Article Date: 7/1/2004

instrumental strategies
The "30-Second Refraction"
This refraction system is not only faster but more accurate.
LOUIS J. CATANIA, O.D., F.A.A.O.; JOEY MENDOZA, C.O.A.; AND JULIE PALMER, C.O.M.T.

Experts view wavefront analysis as the most substantial eyecare technological advancement "so far" in the 21st century. At its highest level, clinicians use wavefront technology for diagnostic testing in vision and ocular surface disorders and now, specifically in routine refraction.

Because wavefront technology accurately measures lower and higher order aberrations, we can define the combined influences of 2nd order defocus (sphere) and regular astigmatism with 3rd and 4th order coma, trefoil, spherical aberrations and the irregular astigmatism they produce. This capability uniquely provides a more refined and precise spectacle correction, even when stated in lower order terms alone, due to the optimal computer calculated accuracy of the cylinder power and axis.


Vector analysis combines 2nd, 3rd and 4th order aberrations to determine a single, precise astigmatic correction.

A single, precise correction

The 3D Wave by Marco, a commercially available dynamic spatial skiascopy wavefront aberrometer, can achieve a wavefront-guided, higher order spectacle prescription. The instrument's software uses classical vector-analysis and complex optical formulas to blend multiple cylinders (from 2nd, 3rd and 4th orders) into a single, precise astigmatic correction. The power and axis of this resultant cylinder combined with lower order defocus terms is the most accurate optical prescription obtainable for the human eye.

Downloading this computer- generated prescription information from the 3D Wave to an electronic refractor, or dialing the information into a manual phoropter will provide fast and accurate access to an objective optical prescription. As purely optical corrections are not always "exactly" what the visual cortex will accept, some level of subjective verification for any such prescription is always valuable.

Verification is easy

By a simple subjective testing through + 0. 25/- 0. 25 bracketing of the defocus term, you can identify the final sphere. Also, notwithstanding the precision of the cylinder power and axis, a comparison with the patient's previous prescription (achieved by pressing a button on an electronic refractor to alternate between the new prescription and the original prescription downloaded from the lensometer) would confirm cortical acceptance of the astigmatic component. Because of the efficiency, speed and accuracy of this unique refractive approach, Marco terms the concept the "30-Second Refraction."

High patient acceptance

Studies and experience using the 30-Second Refraction in our practice, as well as additional studies, show that this wavefront-guided refractive technique yields greater than 90% patient acceptance with no changes necessary in the downloaded prescription.

As many as 40% of patient's consider the downloaded 30-Second Refraction prescription superior to their standard subjective manifest refraction. These levels of acceptance ratify the accuracy of a wavefront-generated prescription.

The 90% acceptance of the 30- Second Refraction is understandable based on the science and the comprehensive nature of the wavefront-generated refractive information. The 40% "preference" of the 30-Second Refraction prescription indicates the value of a blended astigmatic correction in the average 4 to 5 mm pupil and under mesopic and scotopic conditions.

The 10% solution

In the 10% of cases where the patient prefers another prescription, the visual cortex has likely adapted to or "learned" a different (albeit potentially less accurate) astigmatic correction than the wavefront-generated, vector-analyzed power and axis. In these cases, a full manifest subjective refraction including Jackson cross-cylinder testing is required.

Essential for a busy practice

Wavefront analysis has introduced a technology that can now provide not only a significantly faster method of refraction, but a more accurate refraction for greater than 90% of our refractive patients.

This profound improvement in the efficiency and precision of refractive care, along with the rapidly growing list of other diagnostic uses for wavefront technology in vision and eye care, make the wavefront aberrometer an essential tool in the armamentarium of any busy eyecare practitioner.

References available on request.

DR. CATANIA, A MEMBER OF THE OM EDITORIAL ADVISORY BOARD, IS A WORLD RENOWNED CLINICAL EDUCATOR ON ANTERIOR SEGMENT AND NEW TECHNOLOGIES. HE IS ASSOCIATED WITH NICOLITZ EYE CONSULTANTS IN JACKSONVILLE, FL.

MR. MENDOZA AND MS. PALMER ARE SENIOR TECHNICIANS WITH NICOLITZ EYE CONSULTANTS IN JACKSONVILLE, FL. THEY ARE SKILLED IN COMPUTERIZED REFRACTION AND WAVEFRONT ABERROMETRY.


Optometric Management, Issue: July 2004