BACK TO BASICS

NECESSARY MEASURES

This Back to Basics article explains why accurate measurements for progressive lenses can control remakes

BY JENEAN CARLTON, ABOC, NCLC

Progressive lenses are wonderful visual tools for patients. But when not made absolutely perfectly, they don’t provide the vision they should, and need to be remade. Remakes cost manufacturers, labs, and practices lots of hard-earned dollars.

Laboratories may offer remakes at “no charge” to their customers, but these lenses aren’t really free. How could they be? Wholesale laboratories have to make a profit to survive just like any other business. Remakes cause lens prices across the board to be high, especially when it comes to PALs.

Premium progressive lenses are advanced, mathematically complex, and expensive. A wholesale pair of premium PALs fabricated in 1.67 index with Transitions costs somewhere around $300. Add AR treatment and the wholesale cost jumps to about $380.

These lenses offer patients the latest-and-greatest lens design, treatments, and high-quality vision, but at a premium price.

A target remake percentage for the average practice is 5%, and it’s a do-able goal for most offices. Unfortunately some practices have a remake percentage as high as 25%. Who’s to blame for so many remakes? There will always be a percentage of remakes due to Rx changes, but that doesn’t account for the vast majority of PAL redos. Most progressive lens remakes are due to measurement errors made by staff members—primarily opticians and technicians.

Incorrect PDs and segment heights account for a great majority of measurement errors. The best way to lower the percentage of remakes in a practice is to teach staff how to take accurate measurements every time. The goal is to obtain exacting measurements on the initial patient visit. After all, patients don’t appreciate being asked to return to the office to re-take measurements.

Some measurement devices are free-standing kiosks. (Essilor’s Visioffice 2 system)

Some measurement devices are available in kiosks as well as handheld systems (Zeiss’ i.Terminal mobile)

Read on to learn the importance of each progressive lens measurement and how to reduce the number of remakes in the practice.

FRAME ISSUES

SIZE. The best frame choice for PAL wearers is one that offers a “B” measurement deep enough to house the entire length of the progressive corridor. Frames with “B” measurements that are too narrow can result in the near zone being edged off in the finishing process.

Opting for frames with a deep “B” measurement allows ample room for the full length of the progressive corridor and ensures that the near zone remains complete.

NOSE PADS. Frames with adjustable nose pads are also a good idea for progressive wearers as nose pads allow dispensers to make minor adjustments in the height of the progressive corridor. If the fitting height of a PAL is too low, moving the nose pads closer together raises the segment height. If the segment height is too high, broadening the nose pads slightly will lower the progressive corridor and allow patients to use their eyewear more comfortably.

ADJUSTMENTS. An excellent way to decrease remakes is to adjust the frame prior to taking any measurements. Before taking any measurements, adjust the frame for the patient just as you would when dispensing the finished eyewear. With progressive lenses, the frame should be fitted as closely as possible with a maximum vertex distance of 12-14mm so the patient can appreciate wide fields of vision through the distance, intermediate, and near zones.

Many iPad-based apps take measurements as well as handle lens demonstrations. Shown here: HOYA Vision Care’s Spectangle Pro

Many iPad-based apps can handle myriad measurements in one click. Shown here: otto from VSP Optics Group

PATIENT MEASUREMENTS

It is vital that dispensers measure the patient’s pupil and reading zones exactly. It is the only way to ensure proper vision through PALs.

MONOCULAR PD. The monocular PD is the distance from the center of the pupil to the center of the patient’s bridge. The monocular PD indicates the horizontal position of the PAL corridor.

It is necessary to properly align the optical center of the lenses with the patient’s visual axis. If the monocular PD is incorrect for either eye, the patient will have difficulty gaining one fused image when looking at objects through their progressive lenses. They will also have difficulty seeing clearly through the intermediate and near zones.

When viewing objects at near, the eye travels down the narrow progressive corridor until it reaches the Add power located in the near zone. It’s imperative that the monocular PD be accurate so the corridor is positioned exactly in front of the visual axis. The easiest and most accurate way to obtain the monocular PD is with a Corneal Reflex Pupillometer or, if available, with a digital measuring device.

MONOCULAR SEG HEIGHT. The monocular segment height is the distance in millimeters from the center of the pupil to the very bottom edge of the lens opening. This measurement is critical as it establishes the vertical placement of the progressive corridor in front of each eye. It’s important to measure the segment height for each eye, as one eye may be higher than the other.

Be sure to begin your measurement at the center of the pupil, not from the bottom of the pupil or lower. Measuring from the center of the pupil down ensures that patients will be able to easily read through the near zone of their progressive lenses. If a digital measuring device isn’t available to take this measurement, use a marker to dot the center of each pupil and measure from the center of the dot to the very bottom of the lens opening.

VERIFY CUTOUT

Dispensers will always need to verify that the lenses will cut out properly by using a cutout chart supplied by each manufacturer. Ask your lab for these charts or download them directly from the manufacturer’s website.

It’s unusual for a job to not cut out with modern lens fabrication methods. However, it’s a good habit to check that the lenses will be large enough for the order during a patient’s initial visit. Doing so may prevent patients from having to return to the office to select a smaller frame.

FRAME MEASUREMENTS

In order to get the highest performance from premium progressive lenses (with designs that can be personalized for each patient’s measurements), it is important to take several measurements relative to how the frame sits on the patient’s face.

PANTOSCOPIC TILT. A frame has pantoscopic tilt when the bottom of the frame front angles towards the wearer’s face and the top of the frame front is away from the face. The ideal pantoscopic tilt angle is 7-12 degrees. Pantoscopic tilt brings the near zone closer to the eye and increases the field of view through the reading area of the progressive design.

