Profilometric Measurements For Analysis Of The Optical Performance Of Multifocal Intraocular Lenses

Lens surface manufacturing control has become a key factor in optical and clinical characteristics of the Multifocal Intraocular Lenses (MIOLs). Among other parameters, the Modulation Transfer Function (MTF) and its derivative MTF through-focus curve are commonly used to evaluate the optical performance of MIOLs. MTF is usually obtained from optical bench measurements according to ISO standard recommendations.The aim of this study was to develop a new methodology, based on surface profilometer measurements to assess the optical behaviour of MIOLs. From these measurements the “Modulation Transfer Function through-object” (MTF through-object) based on vergence object displacement was calculated for different pupil sizes and pseudophakic eyes.

University of Alicante (Spain)

Tecnis Eyhance, RayOne EMV, Tecnis Symfony, Mini Well and Tecnis Synergy were analyzed. The surface the IOLs was measured with an optical profilometer. After a smoothing process of the raw data and using Zemax and Matlab programs the entire simulation process, including ray tracing and results analysis, was carried out. The MTF through-object curve was obtained by calculating the MTF value for 50 cycles/mm, in image space and changing the object vergence. Calculations were conducted for two model eyes (aberrated and not aberrated cornea) and two pupil sizes. For comparison between the different IOLs, an optical quality criterion based on a minimum value the MTF through-object and the recognition of simulated vision optotypes was introduced.

The initial step involved comparing our proposed methodology with previously published methodologies, consistently achieving comparable results throughout the comparison. Although the shape of MTF through-focus and through-object were similar, the MTF through-object was narrower providing further near and intermediate points distances and lower depth of focus around far peak. The optical behaviour of IOLs depended on the eye model and pupil size. A decrease of the Spherical Aberration (SA) produced a hypermetropic shift of the far focus between +0.3 D and +0.4 D. Most of IOLs worsen the optical quality as pupil size increased, even the MTF through-object shape changed.

A methodology based on profilometer measurements proved to be comparable with other methodologies for assessing the optical quality of IOLs. By means of this methodology, the MTF through-object, based on the vergency object change, was proposed to analyze the optical behavior of IOLs. This study shown new results, as MTF through-object curves have never been reported before with the IOLs analysed. The results have a major implication for clinical practice since they will be more consistent with, for example, clinical defocus curves. Variations in corneal aberrations and pupil size led to significant shifts in IOL behavior, manifesting in alterations to the shape of the MTF through-object.