1. Prospective Comparison of Manifest Refraction with Autorefraction Before and After Sub-Bowman Keratomileusis
Joel D. Hunter MD
Frank Schwendeman OD
Daniel S. Durrie MD
Durrie Vision
Overland Park, KS

2. Potential Conflicts of Interest
Drs. Hunter and Schwendeman have no financial relationships to disclose
Presently Dr. Durrie is a clinical investigator for:
Alcon
Allergan
AMO
Bausch and Lomb
IntraLase
Refractec
Acufocus
WaveTec
Avedro
Encore Vision
LenSx
Wavefront Science
NeuroVision
High Performance Optics
OcuSense
QuestVision
Visiometrics
Tracey Technologies
Topcon
Ocular Optics

3. Purpose
To evaluate accuracy of autorefraction compared with manifest refraction
To investigate whether the traditional phoropter is still the “gold standard” for accurate pre- or post-operative evaluation in a refractive surgery practice

4. Study Design
3-month prospective clinical trial includes 300 eyes at pre-operative, 1-month and 3-month post-operative visits for Sub-Bowman Keratomileusis
Myopia or hyperopia with or without astigmatism were treated with SBK using the IntraLase for flap creation and the Allegretto Wavelight for ablation.
Two consecutive measurements at each visit:
Nidek ARK-530A
Topcon KR-8800
Nidek OPD-Scan II

5. Results - Accuracy
These results are concerned with how far away the patient's average autorefraction is from the "true" value (manifest)
Because refractions are a combination of sphere and cylinder, comparison can only be done by vector analysis
Vector manipulations were used to determine the error

6. Autorefractor vs. MRx Histograms

7. Autorefractor vs. MRx Double-Angle Plots

8. Results - Repeatability
These results are concerned with the difference between the values of the 1st and 2nd measurement on the same device
The “distance” between the measurements was based on the magnitude of the vector difference between measurements (i.e. vector analysis)

9. Results - Repeatability
Manifest Refraction – most disparity
Spherical Equivalent: 0.17 D
Cylinder: 0.23 D
Nidek ARK-530A – least disparity
Spherical Equivalent: 0.07 D
Cylinder 0.11 D
Topcon KR-8800
Spherical equivalent: 0.12 D
Cylinder: 0.12 D
OPD-Scan II
Spherical equivalent: 0.14 D
Cylinder: 0.15 D

10. Interpretation
Modern autorefraction is within 0.27 D of spherical equivalent and 0.32 D of cylinder or less, depending on the device used, when compared to manifest refraction.
Modern autorefraction is highly repeatable, with spherical equivalent and cylinder changes averaging <0.25 D for all three machines tested.