The case studies are presented in a question-and-answer format. They are composite cases representing situations that will present to the refractionist. The principles discussed apply equally to the plus and minus cylinder methods.
Myopia Case 1
A 24-year-old male myope, despite seeing reasonably well at distance without correction, is “soaking up” minus spherical power during subjective refraction. Why is this happening, and what can be done to determine if it is needed?
Answer
It is important, when performing subjective refraction, to be concerned about giving the patient too much minus spherical correction. Over-minusing occurs as a result of the patient accommodating during the refraction. This is especially a concern with a younger patient because a young person has a great deal of accommodative ability. There is a tendency for the extra minus power to be preferred by the patient because the letters on the acuity chart will look smaller and darker and, thus, “better.”
There are several techniques that can be employed to try to prevent over-minusing during subjective refraction:
▸ The patient should be instructed, and reminded, to compare only the clarity of the choices being shown. It should be emphasized that if a given choice only makes the letters smaller and darker, it should be considered “the same.”
▸ The refractionist should make certain the additional minus is resulting in improved ability to read the acuity chart.
▸ Fogging techniques can be employed so that the patient is moving from a position of extra plus. (See Over-Minusing on page 60.)
▸ The red-green duochrome test can be used. (See Over-Minusing on page 60.)
▸ A cycloplegic refraction can be performed. (See The Three Types of Refraction on page 32.)
Myopia Case 2
A 75-year-old female is found to have a -1.00 diopter change in refractive error in each eye from the prescription of 1 year ago. What are the possible etiologies of this myopic shift? What are the considerations before giving her a prescription for a new pair of glasses incorporating this myopic shift?
Answer
Possible etiologies include a nuclear sclerotic cataract, the onset or worsening of control of diabetes mellitus, a recent scleral buckle, some medications (e.g., tetracycline, topiramate), and hyperbaric oxygen treatment.
If it is determined that the myopic shift is due to a cataract, it should be explained to her that the change in prescription will offset, but not overcome, the cataract (unless it is very mild).
The change in prescription measured should be shown to her binocularly at distance and near. A decision will have to be made, with the patient, whether the change will allow satisfactory performance of activities of daily living.
If, after discussion, it is unclear whether the vision will or will not be satisfactory with the new prescription, it is sometimes best to make the change. That way, both you and the patient will know that if there is continued difficulty while wearing the new prescription, cataract surgery is indeed indicated.
If it is determined the myopic shift has resulted from diabetes, it is usually best to remeasure once the glucose level is stabilized.
If a systemic medication is considered to be the etiology of the myopic shift, a decision about changing the glasses will depend upon the length of time the patient is expected to be on the medication. Discussion with the prescribing doctor is at times very helpful.
Myopia Case 3
A 48-year-old male myope, without separate reading glasses or a bifocal, is having no trouble reading. Why? (He is certainly at the age one would expect him to have symptomatic presbyopia.)
Answer
If he is wearing glasses for myopia, almost certainly his myopic refractive error is not fully corrected. He can read at near because of the myopia that remains uncorrected.
In this situation, if the patient feels he is seeing satisfactorily at distance and near, it is often best to not give the additional minus to fully correct the distance refractive error. Keeping him “under-minused” allows him to defer moving to a bifocal or progressive addition lens (PAL) for a little while. If he were to be given the full myopic prescription, almost certainly a bifocal or PAL would be needed.
If he is not functioning satisfactorily at distance, then the full myopic prescription can be given, with the addition of a bifocal or PAL. The decision about when to no longer use a single-vision lens is best made with the patient.
Note
An extension of this concept can be seen in individuals with myopia who take off their glasses to read. They are reading with what can be termed their “natural nearsightedness.”
Myopia Case 4
A 37-year-old female myope seeing well at distance with her glasses is having trouble reading. Is this presbyopia?
Answer
For someone 37 years of age, presbyopia is not the most likely diagnosis. It is much more likely she is over-minused at distance. Her trouble reading is, most probably, the result of having to use her accommodative ability to offset the excessive minus in her glasses. She, therefore, does not have enough accommodation left to use for reading.
