Merchant Processing Services

There are many progressive lenses available for the eye care professional. With more than 200 lens designs to choose from, it is imperative that the ECP narrow down the choices to what works best for his or her practice, as well as the patient. The best way to do this is to select a lens that is easy for the ECP to fit and dispense and is easy for the patient to wear. Getting the Perfect Fit The most common problem with progressive lenses is not with the lenses themselves, or even with adaptation problems. The most common reason why a progressive doesn't work for the patient is because of optician error. The most common optician errors are due to improper fit. These can be minimized or eliminated by keeping the following tips in mind. Selecting the Frame The perfect frame will be lightweight and well fitted to reduce slipping. Adjustable nose pads are best to allow for fine tuned adjustment. The eyes should be well centered with an adequate B measurement and the overall width should not exceed the widest point of the patient's features.

Frame Adjustment
Always adjust the frame prior to taking the lens measurements. Adjustments should be made just like they would be at dispensing. First, have the patient place the glasses on his or her face in the position in which it is normally worn. Now, look at the patient and observe how the frame fits. A proper fitting frame should have the following characteristics, if not make the necessary adjustments.

• The nose pads should lay flat against the bridge of the nose, exhibiting the proper splay angle to prevent digging or pinching on the delicate skin of the nose and inner eye. 
  

• The frame front should have a pantoscopic tilt between twelve and fifteen degrees because you want the reading area as close to the eye as possible to increase the reading width. Tilt changes the effective sphere, cylinder and axis of prescriptions, and an excessive amount of pantoscopic tilt can cause the patient to experience blurred vision and eye strain. There should be two degree's of pantoscopic tilt for every one millimeter that the visual axis is above the datum line.
  

• The frame should have the proper face form wrap. This allows the frame to follow the natural curve of the face and enables the patient to have a wider field of view in the distance through increased peripheral vision. The same ratio applies here. For every one millimeter of decentration the frame should have two degree's of face form.
  

• A close fitting vertex distance is important to prevent visual distortion. A proper vertex distance not only allows the patient to get the full benefit of the width of the lens corridors, but it is of extreme importance to patients who have prescriptions in the higher ranges. Changes in vertex distance change the effective power of the lens. The temples should be angled properly and well fitted at the temple bend and behind the ear. 

By pre-adjusting the frame, any fitting problems will be discovered early on and prevent the lens from being placed in an ill fitting frame. It will also minimize any fitting height errors that may result from measuring a pair of glasses that are fitting uneven, too tight or loose or exhibiting an "X" ing problem.

Taking the Fitting Height
Eye care professionals should position themselves in front of the patient at eye level. Have the patient look off into the distance and with a marking pen, dot the center of the patient's pupil. Remove the glasses and draw a one inch straight line across the dot. Next, have the patient put the glasses back on to verify where the fitting height is. The patient should be looking through the line. Now ask the patient to walk around the dispensary and then resume sitting. Observe the patient's posture and stance in relation to the fitting height. Adjust the fitting height if necessary. Always verify the fitting height in this manner, even if you have the previous fitting height, because a patient's posture and stance may have changed since the previous fitting as well as the vertex distance could be different, altering the segment position.

An alternate technique is to use a ruler and a penlight. This technique is similar to taking a PD with a ruler and a penlight, but the ruler is held vertically. You position yourself at eye level to the patient and have them look at the penlight which is next to your eye. Using your free hand or a segment measure, measure from the bottommost part of the frame to the corneal reflection. This will be their segment height precisely. 

One should note that a patient will normally have an uneven fitting height. Make sure that the uneven height is ordered. If it is not, the patient may exhibit distorted vision in each eye. This could be the result of:

• one eye looking through the intermediate portion of the lens corridor while viewing the distance if both fitting heights are placed at the height of the higher eye

• one eye not reaching maximum add power if the fitting heights are set to the height of the 
  lower eye

• uneven MRP causing a prism imbalance that may cause a problem when converging to near

Pupillary Distance
Monocular PDs should always be taken when fitting a patient with a progressive lens. The preferred way to measure the PD is using a corneal reflection pupilometer. This is the preferred method because they help eliminate parallax errors, they work very well on very dark irises, and are easy to develop accuracy with. The first step is to adjust the working distance dial to the distance setting which is infinity. Sitting across from the patient, place the pupilometer on the patient's nose with the forehead bar centered against the forehead. Ask the patient to look into the light and then move the paddle to the center position so that both eyes are open. Move the hairline to bisect the corneal reflex of each eye. The monocular PD is then displayed on the top of the pupilometer. As a side note, you only use the paddle to occlude one eye at a time when the patient is having trouble fixating with both eyes such as when they have strabismus. If you occlude one eye, the other will take up fixation and you can get a more accurate measurement.

To verify that this measurement is accurate, the machine should be calibrated at least weekly. In order to verify accuracy, you should set the PD to 32/32 and place a ruler against the hairlines. The measurement should be 64. If it is, then the calibration is complete. If it is incorrect, note the difference, measure again at 29/29 and 35/35. If the pupilometer is off the same amount in each case, remember to adjust the measurements taken to correct them until the pupilometer can be sent for calibration. If there is no consistency, stop using the pupilometer and send if off for repair. 

