Accommodation Demand Map: Presbyopia in 2D Phase Space

This is the 2D companion to the 3D ciliary-muscle-and-lens simulator, built on the exact same Helmholtz vergence optics and Duane's amplitude-of-accommodation curve, but represented as two flat phase-space diagrams instead of a rendered eyeball. On the left, Duane's curve plots the age-dependent ceiling on optical power directly against age — the real mechanical cause of presbyopia. On the right, a live-scanned 2D field maps every combination of ciliary contraction and target distance to its resulting defocus, so the shrinking "sharp focus" region as age increases becomes something you watch happen to the parameter space itself, rather than to a 3D lens shape.