By Henry Greene, OD, FAAO
Over the years experienced practitioners tend to ‘go where the action is.’ What this means to me is that we refine our testing methods to do the tests that are most instructive in managing the patient and stop doing tests that don’t tell us much.
One such test that I have found very helpful is testing for ocular dominance. I’ve written a short blog post about Ocular Dominance and I’ve shared it here.
All of us have a dominant eye, just as we do a dominant hand and foot. Some of us have a very strong dominance while others can easily switch between eyes. I have a very strongly dominant right eye. I can barely localize when looking through a monocular telescope with my left eye, and it took forever for me to learn to use my left eye with my handheld ophthalmoscope (dating myself, aren’t I?)
As we know, the dominant eye superimposes over the non-dominant eye. If the non-dominant eye is the only eye with reduced acuity, the patient might not even notice it. However, if the dominant eye has the reduced acuity, they’ll be on the phone to us immediately.
Whenever I have a patient with markedly different acuity between the eyes, I always have them cover the poorer-seeing eye. If they report that they see better with that eye closed, than the covered eye is likely the dominant eye and this will impact all my prescribing decisions both distance and near. When the poorer-seeing eye is the dominant eye and it drags down binocular vision I call it a “dominancy conflict.”
Most individuals find that sighting and localizing through a monocular telescope is much easier when using the dominant eye. In fact, many individuals are unable to aim or sight through a telescope with the non-dominant eye (like me!). As a result, the ability for the patient to localize through a bioptic telescope will be much more natural if they are using their dominant eye.
Another easy way to determine the dominant eye is to ask the patient to look through a monocular handheld telescope without suggesting which eye to use. (I use a handheld 2.2x Galilean for BCVA of 20/100 and better, or a 4×12 Keplerian pre-focused for the chart distance for 20/125 and less.) They will usually bring it to their dominant reflexively. And, since I already know which is the better seeing eye, I’m keeping my fingers crossed (behind my back) that they bring it to the better-seeing and hence dominant eye!
If they ask which eye they should use, I suggest they bring it to whichever eye seems more natural. On occasion, patients will show no ocular preference and can sight equally well with either eye, for which I send up a prayer of thanks, however this is less common.
When thinking about bioptic telescopes, if I have a dominancy conflict I will try to prescribe a binocular system in lower powers or if I need a monocular device, I would often prefer to prescribe a higher power to the dominant eye so long as I can get the acuity through telescope that I seek. If I have to prescribe to the non-dominant eye, I might consider a sector occluder so when the patient dips their head to sight through the bioptic the fellow eye is covered. However, even with occluders and/or lots of training I have usually found that these folks have a bit more of a challenge thriving with their bioptic and I will warn them about that right away.
Hope this little tidbit helps you as much as it has helped me.