Clinically relevant measurement conditions and metrics for evaluating intraocular lenses

Abstract

Purpose : According to ISO standard for intraocular lenses (IOLs) (ISO 11979-2), IOLs’ imaging quality can be specified as the modulation transfer function (MTF) value measured at one particular spatial frequency in green light. Measurement results of IOLs strongly depend on the conditions in which measurements are performed. Additionally, IOL material and design influence chromatic aberration, that impacts the optical and visual performance of the pseudophakic eye (Weeber et al. ARVO 2016). The purpose of this study was to evaluate the correlation between clinical performance and different MTF based metrics and measurement conditions.

Methods : Through focus MTF was measured using an optical bench for a range of IOL designs, including monofocal, spherical and aspheric, as well as multifocals, with different add powers, and an extended depth of focus IOL. Measurements were performed in white light at 3mm pupil. Three MTF based metrics were evaluated: the area under the MTF (MTFa) calculated up to 50cpmm, as well the MTF measured at 50cpmm and 100cpmm, respectively. In addition, MTF was measured in green light at 50cpmm and 100cpmm, per ISO 11979-2. Each metric was compared to the defocus curves measured in patients bilaterally implanted with the same IOL models. In the clinic, high contrast defocus VA was measured binocularly using the ETDRS chart with best distance correction.

Results : Amongst all the metrics evaluated, the highest correlation was found for MTFa measured in white light (r²=0.95) and the lowest was for both MTF metrics that incorporate one single spatial frequency measured in green light (r²<0.60). The correlation of MTF at 100cpmm increased by a factor of 1.1 when measurements were performed in white light, but remained relatively low (r²=0.67). For MTF at 50cpmm, the correlation was further increased due to white light by a factor of 1.4 as compared to using green light.

Conclusions : MTF based metrics are correlated to clinical performance and the correlation depends on the measurement conditions. An MTF based metric that incorporates multiple spatial frequencies in white light showed a high correlation to clinical performance. MTF measurements performed according conditions of the ISO resulted in limited correlation.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.