Objective assessment of the effect of pupil size upon the power distribution of multifocal contact lenses

AIM： To analytically assess the effect of pupil size upon the refractive power distributions of different designs of multifocal contact lenses.METHODS： Two multifocal contact lenses of center-near design and one multifocal contact lens of center-distance design were used in this study. Their power profiles were measured using the NIMO TR1504 device （LAMBDA-X, Belgium）. Based on their power profiles, the power distribution was assessed as a function of pupil size. For the high addition lenses, the resulting refractive power as a function of viewing distance （far, intermediate, and near） and pupil size was also analyzed.RESULTS： The power distribution of the lenses was affected by pupil size differently. One of the lenses showed a significant spread in refractive power distribution, from about ？3 D to 0 D. Generally, the power distribution of the lenses expanded as the pupil diameter became greater. The surface of the lens dedicated for each distance varied substantially with the design of the lens.CONCLUSION： In an experimental basis, our results show how the lenses power distribution is affected by the pupil size and underlined the necessity of careful evaluation of the patient’s visual needs and the optical properties of a multifocal contact lens for achieving the optimal visual outcome.

Repeatability of in-vitro optical quality measurements of intraocular lenses with a deflectometry technique effect of the toricity

AIM： To evaluate the repeatability of an optical device for measuring the Zernike coefficients of toric intraocular lenses（IOLs） and assess whether its toricity has any impact in its repeatability. METHODS： An experienced technician used the NIMO TR1504 to measure the Zernike coefficients 30 times for an aperture of 4.50 mm for all lenses included. The IOLs included were divided into two group： toric and nontoric ones. The cylindrical powers of the toric lenses included in the present study were 1.00, 1.50, 2.25, 3.00 and 3.75 D. Finally, the repeatability of the NIMO TR1504 was described in terms of within subject standard deviation（Sw） and repeatability limit. RESULTS： The Sw was smaller than 0.011 μm for both lens groups and all Zernike coefficients, and the difference between both groups was smaller than 0.004 μm for all Zernike coefficients. Regarding the repeatability limit, this value was smaller than 0.025 μm for the toric lens group, and smaller than 0.031 μm for the non-toric lens one for all Zernike coefficients. Furthermore, the maximum difference between both lens groups was 0.010 μm. CONCLUSION： The repeatability of the NIMO TR1504 to measure the optical quality is high and independent of the lens toricity. These results reflect that this system is robust and could be used to measure the in-vitro optical quality of either toric or non-toric IOLs.