Vision

Vision is the process by which the eye detects information about the surroundings. Light from objects either emitted or reflected reaches the eye and forms an image on the retina. Specialized light-sensitive cells there convert light into electrical signals that are sent to the brain.

Vision is not simply the capture of light. The brain analyzes these signals and constructs a perception with form, color, distance, and motion. For this reason, scientists divide vision into two fields: the optical part of the eye and its sensory function, and the part of the brain responsible for interpreting the signals.

Structure of the eye

Light first passes through the cornea at the front of the eye, then enters the pupil. The lens inside the eye focuses light onto the retina. Muscles surrounding the lens change its shape so that both nearby and distant objects can be seen—a process called accommodation.

Light-sensitive cells

The retina contains two types of light-sensitive cells: rods and cones. Rods function in dim light but do not distinguish color well. Cones require more light and are responsible for color vision and fine detail. The fovea, the central region of the retina, is densely packed with cones and is the area of sharpest vision.

The pathway to the brain

Signals from the retina travel along the optic nerve. The optic nerves from both eyes meet at the optic chiasm, then proceed to lower brain regions and finally to the visual cortex at the back of the brain. There, recognition of shapes, faces, and movement takes place.

Common conditions

The most frequent problems are myopia and hyperopia, which occur when the image focuses at the wrong point on the retina. Astigmatism also occurs, as do age-related conditions such as cataracts. The cornea, lens, and fluid of the eye can usually be corrected by ordinary means.