Can we make binocular balancing a thing of the past?

By David Geffen, OD, La Jolla, Calif.

In optometry school, we are well trained in optics and the art of using the phoropter to subjectively refract our patients. Part of this training includes learning to perform binocular balancing. While this is something that must be done in the majority of patients, we have been able to almost eliminate it as the result of adopting a new technology that uses point-spread-function to obtain a subjective refraction and increased visual acuity.

Why it’s needed

Binocular balancing is the step in subjective refractions that involves matching the accommodative stimulus for the two eyes. It also has a secondary purpose in that it relaxes the accommodation as a result of both eyes being open. In addition, binocular balancing enables the matching of the visual acuity between two eyes, particularly in younger patients who can easily accommodate.

Binocular balancing is required because there is a risk of overminusing a patient during a subjective refraction when using a phoropter and Snellen letters. This is because the letters appear to be getting smaller and darker as a patient accommodates – making it difficult for the patient to discern a difference in his or her vision. Plus, depending on the binocular balancing technique that is used, you may not even be able to perform it in a patient if you’re not able to achieve the same corrected visual acuity in both eyes.

However, if you use a device that utilized point-spread-function for the subjective refraction, the point is much more sensitive and will become blurry if too much minus is used. This makes it much easier for the patient to detect a change as you perform the subjective refraction.

When we first started to use a system that employs PSF targets rather than letters (PSF Refractor, Vmax Vision, Maitland, FL), we didn’t immediately realize that we could eliminate the need for binocular balancing. But, it became clear after a clinical study that we participated in comparing the subjective refraction and visual acuity results between the PSF and a standard phoropter – the refraction results are just better and it’s due to the increased accuracy of the results that we obtain with the PSF target. Since this study, I use this device about 90 percent of the time and I’ve never had an issue with overminusing a patient.

Delegating refractions

The other aspect of eliminating the need for binocular balancing by using the PSF Refractor™ is that it makes delegation of the subjective refraction to a technician much easier. For an optometrist, binocular balancing is something that we learn to do as part of our training on the phoropter. It’s a fairly straightforward task and is a necessity when using Snellen letters. Problems arise, however, when the task of subjective refractions is delegated — because techs lack the optics training that optometrists receive, it is one of the hardest steps to learn in the process.

There are many nuisances to becoming a good refractionist with a phoropter – this is not the case with the PSF device and this can lead to efficiencies in patient exams and work flow. In my practice, it takes about three minutes to perform the subjective refraction with the PSF device compared to five minutes with a standard phoropter. In a busy clinic, where you can have 50 patients scheduled in a day – this can save you almost two hours of exam time.

Patient preference

The final point to consider is that binocular balancing can be confusing for the patient and, with some techniques such as the Von Graefe prism dissociation balance technique, it can be quite disturbing. With the PSF device, its simple – if you’ve put in too much minus, the patient simple tells you that the point is blurry and then you back off. That, as the British like to say, makes refractions “easy peasy” and eliminates the need for the balancing step.

Dr. Geffen practices at the Gordon Weiss Schanzlin Vision Institute where he specializes in family eyecare, contact lenses, low vision and refractive surgery consultations.

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