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Point spread function provides more accurate refraction, speaker says
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SEATTLE – Refracting patients with a device that uses point spread function instead of Snellen letters provides more sensitive results without the need for binocular balancing, a clinician said here at Optometry’s Meeting.
David I. Geffen, OD, FAAO, performed a study in the right eyes of 30 patients who presented for a routine exam in his practice. He presented his results in a poster here at the meeting and also in a “live poster session.”
According to the study abstract, each patient first underwent a subjective refraction with a standard phoropter with binocular refraction using +1.0 D fogging in the fellow eye and binocular balancing in the end. Then a monocular refraction was performed with the PSF Refractor (VMax Vision) in the same eye, without binocular balancing.
“In our study, we found that the consistency of the PSF with normal phoropter refracting was 97%,” Geffen told the audience. “Only 3% of patients found a difference greater than 0.25 D.”
Geffen said he comanages LASIK patients, where the objective is optimizing vision.
David Geffen
“Point spread function (PSF) refraction is more sensitive,” he said. “Changes of 0.05 D are now noticeable. We all know the #1 higher-order aberration is spherical, and #2 is coma. Patients who are 20/20 say they can’t see well at night with contact lenses. If you don’t address their problem, they will go somewhere else.”
The VMax system will help you prescribe contact lenses more accurately, and digitized spectacle lenses can be made more precisely, Geffen said.
“Its level of accuracy is much higher, and it’s more sensitive,” he said. “It’s five times more accurate than a phoropter, and patients feel like you’ve come into the 21st century.
“How have we gone 100 years without improving upon the test we use every day on all patients?” Geffen asked. “Refracting is hard on us,” he said, with many optometrists having back problems and carpal tunnel syndrome.
The VMax system is also less straining on the patients, he added.
“The older patients love my point spread refractions the most,” Geffen said. “It’s much easier to tell the difference in a point spread. You can increase or decrease the size of point spread, you can take an age-related macular degeneration patient and you can increase the target and get them the best refraction possible. You can decrease the contrast of the target and do contrast testing. It’s very good for pathological conditions.”
Geffen said the VMax system prevents overminusing because the target will look blurry again.
“Once you have experience using PSF, you will find it saves you 50% to 60% of the time with a phoropter,” he said, “and you do not have to binocular balance in your office. The target will look blurry if I give them 0.25 D more minus. I feel comfortable not binocular balancing; my re-do rate is much lower. I’ve had the unit for 4 years, and we’ve done thousands of eyes.”
Geffen said the current unit adds an autorefractor. “It’s basically a lane in a box,” he said. “If you have a space problem in your practice, this could be the solution.” – by Nancy Hemphill, ELS, FAAO
Disclosure: Geffen is a consultant for VMax Vision.