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Module 20 Section 2 |
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Module 20: |
Handling Glasses Complaints | ||
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Section 2: |
Solving Specific Problems | ||
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Progressive lenses, any complaint Cannot see the computer screen well Can only read with one eye, or closes one eye to read The eyes don't focus at the same distance at near Distortion, including slanting lines Headache, eye soreness, eyestrain Double vision when looking straight ahead Double vision when looking through a lens edge Double vision or discomfort only when looking through a bifocal |
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Common causes:
1) The glasses were not made to the Rx. This could be the result of a lab error, poor handwriting, a transcription error, or a transposition error. 2) The refraction needs to be re-checked. This could be a technical error, or it could be from unreliable patient responses. 3) There is a vertex distance problem. 4) The glasses do not fit well or are dirty. 5) Progressive lenses (see the section on PALs)
Less common causes:
1) A diabetic may be having blood sugar level changes. 2) A contact lens wearer may have some corneal edema after contact lens wear that blurs the vision with glasses. 3) The patient may not have realistic expectations. This usually applies to the patient who does not refract to 20/20, for whatever reason. The doctor may have to discuss with the patient why his vision is not better. 4) The patient has had a decrease in vision since the refraction was done and needs to see the doctor for further evaluation.
Progressive lenses, any complaint
Check the following with progressive lenses:
1) Read the glasses to confirm that the correct power is in the lenses. Be sure to read the distance correction near the top of the lenses and the add near the bottom nasal edge of the lens. Make sure the add power has not been cut off in frames with small lenses.
2) Check the base curve and ocular curve if there is a comparison to an old pair of glasses.
3) Find the etching marks. Mark a dot on the symbols with a sharpie and make sure that the patient's pupils are aligned a few millimeters above the center of an imaginary line drawn between the symbols, when the patient is looking in the distance. See Module 17, Section 3 for marking the optical center of a progressive lens.
Be sure that the line drawn between the two etching marks is horizontal when the glasses lay on a flat surface. If it is not horizontal, then the the add power will be rotated out of alignment. Sometimes, simply turning the lens in the frame will solve the problem, if the axis is not adversely affected.
Of course, a significant discrepancy in either of the above two points, that cannot be solved by a frame adjustment, would warrant a re-make.
4) Be sure the frames fit with a short vertex distance. In other words, observe the fit of the frames and make sure that the glasses fit close to the patient's eyes. Because the viewing corridor in progressives is narrow, the closer the lens is to the eye, the wider the field of view will be.
5) Check the patient's vision with the glasses on and observe the patient's behavior. Make sure that the patient understands that the best vision is through a center corridor in the lenses, and that the head must be adjusted up and down to find the area of best vision. The patient may simply need further instruction/practice in wearing progressive lenses.
Even if the above points are OK, any patient with a good pair of progressive lenses may still have one or more of the following complaints:
1) Can only see well through the center of the lenses. 2) Has to turn head to see clearly. 3) Complains of distortion when looking left and right. 4) Reading add seems too low. 5) Reading not strong enough. 6) Sees 20/20 but complains of vision not being sharp.
The patient overly sensitive to the peculiarities of a progressive design may have to be changed to a flat top bifocal or trifocal. Re-check the refraction before advising a lens design change.
What about the patient with no Rx change who gets a second pair of progressives and is more comfortable with the first pair? You can find nothing wrong with the way the new lenses were made and fit. This is a tough one, and it does happen sometimes. Your only hope is to discover that the new glasses were made from lenses from a different manufacturer. If so, advise that the glasses be re-made with the original lens type.
A person with a 20/20 refraction should be able to read J1 (20/20) print at 16 inches away. We know from the formula D = 1 / f(m), that this patient may need less than a +2.50 add (depending upon age), but he will not need more than a +2.50 add for this distance. This is your standard to go by.