If the pupilometer is unavailable, the ECP can measure the PD by measuring from the center of the bridge to the pupil dot that was placed on the lens when determining fitting height or utilize the corneal reflection method to the middle of the bridge.

Taking additional measurements
Some measurements are required for the newer, free form lens designs. These are:

• Face form wrap – Frame wrap can be determined using a face form wrap protractor. This is a simple chart that you can get from many lens manufacturers.
  

• Vertex distance – Vertex distance can be measured using a very accurately with a distometer.
  

• Pantoscopic tilt – Lens manufacturers can usually provide a tool to help measure pantoscopic tilt. One such tool is the Zeiss Individual™ Panto and Vertex Tool. When taking the pantoscopic measurement using this tool, it should be taken vertically, parallel to the face and perpendicular to the patient's forward facing gaze. 

The ECP should also verify that the selected lens will cut out by utilizing the cut out chart before submitting the order to the lab. This will prevent a patient from losing add power, having to come in for a frame restyle, or from having to issue the patient a patient satisfaction refund.

The Art of Dispensing the Lens
Verifying the power

Proper lens dispensing begins at the verification process. Depending on the type of progressive chosen, the ECP may have to follow the manufacturer's recommendations on how to verify the progressive. Some of the computer generated, free form lenses need to be verified using the company's compensated prescription that they send back to the dispensary with the finished glasses. This is because the older technology of the focimeter, or lensometer, does not verify the advance design of these lens designs very well. If this is the case for the progressive lens that is chosen, be sure to follow the directions carefully. 

In other cases, verify the lens as normal.

• Mark up the progressive using a lens cut out chart, if the lens was not received with markings already in place.
  

• Verify the distance prescription in the distance circle. This is the best place to check the power.
   

• Verify the near prescription. The easiest way to verify the near prescription is to utilize the engravings present on the lens but it is best to verify the prescription via the lensometer. If you use the near circle, be sure to place the front surface of the lens against the focimeter, verify the distance first, and then verify the add power.
  

• Check the prism at the Major Reference Point (MRP). This is also called the Prism Reference Point (PRP). All progressives have a prism ground into the lens for thinning purposes. This helps reduce the overall weight of the lens and improves the appearance of the progressive. The prisms are usually an equal amount of vertical prism so therefore there are no prism imbalance or convergence issues to affect the patient. Therefore, this prism would never be seen in the lensometer. The MRP or PRP is to either verify the amount of prism that was prescribed or to determine that no prism has been mistakenly induced.

Double checking the fit
After adjusting the frame to fit the patient comfortably, make sure that the fitting cross is fitting at the center of the patient's pupil. Make minimal adjustments if necessary to ensure that the progressive is centered properly. If there is a centration problem with the lens that cannot be corrected and still maintain a comfortable frame adjustment, then remake the lens. Centration problems will result in a narrowed field of view, especially at the intermediate area. It will also cause the patient difficulty in transitioning from the distance to near portion of the lens.

Educating the Patient
Once the patient has his or her glasses on, reiterate how a progressive lens works. Explain to the patient the limited peripheral view areas and how to lower the eyes, not the head, in order to see through the corridor properly. Also, demonstrate the head movements that are necessary (moving the chin) to see everything clearly. These are best analyzed by utilizing a reading card to display the near and intermediate areas of view and having the patient look off into the distance.

Making it easy to wear
Most of today's progressive are very easy for the patient to adapt to, especially when care is taken during the measuring and dispensing process. However, sometimes issues occur. This is when trouble shooting must be done.

• Verify, verify, verify – This means double check everything.

• Ascertain what the patient is having difficulty seeing. The general statement "I can't see anything out of these glasses" can mean that the patient is having difficulty reading, working on the computer, or driving.

• Use active listening skills to help narrow down the problem, i.e. "I have to lower my chin to see in the distance," may mean a fitting height that is too high due to an improper measurements or adjustments.

• Determine if there is a common adaptation issue that is creating the problem such as going from a lined bifocal to a progressive or a significant change in lens design or prescription.

• Is the patient the problem – do they have realistic expectations, do they have the ability to focus or converge properly, or do they know who how to use the lens?

If all of these issues have been looked at and eliminated as the causal factors for the patient's problems, then refer the patient back to the referring physician. At this point the problem is either medical or an issue with the refraction.

Giving the patient the best experience
Patients go to a practice because they expect the best, and it is the job of the eye care professional to give it to them. It is imperative that the patient be offered the best in knowledge and fitting skills. When an eye care professional takes the time and care to get it right the first time, it really makes an impression on the patient, enhances the ECP's reputation, increases the patient base for the practice and significantly reduces the amount of spectacles that need to be re-made.

With contributions from: Brian A. Thomas, P.h.D, ABOM

Carrie Wilson
BS, LDO, ABOM, NCLE-AC