfied patients who will share their positive experience with all their friends.
Ms. Canty is a licensed optician with more than 31 years in the optical business. She is a past-president and the current treasurer of the Opticians Association of Virginia.
- Know your product. Know what lens designs are available and in what materials.
- Listen to your patient's wants and needs, but remember that you're the expert and advise him accordingly.
- Describe the features that will best address those wants and needs without over-promising lens performance.
- Pay careful attention to frame selection and fit. Pre-
adjust the frame before taking any measurements.
- Carefully adjust the finished eyewear, referring to any notes you may have made during the fitting process.
- Instruct your patient on the proper care of her eyewear.
- Schedule a 2-week follow-up appointment to check progress and comfort.
Your measurements are accurate. The frame fits properly. The lenses are made to your specifications. So why is your patient still having problems with his new short-corridor lenses? Your first impulse may be to remake the lenses, but before you do, ask him a few questions.
Did his work environment change? Is he using a computer more or less than anticipated? Do flat surfaces appear curved or the reading area too small?
If the patient's complaints are nonspecific or he's generally dissatisfied with his eyeglasses, he may be suffering from buyer's remorse or reacting to comments made by friends or family. Resolving these problems may be as easy as listening to the patient and reevaluating his lens choices.
Sometimes a minor in-office adjustment can make a difference. For example:
- Changing the pantoscopic angle may "flatten" oddly curved surfaces
- Changing the frame's vertex distance or "face-form" may increase the intermediate and reading widths.
If you do have to remake the lenses, be sure you're requesting changes to address a particular problem. Remaking short-corridor lenses with no specific goal in mind is time-consuming and aggravating for everyone involved.
How Short is
Traditional progressive addition lenses
(PALs) have an average corridor length of 17 mm and require a 20-mm to 25-mm fitting height. Add in a minimum "B" measurement of about 31 mm and you have lenses that definitely aren't compatible with smaller frames.
Initially, some lens manufacturers tried to adapt to shrinking frame sizes by arbitrarily lowering their recommended minimum fitting heights. They justified this change by noting that this design reached about 85% of the add power at the new lower height. Unfortunately, 85% of a +2.00D add is +1.70D, which falls short of patients' expectations.
The next generation of short-corridor designs, with corridors between 13 mm and 15 mm, provide comfortable near vision fitting heights between 17 mm and 19 mm. This range still is the largest segment of short-corridor designs available in the greatest variety of lens materials.
The newest crop of super short-corridor designs range from 12 mm to 14 mm and accommodate 14-mm to 16-mm fitting heights. When working with such restrictive parameters, matching your patient's needs with the best lens design is critical to achieve optimal performance and comfort.
Optometric Management, Issue: November 2004