Diffractive Soft Contact Lenses for Modifying Ocular Longitudinal Chromatic Aberration

Childhood myopia prevalence is increasing rapidly worldwide, underscoring the need for effective strategies to slow its progression. Longitudinal chromatic aberration (LCA) has been identified as an optical cue for the sign of defocus that may guide childhood eye growth and emmetropisation. Reversing the sign of ocular LCA has been proposed as a myopia control strategy, yet no wearable devices have demonstrated this capability. Here, diffractive soft contact lenses fabricated using laser-induced refractive index change (LIRIC) are introduced to modify ocular LCA.

Contact lenses were made with four diffractive powers (1.5, 2.0, 3.0 and 6.0 D) using LIRIC, a femtosecond laser writing technique that modifies the internal refractive index of a soft contact lens without altering external geometry. Lens LCA was characterised using a custom multi-wavelength Badal optical bench with narrow bandpass filters (470, 532, 550, 630 and 700 nm). LCA was defined as the linear slope of relative optical power versus wavelength (D/μm). Theoretical predictions were derived from a first-order thin lens model using the negative Abbe number of diffractive wavefronts (-3.45).

Measured LCA values of the lenses were 2.77, 3.78, 5.31 and 11.37 D/μm for LIRIC lenses of 1.5, 2.0, 3.0 and 6.0 D of diffractive power, respectively, in close agreement with theoretical predictions (2.73, 3.64, 5.45 and 10.91 D/μm). Theoretical modelling of a diffraction-limited eye with average human LCA predicted that the 1.5 and 2.0 D diffractive designs partially compensated the eye's native LCA, the 3.0 D design minimised it and the 6.0 D design reversed its sign.

This study presents the first demonstration of a soft contact lens capable of manipulating ocular LCA, including sign reversal. LIRIC diffractive contact lenses offer a practical platform for tuning the eye's chromatic defocus cues and warrant further investigation as a novel myopia control strategy.