What I’ve learned from 40 years of refracting low vision patients- or, how to not embarrass yourself.
Henry Greene, OD, FAAO
Three things I always try to remind myself:
- You can’t get big improvements in acuity from small changes in refraction
- Make certain the patient passes the “O” test
- If they can almost see something, they still can’t see it.
What I use–
- The retinoscope- my trusty friend
- Lens flipper (+/- 0.50; +/-1.00)
- Trial frame
- Jackson crossed cylinder (0.50D is all I’ve ever needed)
- Digital chart
- Faces across the room
- Getting out of trouble- what to check when they come back complaining
The Grim reality-
All of our patients are hoping that we’ll give them a new eyeglass prescription that will give them back their vision. They’ve likely tried countless times before they’ve come to us in low vision– each Rx a quarter diopter or 5-degree axis change different, only to be disappointed again that their vision hasn’t returned. And now, it’s our turn. And we have to be the ‘font of wisdom,’ or more likely the ‘bearer of bad news.’ No change in their eyeglasses is going to help.
Refraction–our first option to improve distance vision.
Of course, refraction is our mainstay. If we can make a sufficient improvement in acuity by refraction, (usually a two-line improvement is required for the patient to experience a functional gain), than obviously that would be our first and most convenient option. A brief retinoscopy through the current eyeglasses (if any) can be valuable to see how close to neutral the reflex is as well as its quality. (Only perform retinoscopy briefly. If you spend too much time you’ll bleach the retina which will often delay and undermine your exam.) If the reflex is dull due to media issues, there might be a surgical option. No amount of lens power will impact acuity if there are significant media opacities. If the patient is post cataract surgery with IOLs (with a clear or open posterior capsule), it is unlikely that they will have a significant refractive error. If they do, there is often an astigmatic component.
Generally, by the time a patient gets to a low vision practitioner, if a new refraction would have been of value, it would have already been prescribed. Remember, small changes don’t make big differences! If a patient sees 20/400 a half diopter or 10 degree axis change will be of little value. Changes in refraction will have more potential impact when acuity is 20/70 or better as a modest change might yield 20/50 and that can be helpful. Improving acuity from 20/400 to 20/300 is unlikely to impact the patient’s functional life. So, as a result I will spend more time refining a refraction when acuity is 20/70 or better. I find keratometry can be a very valuable tool. The character of the mires as well as cylinder can often be missed and this data can sometimes make a difference in better-seeing individuals.
I always use a trial frame; I find it more reliable and it allows for a better rapport with the patient. Trial frames are especially important with high cylinders, because it lets the patient maintain their normal posture rather than an unnatural one induced by the phoropter. This can avoid a host of refraction hassles and follow-up issues.
Remember to make a sufficient enough power change for the patient to notice. If they can’t notice a half-diopter change, then try one or even two-diopter changes. There’s no use in making changes smaller than what the patient can reliably respond to- you’ll waste time, everyone will get frustrated and you’ll not make any progress.
Remember also that the high-contrast acuity chart is not the ‘real’ world—and it can be a poor determiner of an Rx change’s functional value. I find it much more helpful for the patient to look at a low contrast target such someone’s face at the furthest distance that they can normally see it. If the patient can notice a difference, then it’s likely to be of functional value. I want them to pass the “O” test—when the patient says “Oh!” I can see them better. That’s a confidence builder. If they don’t notice a difference, even if there is a refraction change, I usually don’t pursue it further. Keep in mind also that acuity will fluctuate as fixation varies. Don’t let a fleeting acuity improvement fool you into thinking it’s the refraction change that’s helping. The prescription change has to be enough to make a “real” difference! Remember that if the patient can “almost see something” they still can’t see it!
When refraction is the best you can achieve and acuity remains inadequate for the patient’s goals, then there’s only one option left to further enhance distance vision- make it bigger! And, of course, we have only two ways to do that—walk up close enough to see it, or, make it closer optically, and someday we’ll have compelling digital options as well.
How I do it
- The first thing I do is put +1.00 over the eye. If they say it makes it blurry, I’ve learned two things—they don’t take plus power, and they’re sensitive to 1D changes
- Then I’ll put -0.50 over the eye. If it’s going to help they’ll say its better without much thinking. If they hem and haw, they don’t take the minus. If they take the -0.50, I’ll go to -1.00, if they hem and haw then, I’m done.
- Then I’ll take a -0.75cyl and hold it at 180, 90, 45 and 135. If they don’t like anyone of them, I’m done. If they do like one, I’ll put it in a trial frame and fine-tune it.
- Lastly, once I think I’m done, I’ll put +0.50 over the eye and want to hear them say that it’s worse. This confirms that I haven’t over minused them.
This takes longer to explain than it does to do it!
What I look for when they come back complaining?
The first thing I do is see if I can add plus power over either eye. Some folks are what I call minus ‘gobblers.’ Adding minus power can make the contrast appear greater and that can be interpreted as better. If there’s a big cylinder change I’ll rarely prescribe the full Rx, and I’ll keep it toward axis 180 or 90 if I can. If they’re more comfortable with their previous Rx, I’ll swallow my pride and go back to that one.
Having fun yet?