Method of determining a patient's subjective refraction based on objective measurement

PURPOSE: To develop a method for predicting the manifest refraction from objective measurement using wavefront sensing. We tested the hypothesis that, when the eye has an optimal refractive correction, the refractive power of the eye is in the most stable state, with the least fluctuation in its total optical aberration and hence least amount of standard deviation in the wavefront error. METHODS: Nine patients were enrolled in this study. All measurements were performed using a grating-based wavefront instrument manufactured by Ophthonix, Inc. The test procedure involved adding defocus power binocularly in the line of sight of the patient. Five added diopter powers were used: plano (no add), +1.00 D, +0.50 D, -0.50 D, and -1.00 D. The eyes were undilated, and the measurement was taken at a single added defocus power each day over 5 days. The patients had a binocular view and were asked to focus on a picture at 20 feet. Manifest refraction was used as the reference point (the added powers are relative to this "plano" power). RESULTS: For each patient, the standard deviation (STDEV) of the total root mean square values of the wavefront measurement were used as a measure of vision fluctuation. Spherical equivalent manifest refraction was tested against the added defocus as a measure of the method's predictability. Graphic plots of standard deviation of the total wavefront error against the added diopter power showed that the minima of the vision fluctuation from the data sets were within -0.10 and +0.30 D (95% limit of agreement). The mean difference between the manifest refraction and the most stable point of vision was 0.14 D. CONCLUSIONS: The preliminary results of 10 eyes show promise that using an objective method of monitoring vision fluctuation may produce good agreement with the manifest refraction. The method should be further validated using a smaller step of added defocus and involving a larger number of test subjects representing a sample of the general population.