Simulation of commercial vs theoretically optimised contact lenses for presbyopia.

PURPOSE: To compare theoretically optimised bifocal contact lens optical designs to commercially available optical designs for presbyopia.

METHODS

Retinal images were simulated, using a numerical eye model, from -6 (i.e., near vision) to +2 D for each 0.25 D. Ten optical profiles were simulated. Four of them corresponded to commercial contact lenses (i.e., Acuvue Oasys for Presbyopia®, Air Optix Aqua Multifocal®, Purevision Multifocal® and Distance Biofinity Multifocal®). We also included six optimised profiles: (1) a combination of primary and secondary spherical aberration, (2) bifocal profiles with 2, 5 and 8 concentric zones, and (3) a combination of spherical aberrations with the 5 and 8 zones profiles. Twenty subjects scored the quality of vision of calculated images (i.e., three high-contrast 0.40 logMAR letters) for each design and vergence with a five-item continuous grading scale. They viewed these images through their best sphero-cylindrical correction and a 3-mm pupil to limit the impact of their aberrations. To quantify the ability of a bifocal optic to maintain a certain level of quality of vision, we calculated two criteria: (1) the area under the through-focus quality of vision curve higher than 2 (i.e., limit between poor and fair quality of vision) normalised by the same area calculated on the naked eye's curve, and (2) the width of the curve at a level of 2 (i.e., depth-of-focus).

RESULTS

Commercial contact lens profiles did not give an image quality and depth-of-focus as good as the theoretically optimised optical profiles. Based on these two criteria, the best bifocal profiles were those with 5 and 8 concentric zones. Important inter-individual variations were observed for all profiles. We also observed that some subjects did not obtain any benefit with all the designs whereas others seemed to be satisfied whatever the optical profiles.

CONCLUSION

Our previously optimised designs with 5 and 8 zones gave the best benefit and depth-of-focus. As their image quality is better than commercially available designs, it would be interesting to prototype these designs and to test them in a clinical setting.