Näköaistiin

Näköaistiin, or the sense of sight, refers to the sensory modality by which organisms detect and interpret light to form visual experiences. In humans and many animals, vision arises from the eye and brain working together to convert light into neural signals and to interpret patterns, colors, movement, and depth.

Anatomy and physiology. Light enters the eye through the cornea and is focused by the lens, with the pupil regulating how much light passes in. The retina, at the back of the eye, contains photoreceptor cells: rods, which are highly sensitive in low light but do not detect color, and cones, which mediate color vision and high spatial acuity. Photopigments in these cells convert light into electrical signals that travel via retinal ganglion cells and the optic nerve. The signals partially cross at the optic chiasm and are relayed to the lateral geniculate nucleus of the thalamus, then to the primary visual cortex in the occipital lobe. From there, higher-level processing splits into the dorsal stream (spatial location and movement) and the ventral stream (object recognition and color). Other pathways, such as the superior colliculus, contribute to reflexive eye movements and orientation.

Development and variation. The visual system develops after birth, with critical periods for normal maturation of acuity and depth perception. Visual experience shapes neural wiring, and deprivation can lead to lasting deficits. Across species, eye structure and visual capabilities vary widely, reflecting ecological needs such as acuity, motion detection, or color discrimination.

Clinical relevance. Common conditions affecting näköaistiin include refractive errors (myopia, hyperopia, astigmatism), cataracts, glaucoma, age-related macular degeneration, and amblyopia. Evaluation typically involves visual acuity testing, refraction, and sometimes perimetry or imaging to assess retinal and optic nerve health.