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Impact of contact lens zone geometry and ocular optics on bifocal retinal image quality
Author(s) -
Bradley Arthur,
Nam Jayoung,
Xu Renfeng,
Harman Leslie,
Thibos Larry
Publication year - 2014
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.12110
Subject(s) - optics , spherical aberration , wavefront , entrance pupil , concentric , diffraction , image quality , depth of focus (tectonics) , geometry , pupil , lens (geology) , physics , mathematics , geology , image (mathematics) , computer science , computer vision , paleontology , subduction , tectonics
Purpose To examine the separate and combined influences of zone geometry, pupil size, diffraction, apodisation and spherical aberration on the optical performance of concentric zonal bifocals. Methods Zonal bifocal pupil functions representing eye + ophthalmic correction were defined by interleaving wavefronts from separate optical zones of the bifocal. A two‐zone design (a central circular inner zone surrounded by an annular outer‐zone which is bounded by the pupil) and a five‐zone design (a central small circular zone surrounded by four concentric annuli) were configured with programmable zone geometry, wavefront phase and pupil transmission characteristics. Using computational methods, we examined the effects of diffraction, Stiles Crawford apodisation, pupil size and spherical aberration on optical transfer functions for different target distances. Results Apodisation alters the relative weighting of each zone, and thus the balance of near and distance optical quality. When spherical aberration is included, the effective distance correction, add power and image quality depend on zone‐geometry and Stiles Crawford Effect apodisation. When the outer zone width is narrow, diffraction limits the available image contrast when focused, but as pupil dilates and outer zone width increases, aberrations will limit the best achievable image quality. With two‐zone designs, balancing near and distance image quality is not achieved with equal area inner and outer zones. With significant levels of spherical aberration, multi‐zone designs effectively become multifocals. Conclusion Wave optics and pupil varying ocular optics significantly affect the imaging capabilities of different optical zones of concentric bifocals. With two‐zone bifocal designs, diffraction, pupil apodisation spherical aberration, and zone size influence both the effective add power and the pupil size required to balance near and distance image quality. Five‐zone bifocal designs achieve a high degree of pupil size independence, and thus will provide more consistent performance as pupil size varies with light level and convergence amplitude.