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Multifocal contact lenses: towards customisation?
Author(s) -
FariaRibeiro Miguel,
GonzálezMéijome José M
Publication year - 2019
Publication title -
ophthalmic and physiological optics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.147
H-Index - 66
eISSN - 1475-1313
pISSN - 0275-5408
DOI - 10.1111/opo.12597
Subject(s) - strehl ratio , zernike polynomials , wavefront , spherical aberration , optics , contact lens , lens (geology) , mathematics , reduction (mathematics) , power (physics) , metric (unit) , depth of focus (tectonics) , physics , geometry , geology , engineering , paleontology , operations management , subduction , quantum mechanics , tectonics
Purpose Firstly, to determine if eyes with spherical aberration ( SA ) that deviates significantly from the average level underperform when fitted with a simultaneous‐imaging contact lens ( CL ) with a power profile calculated for an ‘average eye’. Secondly, to determine if CL customisation can improve image quality in these eyes after fitting with a bifocal CL . Methods A statistical model of the wavefront aberration function of normal eyes was used to generate a vector of Zernike fourth‐order SA coefficients from 100 synthetic eyes. Four bifocal power profiles were modelled: centre‐near ( CN ) or centre‐distance ( CD ), and two‐zone or four‐zone. All designs had 0.1‐mm‐wide transition zones. Different levels of distance and add powers were modelled, using well‐established computational wave‐optics methods. Zone widths were optimised to obtain maximal multifocal efficiency ( MFE ), a metric based on the visual Strehl that synthesises the through‐focus curve in one number. The MFE was calculated for each synthetic eye coupled with each bifocal power profile. Results For an ‘average eye’, the mean MFE values were 0.33 vs 0.25 and 0.32 vs 0.29, for CN vs CD and two vs four zone designs, respectively. When the four power profiles were assessed in eyes with non‐average levels of ocular SA , the MFE decreased with higher levels of SA (eye and CL combined) for all designs. Some of this reduction in MFE could be prevented by adjusting the nominal distance and add power of the bifocal profiles to compensate for the increased or decreased level of combined SA . The four‐zone CN profile showed better tolerance for different levels of ocular SA than the two‐zone designs, but this was not true for the four‐zone CD design. Conclusion Eyes with SA levels differing significantly from the average level underperform when fitted with simultaneous‐imaging CL s with power profiles calculated for average eyes. Our findings suggest that visual performance at distance and near when wearing bifocal CL s can be improved by using a semi‐customised approach.