If this 20/20 person can't see J1 at 16 inches, then there is either something wrong with the basic refraction, the way the lenses were ground, the alignment of the bifocal, or the focal distance (were the patient holds the reading material).
Sometimes a patient is inadvertently given a weaker add power as compared to the old glasses because the distance correction was changed, but the add was not correspondingly adjusted. Example:
Old glasses: -1.00 Sph, +2.25 add, no reading complaints New glasses: -1.50 Sph, +2.25 add
The total reading power in the old bifocal is +1.25. The total reading power in the new bifocal is +0.75. To keep the same focal distance, the patient will need a +2.75 add in the new glasses.
A person with less than 20/20 vision should have equivalent near vision at 14-16 inches. For instance, a person with 20/80 BCV at distance should be able to see about J7 at 14 inches with the appropriate add for his age. These patients are typically given stronger adds to reduce the focal distance and make the print appear larger. For example, a 70 year old with 20/50 BCV may be given a +3.50 add to focus at 11 inches and would perhaps be able to read J2 print at this distance.
The point is that you need to make sure that the add is appropriate for the patient's visual acuity and that the patient understands what focal distance (reading distance) is optimum for the particular add. Low vision patients sometimes need help (in an understanding way) to align their expectations with their visual acuity. A referral to a low vision specialist may be helpful.
This is one of the most frequent glasses complaints. The obvious problem is that there is too much plus power at near, bringing the focal distance too close. If there is a problem with the distance vision also, you will need to re-refract. If the distance vision is good, hold up a pair of -.50 trial lenses over the bifocals to see if that moves the focal distance out far enough. If not, go to a -.75 or -1.00 over-refraction at near.
A common cause of this problem is increasing the distance plus correction and the add power at the same time. For example, a +1.00 hyperope with a +1.50 add is complaining of reading difficulty. The distance is changed to +1.50 and the add is changed to +2.00, when the patient would do nicely with only the +1.50 distance adjustment which changes the reading power from +2.50 to +3.00.
Cannot see the computer screen well, or has to tip head back to see the computer screen
Most people view a computer screen straight ahead or slightly lower, not in the reading area of the lens. A bifocal is not the optimum lens for computer viewing because of this, and the fact that bifocals are not made for viewing objects at arms length. Trifocals and progressives are better because they are designed for use at intermediate viewing distances, but the patient may still have to tilt her head back to see the screen well.
The optimum solution for the presbyope is a pair of bifocals, or progressives, with intermediate strength in the distance part of the lens, and reading power in the lower portion of the lens. The Clinical Optics Calculator has a calculator for this situation that will give the Rx for any distance. Another popular solution is single vision lenses with the intermediate vision prescription. Give the patient the options and let him decide which would be best, because cost is always a factor. Of course, the time to figure this out is before glasses are ordered, not after.
Can only read with one eye, or closes one eye to read
This may be an older person with a muscle balance problem (convergence insufficiency?) at near who may have noticed the problem after new glasses were made, or perhaps the new prescription aggravates the problem. The patient may be closing one eye to relieve double vision or eye fatigue at near. Pay close attention to the alignment of the bifocal segs. Have the segs been decentered enough to line up with the patient's near PD? Assuming a systematic check of the new glasses checks out OK, an evaluation of a possible eye alignment problem may be needed.
If anisometropia is involved, see double vision or discomfort only when looking through a bifocal below.
Another possibility is the macular degeneration patient who has poor central vision in one eye. However, for this patient it is usually not a new complaint. Most of these patients simply ignore the "black spot" in the poor eye, although some do have to close the eye or patch it when reading.
The eyes don't focus at the same distance at near
Accommodation is a binocular function, meaning both eyes accommodate the same amount unless there is a physical abnormality. The add power should be the same in each eye unless there is a condition such as a young person with an IOL in one eye only. This complaint makes you think that the distance correction is not balanced. Re-refract and balance the refraction.
