Soft toric lens rotation measurement using Slit-lamp method and built-in camera of smart phone

Purpose: Aims of this study were to investigate the agreement and test-retest repeatability of two methods for measuring magnitude of soft toric lens rotation. The two methods assessed were a newly developed mobile application for iPhone which uses the built-in camera function and the slit lamp biomicroscope. Methods: Agreement of ToriExperta against known reference source was tested under experimental situation. For clinical measurement, thirty three participants (66 eyes) wore toric lens (prism ballast design) both eyes. Two investigators measured toric lens rotation using the two methods which are slit-lamp measurement(HS-700) and mobile application. First investigator used the same method twice for assessment of test-retest repeatability of each method. Inter- and intra-investigator agreement and repeatability were assessed using Bland-Altman analysis. Results: Against the known reference sources, mean variance was 0.52±0.75 degree and limits of agreement was ±1.47 degree (95% of Cls). The limits of agreement between the silt-lamp biomicroscope and mobile application methods was ±9.1 degree (95% CIs). Measurements using the two different methods showed no statistically significant mean difference (paired t-test, p=0.32). Inter-investigator agreement of lens rotation was ±7.9 degree (95% CIs) using the slit-lamp microscope and ±7.8 degree using mobile application. Intra-investigator repeatability was ±6.6 degree using the slit lamp microscope and ±6.8 using mobile application. Conclusions: The results should be considered in view of the fact that soft toric lenses are not static but move with the blink thus the location of the reference point is unlikely to be at exactly the same location at the different measurement times. Despite this source of variability in the results, the newly developed mobile application provides clinically comparable performance to slit lamp biomicroscope measurement which does not appear to be investigator dependent. This mobile application may provide sufficient precision to those optometric practices have limited access to slit-lamp biomicroscope for measuring soft toric lens rotation.