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Vision and the Human Eye

Eyes with normal vision see images images clearly at near distances.

The anatomy of the normal human eye, seen from the side, is shown in the figure below.
The foremost part of the eye is transparent and called the cornea. The colored iris with the pupil in the center lies behind the cornea. Deeper still is the lens, while the light sensitive tissue of the retina lines the inner surface of the eye.

Good vision has its origin in the accurate focusing of sharp images on the retina of the eye.

For normal vision, the optical system of the eye refracts light rays (images we see) so they are focused on the retina, typically in the fovea (macula), the area of highest resolution.

Normalsichtiges Auge: Der Brennpunkt liegt auf der Netzhaut

If one or more components of the eye are not precisely in tune, light rays are not focused on the retina, but rather in front or behind it, causing blurry images of the environment.
This condition is referred to as refractive error, which is a collective term for nearsightedness (myopia), farsightedness (hyperopia) and astigmatism.