More often than not, this complaint comes from a low hyperope (e.g., +1.00 to +2.00 distance correction). These patients are used to accommodating, and if you relax the accommodation too much by pushing plus in the correction, you sometimes get this complaint. The only solution is to back off a little on the correction. Perhaps change a +1.50 Sph to a +1.00 sph.
Since most hyperopes benefit from pushing plus, don't let these complaints modify your technique unless you are getting them often. A good way to avoid this complaint is to balance the correction. If you use balancing, you will hardly ever get a myope complaining of being over-minused.
Sometimes a patient who has changed lens materials will have this complaint. Perhaps going from regular plastic lenses to high index lenses. The patient should be encouraged to try to get used to the change. If that doesn't work, you may have to go back to the old material.
Distortion, including slanting lines
This can be caused by induced prism, a base curve change, a major change in the prescription (particularly cylinder power and axis), a change in lens thickness, or a change in lens material.
By far, the most common causes of this complaint are a base curve change or a major prescription change. A significant base curve change will be detected in your initial evaluation of the glasses. As discussed in Module 17, Section 2, it is a change in the ocular curve that causes the problem.
Common prescription changes that cause distortion are a change in a plus lens correction of more than .75 D, a change in cylinder power of more than one diopter, or a change in cylinder axis of more than 15 degrees in a cylinder with more than one diopter of power. Does this mean that you should never make changes above these amounts? Of course you can, but be sure that there is a significant improvement in vision. Most of the time the patient can get used to the way the world looks through the new glasses if you can demonstrate a significant benefit in better vision.
What about the patient who has had a huge change in cylinder power? Perhaps he is post-op and he changed from a one diopter cylinder to a three diopter cylinder. Re-refract this patient and try to reduce the cylinder amount by giving the patient a choice between spherically equivalent lenses. If the Rx is -1.00+3.00x30, have the patient look at a line that is easily read, and show her the difference between that lens and -0.75+2.50x30. The technique requires some dexterity on your part, as you have to change the sphere wheel one click and the cylinder wheel two clicks at the same time. Sometimes there is no change in the vision, or very little change, as your reduce the cylinder power this way. Continue reducing the cylinder power in this manor until there is a significant reduction in vision.
What if the patient needs all that cyl power for good vision? The only thing you can suggest is that the patient try to keep looking through the optical centers of the lenses and turn her head to view to the side, and tilt the head to view up and down.
Don't forget that lens thickness is dependent on lens size as well as lens power. If the glasses lenses are large, you might suggest frames that hold smaller lenses. This will reduce lens thickness and distortion.
Be on the look out for the patient who has switched to high index lenses. The view may seem distorted as compared to the old glasses. Advise that adjustment period will be needed, without switching back and forth between old and new glasses.
Headache, eye soreness, eyestrain
As with distortion, these symptoms can be caused by induced prism, a base curve change, a major change in the prescription (particularly cylinder power and axis), a change in lens thickness, or a change in lens material.
The first suspects you should think of are a base curve change or induced prism, so check these carefully. If there is no obvious cause, you will need to re-refract. Sometimes you will not be able to detect anything wrong with the glasses for a patient with these complaints. If so, you will need to demonstrate to the patient that you have thoroughly checked all the possibilities.
There is one situation that is unusual, but it does turn up on occasion. This is the patient with a new pair of glasses that has the PD matching the OCD perfectly, but the PD and OCD do not match in the old glasses. In other words, the patient has gotten used to some (unintended?) induced prism in the old glasses, and when it is "taken out" in the new glasses, the patient has symptoms of discomfort. When evaluating this patient, be sure to check the muscle balance. You may find that the induced prism matches up well with a phoria (or intermittent tropia). For example, suppose the induced prism is base-in OU. Upon checking the motility, you find that the patient has an exophoria. No wonder the patient likes the old glasses! The answer to this problem is to re-do the prescription with an equivalent amount of prism correction.
