A Short Course on Short Corridors
Here's what you need to know about the latest generation.
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 (PALs).

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.

PERFECT FIT

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.

DISPENSING SHORT- CORRIDOR PALS

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.