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Lenticular plots showing iso-indicial contours for young (a) and old (b). Negative m shows a bunching of contours towards the equator (c), a behaviour seen in recent studies [4, 12]. The three lenses have the same external geometry and parameter P representative of a 30 year old, after [5, 21, 22]: Ra = 11.2 mm, Rp = 6.0 mm, Ka = −4.5, Kp = −1.1, lens thickness T = 3.6 mm, P = 3, nc = 1.415 and ns = 1.37.
