Sight

Sight, or vision, is the sense by which living beings perceive light, objects, and space. In humans it involves the eyes as optical organs, the neural retina as the light-sensitive layer, and the brain’s visual cortex as the site of interpretation.

Anatomy: The eye consists of the cornea, iris, pupil, lens, and retina. Light enters through the cornea, passes through the pupil and lens, and is focused on the retina. The retina contains photoreceptors: rods, which function in dim light and detect movement, and cones, which provide color and high-acuity vision. The central retina includes the fovea, where acuity is highest. Signals from photoreceptors are relayed by retinal ganglion cells to the optic nerve.

Processing: The optic nerves from both eyes meet at the optic chiasm, where some nerve fibers cross to the opposite side. Signals then travel to the thalamus (lateral geniculate nucleus) and onward to the primary visual cortex in the occipital lobe. Further processing in association areas enables the perception of form, color, depth, and motion.

Function and variation: Sight allows basic environmental awareness, reading, and facial recognition. Visual acuity, color perception, and depth perception vary among individuals. Common conditions include refractive errors (myopia, hyperopia, astigmatism), cataracts, glaucoma, and age-related macular degeneration. Temporary impairment can arise from injury or diseases affecting the eye or the visual pathways.

Development and protection: Vision develops after birth and improves through childhood. Protective measures include eye hygiene, UV protection, and safety eyewear to prevent injury.