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Top - variation in the average and equivalent refractive indices of a lens with the gradient of refractive index given by Eq. (1) as a function of the lens parameter p describing the index gradient: surface and central refractive indices are 1.37 and 1.415, respectively, and other details relevant to equivalent index are as in Table 1. Bottom - variation in the refractive error of the eye model given in Table 1 when the lens parameter p is changed.
