Aberration correction with soft contact lens: is the postlens tear film important?

A number of factors may influence the performance of soft contact lenses designed to correct the aberrations of the eye. Although the effect of many of these factors has been investigated, the effect of postlens tear film has not. We estimated the optical effect of the postlens tear film by using simplified models of postlens tear thickness profiles.

Three models were analyzed, including (1) a worst-case scenario before lens settling, (2) representative components of thickness profile based on Zernike-like forms, and (3) a series of undulations (ripples) across the postlens tear film. A range of thicknesses of the tear film was studied. Ray-tracing analyses were conducted on all models to calculate the modulation transfer function response between 0 and 100 cycles per degree and Strehl ratio.

The results show that in only a few scenarios does the reduction in optical performance because of the postlens tear film approach those introduced by conventional spherical surface soft contact lenses.

The postlens tear film can introduce discernable amounts of optical degradation in the lens-wearing eye. However, the amount of this effect is likely to be small compared with other sources, and benefits afforded by the use of aberration-corrected soft contact lenses should not be severely affected.