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Evaluation of an automated subjective refractor
James Sheedy1, Paul Schanz, Mark Bullimore
1The Ohio State University, College of Optometry, Columbus, Ohio 43218, USA. sheedy.2@osu.edu
Purpose:
To test the validity and repeatability of an automated subjective refractor compared with subjective refraction performed by clinicians. Corrected visual acuity was used to compare the validity of each technique.
Methods:
On each of two visits separated by at least 1 week, the following were measured in 60 naive subjects (mean age, 33 +/- 11 years): automated objective refraction (AOR) and automated subjective refraction (ASR) with the Topcon BV-1000, subjective refraction by one of two doctors (DR), and monocular visual acuity with the ASR and DR findings. Repeatability of refraction was calculated as the 95% limits of agreement (LoA) between same-mode measurements from the two visits. The validity of the ASR compared with DR was determined two ways: as the 95% LoA between the two measures and as the mean visual acuity measured with each prescription.
Results:
The DR and AOR had similar repeatability: 95% LoA = -0.49 to +0.46 D and -0.51 to +0.45 D, respectively. The ASR had poorer repeatability with 95% LoA of -0.70 to + 0.71 D. Because of a calibration (offset) error in the right eye path of the BV-1000, the ASR of the right eye yielded refractions +0.26 +/- 0.41 D higher than the DR. For the right eye, visual acuity was 3.42 +/- 6.09 letters better with the DR than with the ASR, consistent with this calibration error. For the left eye, visual acuity was 1.20 +/- 5.20 letters better for the DR.
Conclusions:
Doctor-performed refractions are more valid and repeatable than the ASR performed with the BV-1000, although the differences are small. When calibrated, the BV-1000 gives similar visual acuity values to the DR, although the visual acuity for the DR is more repeatable.