VERTEX DISTANCE. The vertex distance is the distance in millimeters from the steepest curve of a patient’s cornea to the back surface of a lens. The average vertex distance is 12-14mm.

The lenses mounted in a phoropter are positioned at 12-14mm away from the patient’s eyes during exams. Therefore, in order for the patient to experience the same visual acuity as achieved during the exam, it’s important to position the glasses at this same distance from the eyes.

Labs need to know the vertex distance measurement so they can adjust the lens power if necessary, particularly when higher-powered lenses are prescribed.

A distometer is an old-school tool used to measure the vertex distance of lenses. Most digital measuring devices are capable of measuring the vertex distance as well as other pertinent measurements needed for progressive lens orders.

WRAP ANGLE. The wrap angle is often referred to as the faceform angle, panoramic angle, or even frame wrap. This angle indicates the amount of curvature a frame has towards the patient’s face. Frames with more faceform will curve more closely towards the wearer’s face, while a frame with less faceform has a flatter frame front.

Frames should have a slight degree of wrap angle. To increase the amount of faceform, use both hands to apply pressure at the bridge and move it slightly inward. To decrease the amount of faceform, place both hands on the bridge area and gently move the frame front outward. With plastic frames, it’s necessary to heat the frames first before attempting these adjustments.

Adjustments to the faceform angle can help patients with peripheral distortion problems. Try increasing the amount of faceform curvature slightly for patients experiencing discomfort with the peripheral area of their lenses.

DIGITAL MEASURING DEVICES

The measurements needed for PALs such as monocular PD, vertex distance, pantoscopic angle, faceform wrap, and segment height are too often incorrect due to errors made by dispensers. The bottom line is that taking these measurements manually, even in the most skilled hands, is difficult because patients may move their heads, and eyes, while dispensers attempt to take their measurements.

Some iPad apps don’t need the frame calibration hardware to get the measurements. Shown: Shamir Spark from Shamir Insight

Doesn’t it make more sense to put an end to these errors all together by incorporating the use of digital measuring devices in your practice? This way the chance of measurement errors occurring is greatly reduced, and that means fewer remakes for your practice and a higher level of patient satisfaction.

Dispensers can obtain accurate measurements for every patient, every time, by using a digital measuring device. There are many devices on the market now—from kiosk devices to hand-held devices that are iPad- or tablet-based—that will change the way your practice takes measurements and will have a positive impact on your lens remakes (see sidebar below).

When your practice can reduce its number of remakes, your patients are happier, your lab (if you use one) is happier, and your revenue stream is happier.

Lens Measurements

Taking accurate measurements for each progressive order is necessary to limit remakes and provide patients with good vision. Try to find all of the answers to each statement below relating to measurements for PALs.
For the solution, see p. 58.

ACROSS

4. The monocular PD is the distance from the center of the pupil to the center of the ______ _____. (2 words)

7. The_____ _____height is the distance in millimeters from the center of the pupil to the very bottom edge of the lens opening. (2 words)

11. Pantoscopic tilt brings the near zone closer to the eye and increases the field of view through the _____ _____of the progressive design. (2 words)

13. The ideal _____ _____angle is 7-12 degrees. (2 words)

14. Adjusting the frame _____ to taking any measurements is a way to cut down on remakes.

17. The best frame choice for PAL wearers is one that offers a “B” measurement deep enough to house the entire length of the _____ _____. (2 words)

20. Incorrect PDs and ______ ______ are by far the most common reason for remakes. (2 words)

24. If the monocular PD is incorrect for either eye the patient will have difficulty gaining one _____ image when looking at objects through their progressive lenses.

25. The way to lower the percentage of remakes in a practice is to teach staff how to take _____ _____ every time. (2 words)

26. With progressive lenses, the frame should be fitted as closely as possible with a maximum _____ _____ of 12-14mm. (2 words)

27. It’s imperative that the monocular PD be accurate so the corridor is positioned exactly in front of the _____ _____. (2 words)

DOWN

1. When viewing objects at near the eye travels down the narrow progressive corridor until it reaches the _____ _____ located in the near zone. (2 words)

2. The easiest and most accurate way of obtaining the monocular PD is with a Corneal Reflex Pupillometer or, even better, with a _____ _____ _____. (3 words)

3. The vertex distance is the distance in millimeters from the _____ curve of a patient’s cornea to the back surface of a lens.

5. Unfortunately some practices have a _____ _____ as high as 25%. (2 words)

6. Frames with “B” measurements that are too narrow can result in the near zone being edged off in the _____ process.

8. Opting for frames with a deep “B” measurement allows ample room for the full length of the progressive corridor and ensures that the _____ _____ remains complete. (2 words)

9. Frames with _____nose pads are also a good idea for progressive wearers.

10. Wholesale laboratories have to make a _____ to survive just like any other business.

12. Before taking any measurements adjust the frame for the patient just as you would when dispensing the _____ _____. (2 words)

14. During an examination the lenses mounted in a _____ are positioned at 12-14mm away from the patient’s eyes.

15. If the fitting height of a PAL is too low, adjusting the nose pads _____ _____ will raise the segment height. (2 words)

16. Adjustments to the faceform angle can help patients with _____ distortion problems see better through their lenses.

17. The wrap angle is often referred to as the faceform angle, _____ _____, or even “frame wrap”. (2 words)

18. Dispensers will always need to verify that the lenses will cut out by using a _____ ______supplied by each manufacturer. (2 words)

19. Get accurate _____ for every patient, every time, by using a digital measuring device.

21. The monocular PD indicates the __________ position of the PAL corridor

22. Most progressive lenses are remade due to _______ errors made by staff members.

23. _____ don’t appreciate being asked to return to the office to retake measurements.