spotlight on technology & technique
Higher-Order Autorefraction
Thanks to wavefront technology, high-speed, objective refraction is reaching new levels of accuracy.
By Christopher Kent, Senior Associate Editor

Refracting a patient is among the most basic of assignments for an eyecare professional. However, manual refraction is time-consuming and subjective, and autorefractors, while convenient, have always had limitations.

Marco's 3-D Wave refractive diagnostic workstation uses wavefront technology to perform the "30-Second Refraction."

Now, the 3-D Wave refractive diagnostic workstation (manufactured by Nidek and distributed by Marco) offers a new alternative: One of the instrument's many capabilities is wavefront-based autorefraction. This combines the advan- tages of autorefraction -- speed and convenience -- with a spectacle correction that's more accurate than those generated by previous autorefractors. In fact, eyecare practitioners using this new option (dubbed the "30-Second Refraction" because of its speed) are finding that nearly half of all refracted patients prefer its refractive correction to the result of a manual refraction.

Furthermore, because the 3-D Wave combines multiple technologies (corneal topography, optical path difference and wavefront analysis) in a single workstation, it can provide detailed information about the entire optical system if needed for follow-up.

The Wavefront Advantage

The 3-D Wave uses dynamic spatial skiascopy wavefront aberrometry to measure the entire optical system. Two things help make its refractions extremely accurate:

► Traditional autorefractors and subjective refractions only take sphere and cylinder into account. The 3-D Wave also measures third- and fourth-order (higher-order) aberrations. It uses vector analysis to combine the second-, third- and fourth-order aberration data and calculate the axis and power of the most effective cylindrical correction, thus obtaining a more accurate starting point. Even stated in lower-order terms, the resulting correction is more accurate because of the wavefront measurements.

► The 30-Second Refraction compensates for the fact that refractive power changes as the pupil expands or constricts. The 3-D Wave assesses sphere, axis and cylinder in three different optical zones at once: 2.6 mm, 3.0 mm, and 5.0 mm. The software then uses classic vector-analysis formulas to combine the information into a single correction. According to Marco, the result is the most accurate optical prescription currently available.

The 30-Second Refraction also maintains two of the key benefits of an autorefractor: The entire visual system is measured both simultaneously and objectively. But there's no trade-off in accuracy.

Marco recommends using an automated refractor or phoroptor to confirm that the patient prefers the new prescription, and to refine the spherical component, if necessary. (Even if the new correction is more accurate, some patients may prefer the older one.) The new correction can be downloaded to an electronic refractor (such as Marco's Epic 2100) via a tape printout from the 3-D Wave, or dialed into a manual phoropter.

Once the data is entered into a refractor/phoropter, it only takes seconds to finalize the refraction and obtain subjective approval from the patient. (The Epic will let you compare another prescription, such as the patient's current pair of glasses, with the 30-Second Refrac-tion by simply pressing a button.)

How Accurate Is It?

The 3-D Wave can measure sphere ranging from -20.00D to +22.00D and cylinder up to ±12.00D. As with any light-based measuring system, the 30-Second Refraction is affected by opacities and the cooperation of the patient. Doctors report successful readings in about 80% of patients.

How does the 30-Second Refraction stack up against the traditional alternatives?

► Studies have found that the 3-D Wave autorefraction is very close to a subjective refraction. A comparative study of 200 eyes conducted by David Wallace, M.D., at LA Sight in Los Angeles, Calif., found the following average disparities between subjective manifest and the 3-D Wave: sphere: -0.01D; cylinder: 0.01D; axis: 0.21°.

Another comparative study of 101 eyes conducted by Brian Boxer-Wachler, M.D., at the Boxer-Wachler Vision Institute in Beverly Hills, Calif., found the following disparities: sphere: 0.06D; cylinder: 0.09D; axis: 2°.

► Both of these studies found that more than 90% of patients accept the new prescription without changes. They also found that when compared with the final subjective manifest, 80% preferred the 3-D Wave autorefraction or could distinguish no difference.

► Practices that have implemented the 30-Second Refraction report that 90% of patients prefer it to their current prescription.

Feedback from the Field

David Raub, COT, clinical director at The Eye Center, Inc. in Florissant, Mo., has been refracting patients for 27 years; he's used the 3-D Wave for about 6 months. (He has no financial interest in Marco or the 3-D Wave.)

"I've used many autorefractors over the years, and this far exceeds their accuracy," he says. "With the older autorefractors, we'd be lucky to get an accurate reading 50% of the time. We're finding that the 30-Second Refraction has an 80% to 90% accuracy rate, which is better than some technicians. This is re-flected in our remake rate, which is less than the national average of 5%.

"I input the correction into my Epic 2100 system, which allows me to compare the patient's current glasses with the new prescription. Patients like the new refraction 80% to 85% of the time. If they choose the new refraction, I bump the spherical component up and down 1/2 D or 1/4 D, and we're done.

"If the patient is very cooperative, I can do the refraction in less than 30 seconds. I still like to spend another minute or two doing a quick manifest over that, to confirm the refraction and make sure the patient is happy. Either way it's much faster than the old method."

John P. Goltschman, M.D., who practices at The Eye Center, agrees. "The time required to refine the refraction is reduced substantially, which leverages tech time and doctor time. Increased practice efficien-cy means increased productivity."

"Having this resource available makes my job easier," says Raub, "especially if I have an extra-heavy load, or a staff member is out sick. I feel confident that I'm going to get an accurate refraction."

A Host of Benefits

Being able to refract more patients quickly -- with reliable accuracy -- can result in a more pleasant patient experience, better patient flow, fewer spectacle re-makes and increased revenue from patients who prefer the new prescription to current glasses.

To find out more about the 3-D Wave, visit www.marcooph.com on the Web, or call (800) 574-8274 and ask for your Area Manager.