Refractive power profiles of soft rotationally symmetrical contact lenses as a function of aperture diameter

Purpose. The aim of the study was to measure and to compare the power profiles of market-leading single vision and multifocal soft contact lenses.

Material and Methods. A high-resolution instrument based on the phase-shifting schlieren method (NIMO TR1504, Lambda-X, Belgium) was used to measure the optical power distribution of single vision and multifocal contact lenses with −3.00 D, −6.00 D, −9.00 D and +3.00 D. The optical power of the single vision lenses was measured at six different aperture diameters ranging from 2.0 mm to 7.0 mm in steps of 1.0 mm. Each multifocal design was measured with an aperture of 7.0 mm. A total of 200 contact lenses was measured, five lenses per power and type.

Results. All single vision contact lenses with negative back vertex power showed a negative increase in lens power with increased distance from centre. The changes in power between the central and peripheral aperture were statistically and clinically significant for every negative refractive power and type (p < 0.05). Etafilcon A showed the highest negative increase with greater apertures with values up to 1.19 ± 0.04 D. Lotrafilcon A showed overall the least deviation with maximum values of 0.61 ± 0.05 D. Each type of multifocal contact lens exhibited different power profiles. The profiles were very consistent across all negative back vertex powers.

Conclusion. As expected, the negative single vision contact lenses exhibited an increase in lens power towards the periphery due to spherical aberration. Greater aberration resulted in a higher negative deviation. The analysis of power profiles of multifocal lenses provides valuable information for fitting lenses for presbyopes considering their pupil size.