You may be thinking that this patient had a prism correction prescribed in the old glasses, and it was just missed in reading the glasses. This does happen, of course, but the patient with a prism correction usually complains of double vision if the prism is missing. It is easy to check if you have access to the old prescription. Sometimes the patient knows that there was a prism correction, or perhaps he relates that there was "something special done to the glasses".
Double vision when looking straight ahead
This is about the patient who complains about double vision with the new glasses and has no double vision with the old glasses.
The first thing to investigate is the possibility of a prism correction in the old glasses that was missed, or perhaps the prism correction was not written on the prescription. Some patients are not aware that they have a prism correction in the glasses, and if it is a low amount, it can be missed when reading the glasses. However, you might think think that a clue would have been found in the muscle balance evaluation (see Module 5).
How would you avoid an error like this? When reading the glasses with the lensometer, pay attention to where the optical center should be. When reading a single vision lens, the optical center should be somewhere near the geometric center of the lens, perhaps a little bit nasal to the center of the horizontal midline. When reading a flat top bifocal, the optical center should be just above the bifocal line, in the middle. If the mires of the lensometer do not line up close to the center when aligned with these areas, suspect a prism correction.
When reading prism with a lensometer (manual or auto), remember that you will not have an accurate reading of the horizontal prism amount in each lens without knowing what the patient's PD is. The PD must be marked on the lenses and the lenses must be read at those marks. The PD does not have to be know to measure vertical prism, but the frame must be against the lens stage and the lens stage must not be moved when reading each lens.
If there was no intended prism correction in the picture, check the optical centers for induced prism (Module 17, Section 3). If the patient is post-op, suspect a possible muscle balance complication from the surgery.
Anisekonia can also cause double vision with glasses. Anisekonia is a condition in which the image on the retina of the right eye is a different size than the image on the retina of the left eye. The brain has difficulty fusing the images because of the size difference. This can be caused by some retinal disease processes, but is usually due to anisometropia.
Anisometropia is a significant difference in the refractive error between the two eyes. An extreme example would be aphakia in one eye (+12.00) and nearsightedness in the other (-3.00).
The effects of lower degrees of anisometropia are made worse by antimetropia, which is a plus lens correction in one eye and a minus lens correction in the other eye.
Anisometropia is not uncommon when a patient has cataract surgery in one eye only. The correction may be +3.00 OU before surgery and +3.00 OD, -0.50 OS after surgery. Most patients can accept this situation on a temporary basis, perhaps by only using drugstore readers. If this will be the situation for a prolonged period of time, a contact lens in the right eye may be indicated.
Double vision when looking through a lens edge
An example of this would be the patient who complains of double vision only when looking to the right with the new glasses. Typically, these patients have had a significant power change in the glasses, perhaps a lens edge is thicker than it was in the old glasses. If the muscle balance, glasses readings, and refraction check out to be what they should be, your only solution will be to suggest that they patient not look through the extreme edge of the lens and turn her head to view closer to the center of the lenses.
Double vision or discomfort only when looking through a bifocal
This complaint may be caused by anisometropia. The resultant glasses prescription usually has one lens with a plus edge (thin) in the reading area while the fellow lens has a minus (thick) edge in the reading area. When looking through the bifocal, there is sufficient induced prism to cause double vision or discomfort. The solution is to either prescribe a slab-off, or two pair of glasses, one for distance, and one for reading. For a detailed discussion of slab-off grinding, see Module 18, Section 2.
You may be wondering why a slab-off was not prescribed in the first place. Despite the fact that the rule-of-thumb is to prescribe a slab-off if the induced prism at 90 is greater than 1.5 D, it is very difficult to predict which patient will need a slab-off based solely on the amount of induced prism. It is surprising how many patients with induced prism at 90 greater than 1.5 D do well without a slab-off. For this reason, some doctors will not prescribe a slab-off unless the patient returns with a complaint.
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