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A clinical comparison of subjective autorefractors to conventional refraction

1 May 1993


The performance and cost effectiveness of two automatic refractors with subjective refinement capability was evaluated. Using a group of 125 patients, the results of the objective autorefraction and its subjective refinement by a technician were compared to the results of a conventional subjective examination. The objective autorefraction spherical equivalent differed from the conventional subjective by 0.50 D or less in 72% of eyes for the Humphrey 570, and 85% of eyes for the Marco 1600. The subjective refinement of the autorefraction resulted in a spherical equivalent difference of 0.50 D or less in 80% of eyes for the Humphrey and 84% of eyes for the Marco. The cylinder power difference was similar for both instruments and was 0.50 D or Jess in 82% of all eyes for objective autorefraction and 89% after subjective refinement. Objective autorefraction axis differences were generally small and were also similar for both instruments. There was no improvement in axis accuracy after subjective refinement. While subjective refinement did improve the accuracy of the autorefractors, the improvements were modest and probably not significant from a clinical standpoint. Even with subjective refinement, the instruments yielded large errors for some eyes. A cost analysis revealed the following: for a military clinic seeing 2000 patients per year, the autorefractors must save the practitioner 5.3 minutes per exam to be cost effective. This dropped to 3.6 minutes for the Marco, and 3.8 minutes for the Humphrey for a clinic seeing 6000 patients per year. If the instrument saves less than 3 minutes of examination time, then the technology is not cost effective regardless of patient volume.


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