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Yuki Shitanoki, Yasuhiro Koike, Akihiro Tagaya; Reduction of astigmatism in progressive addition lenses by employment of graded-index materials. Journal of Vision 2008;8(17):83. doi: https://doi.org/10.1167/8.17.83.
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Graded-index (GRIN) progressive addition lens (PAL) was successfully fabricated, and GRIN's potential for reduction of astigmatism in PAL was confirmed. Progressive-addition lens (PAL) is an ophthalmic lens for presbyopia, and a multifocal lens that permits distant, intermediate and near vision without any discontinuity in the transition zone. However, rotationally asymmetric surface geometry of PALs causes localized astigmatism that degrades wearer's vision. Astigmatism is caused by the difference of light focusing power around considering points in a lens. On the other hand, graded-index (GRIN) which represents gradual change of refractive index in a material can add or reduce light focusing power of the material in the direction of refractive index change. In this research, reduction of astigmatism in PAL was demonstrated by applying GRIN to the axis with smallest light focusing power.
GRIN material was prepared by the diffusion of methyl methacrylate (MMA (nd at polymer = 1.492)) or 2,2,2-trifluoroethyl methacrylate (3FMA (nd at polymer = 1.421)) monomer from a portion of periphery into cross-linked benzyl methacrylate (BzMA (nd at polymer=1.568)) flat gel. BzMA flat gel was prepared by UV polymerization of BzMA, cross-linking agent ethylene glycol dimethacrylate (EDMA) and photopolymerization initiator DAROCURE 1173. The obtained GRIN material was attached to a mold of commercially available PAL and polymerized by UV. As a result, reduction of astigmatism was confirmed locally in the fabricated PAL and GRIN-PAL using lens meter.
In conclusion, GRIN-PAL was successfully fabricated and the validity of GRIN employment for the astigmatism reduction in PAL was demonstrated experimentally.
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