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Calculating the error in refractive error
R H Taylor1, R B Ellingham, S Subramaniam
1York Teaching Hospital NHS Foundation Trust, York, UK. robert.taylor@york.nhs.uk
Aims And Purpose:
To demonstrate a quick way of calculating the optical difference between two refractions using vector analysis, and to express this as a score for examination purposes.
Methods:
An existing formula is applied, converted to a defocus equivalent, and then converted to a score. The formula is set out in an Excel spreadsheet.
Results:
The spreadsheet enabled rapid assessment of the difference between two refractive errors. Examples are demonstrated.
Conclusion:
The spreadsheet was successful in enabling a comparison of any two refractions, expressing the difference either as a correcting (third) refraction, a defocus equivalent or a one-figure score.
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