Repeatability of in vitro power profile measurements for multifocal contact lenses

• Power profiles were measured with high repeatability values.
• The repeatability was homogeneous along the optical zone.
• Three measurements of the power profile are needed to get a tolerance of 0.05 D.

PurposeTo evaluate the repeatability of an optical device (NIMO TR1504, Lambda-X, Belgium) for measuring multifocal contact lens power profiles.MethodsThe NIMO TR1504 was used to measure power profiles 30 times for each of 10 different contact lenses from 4 major companies. All contact lenses were labelled as −3 D for distance vision; half were for high addition and half for low addition. The optical zone in all measurements was set to 3-mm radius. For each lens, the median power profile and the residuals of the 30 measurements were calculated. The 95% confidence bands and two indices that summarize measurement errors were calculated: the repeatability limit and an index of repeatability heterogeneity, quantifying heterogeneity of measurement errors over the optical zone.ResultsThe repeatability limit was good (from 0.04 D to 0.12 D), for all multifocal contact lenses. Variability of measurement errors of power profiles was quite homogeneous along the optical zone for all lenses, although for some lenses variability was slightly higher in the centre than peripherally.ConclusionsThe repeatability of measured power profiles obtained by the NIMO TR1504 is lower than 0.12 D for the multifocal contact lenses.