The validity and reliability of the handheld SW-100 autokeratometer

Abstract

Background: The agreement of new instruments or clinical tests with other instruments or tests defines the possibility of these being used interchangeably. Aim: To investigate the validity and reliability of the SW-100 autokeratometer using a Bausch & Lomb (B & L) keratometer as the 'gold standard'. Methods: Eighty subjects (80 right eyes) aged between 21 and 38 years were recruited. For intra-test repeatability, two measurements of the corneal radius of curvature were taken with the SW-100 and B & L keratometers. Forty of the 80 subjects participated in the inter-test repeatability measurement. Results: Corneal radius of curvature was found to be statistically different between the two instruments (p < 0.001), with the SW-100 providing slightly flatter values of 0.11 mm and 0.05 mm for the horizontal and vertical meridians, respectively, than the B & L keratometer. The average corneal curvature was 0.07 mm flatter with the SW-100 autokeratometer than with the B & L device. Agreement between the SW-100 and B & L keratometers' axes was 45% within ± 5°, 60.3% within ± 10°, 78.8% within ± 15°, 80.3% within ± 20°, and 88.7% within ± 40°. Intertest repeatability was better for the B & L device than the SW-100 and showed no significant difference between the two sessions. Both instruments demonstrated comparable intrasession repeatability. As such, both instruments were comparatively reliable (per coefficients of repeatability). The range of limits of agreement of ± 0.14 mm (horizontal meridian) and ± 0.17 mm (vertical meridian) between the SW-100 and B & L devices showed good agreement. Conclusion: The results suggest that the SW-100 autokeratometer is a reliable and objective instrument that, however, provides flatter radii of curvature measurements than the B & L keratometer. A compensating factor incorporated into the instrument could reduce the difference between the two instruments and make them more interchangeable.