Eye Refraction Lab: Exact Ray-Traced Schematic Eye (2D)

This 2D companion to the 3D reduced-eye model traces real light rays, one Snell's-law refraction at a time, through the eye's three actual optical surfaces — the cornea and both faces of the crystalline lens — instead of combining everything into a single dioptric power. Because individual rays across the pupil are followed independently, the simulator reveals two effects the single-power model cannot: real spherical aberration (marginal and paraxial rays focusing at slightly different points) and an actual retinal blur-spot diameter computed from where the traced ray bundle lands relative to the retina. Move the axial-length slider to turn an emmetropic eye into a myopic or hyperopic one exactly as happens physiologically, use accommodation to watch the ciliary muscle's lens-curvature change pull the focus forward, and turn on the corrective lens to see a real spectacle prescription — including the vertex-distance effect of the lens sitting 12 mm in front of the eye — bring the traced rays back onto the retina.