Author: Eleni Papadatou, University of Valencia
Background: Life’s expectancy increment will lead a great part of the population in spending almost half of their lives being presbyopes. Spectacle correction is the most common solution for presbyopia compensation but current lifestyle and aesthetics drive new presbyopes to other correcting techniques. Simultaneous vision multifocal contact lenses seem an appealing solution although the fitting rates are still relatively low.1 The concept of these designs is the projection of both in-focus and out-of-focus images at the same time and their success relies on the visual system’s ability to suppress the blurred out-of-focus images (regarding the viewing distance).2 Under in-vitro experimental conditions, power profiles3,4 of these lenses can give important information about the power distribution across their optical zone.
Study: In this study, we studied different types of simultaneous vision multifocal contact lenses (center near and center distance designs, different addition powers). By using a power mapping device (NIMO TR1504, LAMBDA-X, Belgium) the power profiles of the lenses were obtained for a 6 mm pupil size. Based on their power profiles we calculated the proportions of power distribution for different pupil sizes, i.e. 3 mm, 4.5 mm and 6 mm (Figure 1).
Figure 1: power distribution (%) of a center near multifocal contact lens at three different pupil sizes. The nominal power of the lens was -3.00 D.
Additionally, we divided the power profiles into different distance zones (far, intermediate and near with respect to the nominal power of the lenses) and we calculated the proportion of the area of lens’ surface dedicated to each zone as function of pupil size (Figure 2).
Figure 2: example of calculation of the area of the lens dedicated for near zone (right figure) as a function of pupil size. In this case the lens is of center near design. In left graph, which illustrates the power profile of the lens, the dashed lines indicate the thresholds between far, intermediate and near vision zones (in respect with the nominal power of the lens which was -3.00 D).
Summarizing, the two basic findings of the study were that the resulting refractive power at a given pupil size relies on the design of the lens and its addition power and that all the 3 lenses types we studied, regardless their design, enhanced intermediate vision at moderate pupil sizes. This study has been submitted as an original paper work and is currently evaluated by a peer reviewed scientific journal.
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- Madrid-Costa D, Ruiz-Alcocer J, García-Lázaro S, Ferrer-Blasco T, Montés-Micó R. Optical power distribution of refractive and aspheric multifocal contact lenses: Effect of pupil size. Cont Lens Anterior Eye 2015; 38:317-21.
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