How do corrective lenses redirect light before it enters the eye?

The eye forms an image on the retina, the light-sensitive tissue at its back. The relationship between the eye’s focusing power and its length matters. If rays come together before or beyond the retinal surface, the light reaching that surface is spread rather than sharply focused.

In the relaxed myopic model shown initially, nearly parallel rays from a distant object meet in front of the retina. A properly chosen diverging eyeglass lens changes the incoming rays before they enter the eye. The combined optical system can then bring them together on the retina instead of too far forward.

Hyperopia has the opposite focusing relation in this simplified model: without suitable compensation, the focus would lie behind the retina. A converging external lens can add the needed convergence. The diagram holds accommodation fixed, so this is not the process of the eye changing its own lens shape to focus at different distances.

A lens is therefore part of a combined system, not a replacement retina or a direct enlargement of the eye. Real correction depends on the individual optical situation, including effects omitted from this schematic. The ray paths explain the direction of compensation without calculating a prescription.