Standardized patient methodology to assess refractive error reproducibility

Optom Vis Sci. 2009 May;86(5):517-28. doi: 10.1097/OPX.0b013e31819fa590.


Purpose: Standardized patient (SP) methodology is the gold standard for evaluating clinical practice. This approach was used to investigate the content of typical optometric eyecare in England and the reproducibility of refractive error measurement using prescriptions obtained by three SPs.

Methods: The three SPs were independently examined by three to four expert optometric clinicians to obtain "benchmark" estimates of refractive error. One hundred two community optometrists consented to be visited by three SPs who were trained to provide accurate responses during the examinations. The spectacle prescriptions obtained by the SPs were analyzed for spherical equivalent refraction, spherical power and cylindrical power using astigmatic decomposition.

Results: The spherical equivalent refractions were found to be within +/-0.25 D of the benchmark on average 81% of the time and within +/-0.50 D 97% of the time. The spherical power was within +/-0.25 D 90% of the time and within +/-0.50 D 98% of the time. The cylindrical power agreed within +/-0.25 D 93% of the time and within +/-0.50 D 100% of the time. Based on reproducibility limits data obtained for all six eyes, any two optometrists would differ in their estimation of spherical equivalent refraction by no more than 0.75 D in 95% of repeated measures. The astigmatic data (C0 and C45) show that optometrists will differ in their estimation of the C0 component by between 0.25 and 0.61 D and for the C45 component by between 0.22 and 0.47 D in 95% of repeated measures.

Conclusions: The agreement between our data and the results of other similar studies support the conclusions that subjective refractive findings are reproducible to approximately +/-0.75 D when performed by multiple optometrists in patients of different age groups and levels of ametropia. SPs are an effective way of measuring reproducibility of refractive error and should be considered for further comparative analysis in different age groups and different levels of ametropia.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Astigmatism / diagnosis
  • England
  • Optometry / standards*
  • Prescriptions / statistics & numerical data
  • Refractive Errors / diagnosis*
  • Refractometry / methods*
  • Reproducibility of Results