öga

Öga is the organ of sight in humans and many other animals. It detects light and forms images, enabling vision and spatial orientation. In Swedish, öga is singular for one eye, and ögon is the plural. The term is used in medical, educational, and everyday language.

Anatomy and function: The eye comprises an optical portion that focuses light and a neural portion that processes visual information. The cornea and lens bend light to project an image onto the retina, which lines the back of the eye. The iris controls the size of the pupil, regulating how much light enters. The sclera forms the white outer layer, while the choroid supplies blood to the eye. The retina contains photoreceptor cells: rods, which are sensitive to light and provide peripheral and low-light vision, and cones, which enable color and detailed vision. Signals from the retina travel via the optic nerve to the brain’s visual cortex, where they are interpreted as images.

Development and variation: The eye develops during embryogenesis and matures after birth. Accommodation adjusts focus through the ciliary muscles. Vision varies among individuals, including differences in color vision and acuity. Age-related changes can include presbyopia, cataracts, and macular degeneration.

Clinical notes: Refractive errors such as myopia, hyperopia, and astigmatism are common and typically corrected with lenses. The eye can be affected by diseases such as glaucoma, retinal detachment, diabetic retinopathy, and other conditions requiring medical evaluation and treatment.

Evolution: Eyes have evolved in diverse forms across animal lineages, with vertebrate eyes commonly evolving a camera-type structure that focuses light onto a retina.