Note
Let the patient know that the new glasses you will be prescribing, with less minus sphere, may require a little adjustment period for seeing clearly at distance, as accommodative tone may take a little time to relax.
Myopia Case 5
A 55-year-old male with high myopia presents for routine examination. You determine that he does not need a change in glasses and that his eyes are in excellent health. When discussing those results, what else should you tell him?
Answer
Because an individual with high myopia has an increased risk of a retinal tear and subsequent detachment, it is important to instruct him to call immediately should he have the onset of new floaters, flashes, or a change in side vision. This reminder should be repeated and reinforced when you see him in the future.
Myopia Case 6
A 30-year-old female who has never worn glasses is examined and found to have a small amount of myopia. She says she does not feel she needs distance glasses. Should you prescribe them?
Answer
If she feels she is seeing satisfactorily at distance and you have found only a small myopic correction, it is fine for her to continue to function without distance glasses.
Were you to prescribe the glasses for her, the proper instructions would be that they do not need to be worn all the time—only when she wanted their help. She has indicated it is unlikely she would use them, so it would probably be an unnecessary expense.
Myopia Case 7
A 35-year-old male wearing glasses for myopia is examined, and you measure a very slight increase in his myopic correction. Should you make it?
Answer
The best way to determine if this change should be made is to show it to him and let him decide whether he feels it is a significant enough improvement to warrant the purchase of a new pair of glasses.
Note
This is a good rule-of-thumb to follow for any anticipated change in prescription.
Hyperopia Case 1
A 37-year-old male with a new, single-vision, hyperopic correction in his glasses is seeing well at distance, but is having difficulty reading. Is this presbyopia?
Answer
He most likely has hyperopia that is not being fully corrected by his glasses. He is, therefore, using his accommodative ability to correct the latent hyperopia, leaving an insufficient amount of accommodation for reading.
When measuring to uncover latent hyperopia, one may perform a cycloplegic refraction or “push plus.” The latter is accomplished during a noncycloplegic refraction by giving as much plus spherical power as the patient will tolerate without causing blurring or discomfort. (See Hyperopia Case 3 on page 82.)
Note
Latent hyperopia can (not uncommonly) be present in individuals who see well at distance without glasses and are not known to be hyperopic.
Hyperopia Case 2
A 50-year-old female who has never needed distance glasses and is successfully using over-the-counter (OTC) reading glasses is now beginning to have trouble with distance vision. Why, and what might you recommend?
Answer
Her difficulty at distance is almost certainly due to latent hyperopia that has now become manifest. Prior to age 50 years, she was able to use her accommodative ability to correct her distance vision, but now there is not enough accommodation left to do so.
If she does not want a bifocal or PAL and does not mind having two pairs of glasses, there is an inexpensive way to correct her vision for distance and near. If she has a low and symmetrical amount of hyperopia, with no astigmatism, she can use OTC reading glasses for distance. For example, she may do well using a +1.00 pair for distance and a +3.00 pair for near.
Hyperopia Case 3
A 25-year-old male found to have latent hyperopia was recently given a glasses prescription following a cycloplegic refraction. He is now complaining that he cannot tolerate the new glasses. What should be done?
Answer
He should return for a post-cycloplegic refraction.
If a significant amount of plus sphere, not previously worn, is found on a cycloplegic refraction, it is best to bring the patient back for a post-cycloplegic refraction before writing the final prescription. The purpose is to determine how much of the full cycloplegic refraction can be tolerated.
A lesser amount than the full hyperopic correction may need to be prescribed initially because the long-standing accommodative tone, which has been used to self-correct the latent hyperopia, can be resistant to relaxation. Over time, this tone will decrease and, subsequently, additional plus can be added in stages until the full hyperopic correction is accepted. (See Hyperopia Case 1 on page 81.)
Hyperopia Case 4
A 64-year-old female returns for her annual visit and is found to have developed a hyperopic shift in her prescription. What are two possible etiologies?
