1. 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 ICEE 2007 The Inaugural World Congress on Refractive Error and Service Development WCRE 2007 14-16 March, 2007 Durban, South Africa

2. Variability 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” Minimum Variability Maximum Variability 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.

3. The 0.50D Rule Study Examiners SubjectsMeasurements Harvey et al. (1997) 1 47 1 Repeatability Studies 1201McKendrick, Brennan (1995) 1402Johnson et al. (1996) 2401Walline et al. (1999) 1125unspecifiedSalchow et al. (1999) 2401Raasch et al. (2001) 11171Choong et al. (2006) 31001Dave et al. (2004) 2301Elliott et al. (1997) 1862Bullimore et al. (1998) 11001Trusit, Yasufumi (2004) 2602Sheedy et al. (2004) 11901Pesudovs, Weisinger (2004) 2992Leinonen et al. (2006) 1213Sloan et al. (1954) 2402Zadnik et al. (1992) 5121Rosenfield, Chiu (1995)* MeasurementsSubjectsExaminersStudy * SD = 0.14 D, 95% Range 0.55D Reproducibility Studies

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

6. Software courtesy of Harris, Malan, Rubin. Optometric Science Research Group Department of Optometry, University of Johannesburg, P.O. Box 524, Auckland Park 2006 Distribution of Refractive State. Reproducibility Data. 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. Image degrades Subjective endpoint Additional lens power change leads to no improvement in image quality As lens power decreases image quality increases Subject fogged. Image severely degraded The anatomy of a stigmatic self-refraction

9. Dynamics of 20 repeated measures of self- refraction

10. Histogram of Subjective Endpoints Actuator AdSpec

11. Future Directions 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