Eye

The eye is a sensory organ that detects light and enables vision. It is part of the visual system and works with the brain to interpret images. The eye has three main layers: the sclera, a tough outer coat; the uvea, the vascular middle layer; and the retina, the light-sensitive inner layer. At the front, the cornea is transparent and helps focus light. Behind it lies the aqueous humor, the lens, and the vitreous body that fills most of the eye. The pupil, a variable opening in the iris, admits light, which the iris regulates.

The cornea and lens refract light to form a focused image on the retina. The lens changes shape through accommodation to focus objects at different distances. The retina contains photoreceptors: rods, which are sensitive to light and motion, and cones, which detect color and detail. Signals from photoreceptors are conveyed through neurons to the retina’s output layer, then via the optic nerve to the brain.

The retina has a specialized region called the fovea, responsible for sharp central vision, while the periphery provides motion detection and broader field. The optic nerve carries signals to the brain where they are processed in the visual cortex. Some fibers cross at the optic chiasm, enabling binocular depth perception.

Common refractive and eye diseases include myopia (nearsightedness), hyperopia (farsightedness), and astigmatism, usually corrected with glasses, contact lenses, or refractive surgery. Cataracts cloud the lens, glaucoma damages the optic nerve often from elevated pressure, and macular degeneration affects central vision. Color vision deficiencies are typically genetic.

Eye health is supported by protection from ultraviolet light, a balanced diet, and regular eye examinations. Blinking and tear film keep the surface moist and clear. Systemic conditions such as diabetes and hypertension can affect eye health and vision.