13/07/2015
Author: Eleni Papadatou, M.Sc., University of Valencia
A number of designs regarding contact lenses have been developed in order to improve the vision of the presbyopes. The majority of these designs use the concept of ‘’simultaneous vision’’ which corresponds to lenses that have multiple powers positioned in front of the pupil at the same time. Such lenses, in compare with monofocal lenses, yield more complex power profiles which should be carefully evaluated. Although manufacturers normally provide some parameters for the design of the lenses, yet is not common to provide detailed power profiles.1,2
In order to determine the power profiles of lenses there are several approved methods (ISO 18369) including small-aperture focimetri, Moire deflectometers* and Hartmann-Shack devices. The lab of GIO is equipped with a device based on the phase-shifting Schlieren method which has been demonstrated to be more accurate than the previous ISO mehods.3 Taking advantage of this new technology is possible to obtain the corresponding power profiles of contact lenses.
Using these information, we are able to characterize complex profiles of multifocal contact lenses. Furthermore, we can investigate the effect that various parameters (e.g. pupil diameter) can have on power profiles and how can influence the optical performance.
* First commercial deflectometer: https://www.youtube.com/watch?v=9WLB3tmnmoU
References
1.Plainis, S., Atchison, D. A., & Charman, W. N. (2013). Power profiles of multifocal contact lenses and their interpretation. Optometry & Vision Science,90(10), 1066-1077
2.Montés-Micó, R., Madrid-Costa, D., Domínguez-Vicent, A., Belda-Salmerón, L., & Ferrer-Blasco, T. (2014). In vitro power profiles of multifocal simultaneous vision contact lenses. Contact Lens and Anterior Eye, 37(3), 162-167.
3.Joannes, L., Hough, T., Hutsebaut, X., Dubois, X., Ligot, R., Saoul, B., ... & De Coninck, K. (2010). The reproducibility of a new power mapping instrument based on the phase shifting schlieren method for the measurement of spherical and toric contact lenses. Contact Lens and Anterior Eye, 33(1), 3-8.
Figure 1: Illustration ofMoiré deflectometry technique with two identical gratings and a position-sensitive detector.