Answer
- Macular edema
- Recent initiation of treatment, or treatment change, for diabetes mellitus that had previously caused a myopic shift (now reversed).
Hyperopia Case 5
A 6-year-old female is examined and found to have a refractive error of +1.25 in each eye. Should glasses be given?
Answer
Because of her young age, and if strabismus is not a factor, glasses should not be given for this refractive error. She has ample accommodation to correct the hyperopia, and it will be invoked without any conscious effort.
Note
It is also not necessary to give a correction for a small amount of astigmatism at this age.
Astigmatism Case 1
A 35-year-old male patient calls, having just begun wearing the new glasses you prescribed.
| His previous prescription: | OD -2.25 + 1.00 × 90° OS -2.00 + 1.00 × 90° |
| The prescription you gave: | OD -2.50 + 1.75 × 75° OS -1.75 + 1.50 × 105° |
He says that, with the new glasses, the top of his desk looks slanted and, when walking, he has some nausea and the floor seems to be rising.
What is the most likely cause of his symptoms?
Answer
The symptoms are almost certainly due to the change made in the astigmatism correction in the new prescription.
The astigmatic portion of a glasses prescription is the most prone to cause difficulty. A change in cylinder axis, especially with higher cylinder powers, is always a concern. A “trial run” prior to prescribing may very well have avoided his problems. (See Trial Run on page 68.)
Astigmatism Case 2
A 26-year-old female who has never worn glasses presents complaining of decreased distance vision. If retinoscopy is not performed, and an autorefractor is not available, how do you determine if cylinder is present?
Answer
(See Sixteen Tips for Accurate Subjective Refraction Results, Tip 9 on page 64.)
Astigmatism Case 3
A 34-year-old female, at the phoropter, is beginning subjective refraction with the following prescription in one of her eyes: -3.50 + 0.50 × 180°.
The spherical correction in Step 1 is determined to be -3.00, and in Step 2, the axis remains unchanged. (See The Four Steps of Subjective Refraction on page 33.)
You begin modifying the cylinder power of +0.50 × 180 with the Jackson cross cylinder, and she says the choice with the red dot is clearer. Therefore, you lessen the cylinder power to +0.25 × 180°.
On the next series, she again chooses the red dot and you lessen the cylinder power to 0.00 × 180°, and add +0.25 power to the sphere.
On the next sequence of choices she once again chooses the red dot, but you are working with plus cylinders and cannot go any lower. What can you do?
Answer
The patient is choosing less plus cylinder power when the cylinder power is already at 0 and therefore cannot go any lower. This dilemma is resolved by understanding that the patient is actually choosing plus cylinder power 90 degrees away. In this case, change the axis from 180 degrees to 90 degrees, dial in +0.50 diopter of cylinder power at 90 degrees, adjust the sphere by 0.25 diopter, and then begin again to refine cylinder axis and power. (See The Rule below.)
Note
The Rule: If a patient chooses “less than 0” cylinder power, the axis should be shifted 90 degrees from its current location. This applies to both the plus and minus cylinder methods. (See Sixteen Tips for Accurate Subjective Refraction Results, Tip 9 on page 64.)
Astigmatism Case 4
A 25-year-old female myope, who previously had a small amount of astigmatism, is choosing a large amount of plus cylinder power during subjective refraction. Why?
Answer
It may be that there has simply been an increase in the astigmatism, or a corneal problem such as keratoconus could be the cause. However, it is important to make sure this is not the result of over-minusing the sphere, which will necessitate an increase in cylinder power.
For every 0.50 diopter a patient with plus cylinder is over-minused, the cylinder power needs to be increased by 1 diopter to maintain the spherical equivalent and keep the circle of least confusion on the retina. (See Spherical Equivalent of an Astigmatic Prescription on page 23.)
For example, if a patient has a true refractive error of -3.50 +0.50 × 180°, the spherical equivalent of the correct prescription is -3.25.
