Background. Contact lenses may be optimised to correct for the aberrations of the eye and provide superior vision. However, due to various requirements, soft contact lenses (SCL) are deliberately fitted to be different from the shape of the eye. As a consequence, SCL will distort when placed on the eye in the clinical phenomenon known as the Lens Flexure Effect (LFE). The defocus effect of LFE has only been studied previously but little is known about its effect on aberrations. With the current intentions to correct aberrations using SCL, the effect of LFE on higher order aberrations becomes important. Method. We used finite element analysis (ANSYS) to investigate the shape change of SCL placed on eye. We transferred the output as sixteenth order even polynomials into a ray-tracing program (Zemax) to evaluate the optical performance of the pre-flexed and post-LFE SCL. A range of SCL base-curves (BOZR, 7.0 mm to 9.0 mm in seven steps) and back vertex powers (BVP, -12D to +3D in seven steps) were studied to look at the impact of these parameters on LFE. Results. Effect of LFE of BVP increases with BVP and departure of BOZR from corneal shape. However, within clinically practical values, the impact is small (around 0.5D). LFE also has an impact on spherical aberrations although its impact is varied according to BVP and BOZR. Conclusion. The optical impact of SCL LFE can be predicted using computation modelling. LFE may limit the performance of some designs of aberration-corrected SCL.
"Finite element modeling of soft contact lens flexure and aberrations", Proc. SPIE 5314, Ophthalmic Technologies XIV, (13 July 2004); doi: 10.1117/12.537918; https://doi.org/10.1117/12.537918