vision

Vision is the sense by which organisms perceive their surroundings through light. In humans, the visual system translates light into neural signals that the brain can interpret, enabling perception of shapes, color, depth, and motion and guiding behavior.

The eye collects and focuses light using the cornea and lens. Light is projected onto the retina, where photoreceptors—rods sensitive to dim light and peripheral vision, and cones handling color and acuity—convert photons into electrical signals. These signals pass through bipolar and ganglion cells to the optic nerve. The nerves partially cross at the optic chiasm, relaying information to the thalamus and then to the primary visual cortex in the back of the brain.

Neural processing divides into two main streams: the dorsal stream, which analyzes motion, spatial location, and action (the “where/how” pathway), and the ventral stream, which identifies objects and color (the “what” pathway). Interaction of these streams supports depth perception, contour interpretation, and scene understanding.

Vision develops from infancy, with improvements in acuity, color discrimination, and depth perception continuing into childhood. Clinically, vision is evaluated with acuity tests (for example, the Snellen chart), visual fields testing, and imaging techniques such as optical coherence tomography.

Common vision problems include refractive errors (myopia, hyperopia, astigmatism), cataracts, glaucoma, age-related macular degeneration, and diabetic retinopathy. Treatments range from corrective lenses and contact lenses to refractive surgery and medical or surgical management of diseases. Assistive devices and rehabilitative services support people with vision impairment.