If the sphere is over-minused by -0.50 diopter (to -4.00), the patient will choose an increase in cylinder power of +1.00 diopter (to +1.50), with a resulting spherical equivalent of -3.25.
The increased cylinder power will be preferred because letters will appear most clear at the spherical equivalent.
This results in a measured correction of -4.00 +1.50 × 180°.
In summary, over-minusing the sphere results in an incorrect measurement of cylinder power.
Note
Conversely, if sphere is over-minused in the minus cylinder method, the patient will choose less than the true cylinder power. (See Over-Minusing on page 60.)
Astigmatism Case 5
A 45-year-old, newly presbyopic male is examined and found to have, in each eye, a distance refractive correction of plano +0.50 × 90° and a near correction of +1.50 +0.50 × 90°. He has never had distance glasses and his only difficulty is with reading. What should you give?
Answer
If he feels he is seeing fine at distance and would simply like help with reading, he may do quite well with OTC reading glasses. A strength of +1.75 would be recommended based on the spherical equivalent of the near measurement. It is not necessary to give a prescription incorporating the astigmatism correction unless his reading or distance acuity is significantly improved with the addition of the cylinder, and he wants it.
Astigmatism Case 6
A 14-year-old female, who has not had a previous refraction, complains of trouble seeing at distance. Subjective refraction results in the following prescription:
| OD -1.75 + 0.50 × 100° | VA 20/20 |
| OS -1.50 sphere | VA 20/25 (pinhole 20/20) |
No organic etiology is found to explain the lesser acuity in the left eye.
What should be the next step?
Answer
Because the astigmatic correction for a patient is often symmetrical, a helpful next step would be to look for that possibility. Complete symmetry would indicate a refractive error for the left eye of -1.75 + 0.50 × 80°. When symmetrical, the axes add to 180 degrees. Repeat subjective refraction for the left eye could begin with that prescription, and note that the correction originally found is the spherical equivalent of the new starting point.
Presbyopia Case 1
A 45-year-old female presents with the complaint when trying to read, “My arms aren’t long enough.”
What is the diagnosis and what should you prescribe?
Answer
Her symptom is the result of presbyopia.
The patient’s age is 45 years. This is usually when the initial correction of presbyopia is necessary, not age 40 years as is often stated. If presbyopic symptoms occur before age 45 years, make certain the patient is not over-minused or a latent hyperope. These may be the cause of the earlier-than-usual onset of presbyopic symptoms. Conversely, if a patient is reading satisfactorily without correction in the late 40s, it is very likely some uncorrected myopia is present.
The treatment for presbyopia would seem to be very simple, but surprisingly there are four categories of solutions, and additional choices within the categories.
The four categories are as follows:
1. Give nothing: If she has mild-to-moderate myopia and has been taking her distance glasses off for reading, it is fine to have her continue to do so. When the glasses are off, she is reading with her “natural nearsightedness.”
2. Give reading glasses: She can be given a prescription for reading glasses or, if appropriate, instructed to purchase OTC reading glasses.
Three things to consider with regard to OTC reading glasses:
a. OTC reading glasses are sometimes referred to as drugstore reading glasses, readers, cheaters, or magnifiers. Although OTC reading glasses are called magnifiers, their purpose is not magnification. Their function is to supplement the patient’s diminished focusing ability. That focusing ability, before it was lost, focused the print but did not enlarge it.
The proper strength for OTC reading glasses is determined by finding the amount of plus power that best focuses the reading material without magnifying it. The reason to refrain from giving additional plus power, which would produce magnification, is that it would result in an unnecessarily closer and narrower reading range. An exception to this is for a patient with low vision where magnification is purposefully given.
b. OTC reading glasses are appropriate when three criteria are met:
♦ The patient must be essentially emmetropic at distance. (If glasses are worn to correct a distance refractive error, an Add is typically prescribed.)
♦ The two eyes must be reasonably symmetrical in their refractive status. OTC reading glasses have the same strength lens for each eye.
♦ The patient must have no astigmatism, or an insignificant amount. OTC reading glasses have spherical plus power only.
