GE MacKenzie † , JD Silver †† , DN Crosby †† , MJA Newbery † , AK Robertson †

1. ICEE 2007 The Inaugural World Congress on Refractive Error and Service Development WCRE 2007 14-16 March, 2007 Durban, South Africa Repeatability and reproducibility of self-refraction using continuously adjustable fluid-filled spectacle lenses in pre-presbyopes GE MacKenzie†, JD Silver††, DN Crosby††, MJA Newbery†, AK Robertson† †Vision for the Developing World, Nuffield Laboratory of Ophthalmology, University of Oxford, Walton Street, Oxford. OX2 6AW England †† Department of Physics, Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, England Conflict of interest JD Silver: developer of the AdSpec GE MacKenzie: employed by JD Silver

2. Repeatability conditions* “conditions where independent test results are obtained with the same method on identical test items in the same laboratory by the same operator using the same equipment” Implementation of ISO 5725-1:1994. Accuracy (trueness and precision) of measurement methods and results. Part 1: general principles and definitions. BS ISO. Variability MinimumVariability MaximumVariability Reproducibility conditions* “conditions where test results are obtained with the same method on identical test items in different laboratories with different operators using different equipment”

3. Study Examiners Subjects Measurements Rosenfield, Chiu (1995)* 1 12 5 Zadnik et al. (1992) 2 40 2 Sloan et al. (1954) 3 21 1 Leinonen et al. (2006) 2 99 2 Pesudovs, Weisinger (2004) 1 190 1 Sheedy et al. (2004) 2 60 2 Trusit, Yasufumi (2004) 1 100 1 Bullimore et al. (1998) 2 86 1 Elliott et al. (1997) 1 30 2 Dave et al. (2004) 1 100 3 Choong et al. (2006) 1 117 1 Raasch et al. (2001) 1 40 2 Salchow et al. (1999) unspecified 125 1 Walline et al. (1999) 1 40 2 Johnson et al. (1996) 2 40 1 McKendrick, Brennan (1995) 1 20 1 * SD = 0.14 D, 95% Range 0.55D The 0.50D Rule Repeatability Studies Reproducibility Studies Study Examiners Subjects Measurements Harvey et al. (1997) 1 47 1

4. Reproducibility of Subjective Refraction amongst Qualified Optometrists Purpose: To evaluate the reproducibility of subjective refraction Sampling: 40 randomly selected optometric practices - Oxford and the City of Westminster, United Kingdom Measurement independence Trial frame refractions

5. Reproducibility SD = 0.28 D, 95% Range 1.10 D (RepeatabilitySD = 0.14 D, 95% Range 0.55 D) 95% Limits for Residuals over mean refraction

6. Distribution of Refractive State. Reproducibility Data. Software courtesy of Harris, Malan, Rubin. Optometric Science Research GroupDepartment of Optometry, University of Johannesburg, P.O. Box 524, Auckland Park 2006 W. F. Harris (2005) . Reduction of artefact in scatter plots of spherocylindrical data. Ophthalmic and Physiological Optics 25 (1), 13–17.

7. Self-refraction

8. The anatomy of a stigmatic self-refraction Subject fogged. Image severely degraded As lens power decreases image quality increases Image degrades Subjective endpoint Additional lens power change leads to no improvement in image quality

9. Dynamics of 20 repeated measures of self-refraction

10. AdSpec Histogram of Subjective Endpoints Actuator

11. FutureDirections • Similar studies in with large samples of children, pre-presbyopic adults and presbyopic adults Emmetropes, hyperopes and myopes Various degrees of astigmatism • Evaluate feedback control systems used during self-refraction • Study image blur detection, image size, vergence interactions • Optimization of self-refraction protocol