Comparison of Refractive Error Measurements between KR-1W Wavefront Analyser and KR-8800 Automatic Refractometer in School Children NC09-NC12
Dr. Xiaogang Wang,
Consultant, Department of Ophthalmology, Shanxi Eye Hospital, No. 100 Fudong Street, Taiyuan-030002, China.
Introduction: A number of methods and instruments, such as retinoscopy, Hartmann-Shack sensor, ray tracing method and rotary prism technology, are available for assessing refractive status in clinic. The literature on comparison of refractive error values between KR-1W wavefront analyser and KR-8800 automatic refractometer is not adequately available.
Aim: To compare refractive error measurements taken by KR- 1W wavefront analyser and KR-8800 automatic refractometer and study factors influencing the refractive error values, such as age and gender.
Materials and Methods: As a prospective observational study, one eye of 57 school children underwent refractive error measurements with the sequence of KR-8800 and KR-1W with the time interval less than five minutes under no cycloplegic condition. The interdevice agreement was evaluated using the Bland-Altman analysis, Pearson correlation coefficient, and paired two-tailed t-test. Vector analysis was used to compare astigmatism measurements.
Results: The spherical power values measured by the KR8800 were significantly more negative about 0.16±0.51 diopter than those of the KR-1W (p=0.024). The cylinder power values measured by the KR-8800 were significantly more positive about 0.11±0.32 diopter than those of the KR-1W (p=0.014). Moreover, KR-8800 and KR-1W were significantly different in astigmatism measurements using vector analysis. There was a significant linear correlation between the KR-8800 and KR-1W instruments for the spherical error (r=0.974, p<0.0001), cylinder power (r=0.807, p<0.0001). The interdevice 95% Limits of Agreement (LoA) range for the spherical error and cylinder power were 2.02 D and 1.25 D, respectively. Age negatively correlated with spherical error and cylinder power and the spherical error showed much more negative correlation values than cylinder power. However, gender showed no significant correlations with neither spherical error nor cylinder power of both instruments.
Conclusion: The spherical power and astigmatism showed significant difference between the KR-1W and KR-8800 devices. However, the measurements of the two instruments showed significant linear correlation to each other.