Physics of the eye

The eye and lenses

The eye focuses light on the retina mainly with the cornea, fine-tuned by the lens. Lenses obey $\frac1f=\frac1u+\frac1v$ and have power $P=\frac1f$ in dioptres (D). A normal eye sees from $25$ cm (near point) to infinity (far point). Short sight (myopia) is corrected with a diverging lens; long sight (hypermetropia) with a converging lens; astigmatism with a cylindrical lens.