The eye

The model eye is drawn about 15 times bigger than a real eye, which is about 2.4 cm across. The rays are drawn by a simple rule: the cornea bends every ray by the same amount, and the lens bends it the rest of the way, more when it is fatter. No distances or focal lengths are worked out.

The lamp settings 1 to 5 are marks on the lamp’s dial, not measured brightness. The pupil diameters (7.5, 6.0, 4.5, 3.5, 3.0 mm) are typical values for a person, not measurements of your own eye.

In a real eye the lens changes shape by itself. The control on the model’s stand is only there so that you can see what the change does.

The magnifier on the retina draws far fewer rods and cones than there really are. The faded colours in dim light are a simulated view, not a photograph.

The glow along the optic nerve is a convention that shows where the impulses are: a real impulse gives out no light.

With reduced motion each process is shown at its start and its end, and the lamp and the lens change at once.