Optical Characterization of Multifocal Contact Lenses Used for Myopia Control

Purpose: Center-distance multifocal contact lenses (MFCLs) are widely used for myopia management. The MFCL designs incorporates peripheral addition power based on the peripheral defocus hypothesis for myopia control. Each MFCL has a distinct optical pro file, and pupil size may influence their effectiveness by altering the extent and location of peripheral defocus. However, the combined effects of MFCL design and pupil size on peripheral defocus remain unclear. This study aimed to characterize MFCL optics, assess their impact on peripheral defocus, and evaluate how pupil size affects myopia inhibition stimulus.

Methods: Power profiles for the four MFCLs were measured using a power-mapping instrument (NIMO TR1504, Lambda-X). Peripheral refraction and peripheral defocus with four MFCLs were measured in 21 myopic subjects at various eccentricities using the WR-5100K autorefractor. MFCL power profiles were compared to assess their optical differences and influence on peripheral defocus. Custom MATLAB software incorporating pupil segmentation algorithms was used to compute Modulation Transfer Functions (MTFs) and Visual Strehl ratio of the Optical Transfer Function (VSOTF) for pupil sizes from 0.5 to 7.5 mm. These metrics quantified the MFCLs ability to produce myopic defocus across pupil sizes and eccentricities.

Results: While MFCL brands use different designs, each brand’s design remains consistent across its power range. Lens design significantly affected peripheral defocus, even with identical labeled addition powers. VSOTF curves at the fovea showed that pupil size modulates peripheral defocus. MTF curves indicated reduced myopic defocus at greater eccentricities for all lenses. Each lens demonstrated a unique profile with optimal performance at specific pupil sizes. Pairwise comparisons revealed design-specific ad vantages under varying pupil and defocus conditions.

Conclusion: Peripheral defocus, pupil size and MFCL design should all be carefully consideration when prescribing MFCLs for myopia control.