Note
When these three criteria are met, OTC reading glasses can be recommended with confidence. The strength designation found on the glasses can be relied upon, the quality of the lenses is good, and there is a significant cost saving for the patient.
c. Three types of OTC reading glasses are made, and it is helpful to discuss with the patient the pros and cons of each type to determine which is likely to work best:
♦ Half-glasses:
Pro: Allows for distance viewing over the top of the glasses.
Con: Some individuals prefer to not have this style.
♦ Full reading glasses:
Pro: Gives the patient a larger reading area than the half-glasses.
Con: The glasses need to be removed for distance viewing.
♦ Plano bifocals (plano at top; flat-top bifocal at bottom):
Pro: Allows the patient to alternate between distance and near.
Con: Some patients prefer to not have bifocals.
Note
It is helpful to write down for the patient the strength and type of reading glasses decided upon. When doing so, it is best to write “OTC” clearly on the prescription to avoid confusion if it is taken to an optical shop.
3. Give two pairs of glasses, one for distance and one for near: This choice may be especially appropriate if distance glasses are used only for certain tasks, such as driving. The patient may then prefer to have separate distance and reading glasses, using each pair when appropriate.
This choice is probably not best if someone, at work or home, has a need to frequently alternate vision from distance to near and vice versa. This would necessitate an inconvenient amount of switching between the two pairs.
Two pairs of glasses may also be preferred by a patient who is overly concerned about using a bifocal. A new presbyope may sometimes choose to begin with separate reading glasses for this reason, knowing a change to a bifocal or PAL can be made if switching back and forth between the two pairs of glasses is occurring too often.
4. Give bifocal or multifocal glasses: This choice works best for most people as it is the simplest and most efficient way for the presbyope to have best corrected vision both at distance and near. In daily life, we are constantly alternating our gaze from far to near, as well as in-between. Teachers are a prime example because they often have to read and look out at a classroom of students in the same setting. Also, some individuals like to sit and simultaneously read or knit while watching TV.
It is good to be aware that, for some patients, the initial prescription of a bifocal is a cause for worry or even mild distress. Some are concerned about adjusting to them, while others consider it an unpleasant indication that they are getting older. If these concerns are detected, gentle reassurance can be quite helpful.
It is important to discuss with the patient that there are three primary ways a presbyopic Add can be given. It can be given as a standard bifocal, a trifocal, or a PAL, the latter sometimes referred to as a no-line bifocal. It is best to discuss the pros and cons of each of these options with the patient to determine which is most appropriate.
The standard bifocal has a line and may be given as a flat-top segment or, less often, as an executive bifocal. In the latter, the bifocal segment occupies the entire lower portion of the lens. The intermediate distance is not corrected by a standard bifocal.
The trifocal has three distinct segments, with two separating lines. The third (middle) lens corrects the intermediate distance. Gaps between distance and intermediate, as well as between intermediate and near, do exist. The trifocal is prescribed with much less frequency now that the PAL is available.
The PAL is a graduated multifocal. Plus power increases progressively from the distance portion at the top of the lens to the full strength Add at the bottom. This lens allows one to focus from distance to near, without any gaps, by looking further down the lens.
Note
It is important to let the patient known that, when a progressive lens is working properly, distance vision should be clear when he or she is looking straight ahead, near vision should be clear when he or she is looking down in the usual reading position, and it is only in the intermediate area where some adjustment with chin-up positioning needs to be made. The closer the object, the higher the chin needs to be. After a short while, positioning for the intermediate distance should happen essentially automatically.
The great advantage of the PAL is that it allows clear vision at all distances, allowing one to function very similarly to how one did prior to the onset of presbyopia!
It needs to be mentioned to the patient that there is an inherent blur at the sides with the PAL. This does necessitate straight-ahead viewing for most things, especially reading. Most patients are able to adjust to this easily as now movement of the head is necessary as one reads across a page rather than moving only one’s eyes. Of note, the free-form progressive lens has greatly improved side vision in the PAL.
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