Ciliary Muscle & Lens Accommodation

This simulator builds a schematic cross-section of the eye's focusing system — cornea, crystalline lens, ciliary muscle ring and the zonule fibers strung between them — and drives it with the real Helmholtz mechanism: contracting the ciliary muscle slackens the zonules and lets the lens round up, increasing its optical power. An age control applies Duane's classic amplitude-of-accommodation curve, capping how much power the lens can actually gain even when the muscle contracts fully, which is the real mechanical cause of presbyopia. A traced fan of light rays from an adjustable-distance target shows, frame by frame, whether the eye's vergence sum lands the image exactly on the retina or leaves it defocused in front of or behind it.