seeing

Seeing is the sense of visual perception, the process by which the brain interprets light patterns detected by the eyes to form images and guide behavior. It relies on light entering the eye, being focused, and being converted into neural signals for processing in the brain.

The eye collecting light begins with the cornea and lens focusing it onto the retina, a light-sensitive layer containing photoreceptors called rods and cones. Rods mediate light sensitivity and motion detection; cones support color vision and high-acuity vision. Signals from photoreceptors pass to retinal neurons, then through the optic nerve. At the optic chiasm, some nerve fibers cross to the opposite hemisphere, and signals travel via the thalamus to the primary visual cortex in the occipital lobe. Visual information is processed along multiple pathways, including the ventral stream for object identity and the dorsal stream for spatial location and movement. The brain integrates context, memory, and attention to form perception.

Visual ability varies with development and experience. Binocular vision enables depth perception through stereopsis; color vision depends on cone types. Accommodation and pupil adjustment regulate focus and brightness. Aging and disease can affect vision.

Common vision problems include refractive errors such as myopia, hyperopia, astigmatism, and presbyopia; cataracts, glaucoma, age-related macular degeneration, diabetic retinopathy, and amblyopia. Treatments range from corrective lenses and vision aids to surgery and therapy. People may also rely on assistive devices and environmental adaptations to improve sight.