Sehsystem

Sehsystem, or the visual system, is the biological mechanism responsible for sight in humans and many animals. It combines the eye as the sensory organ with neural pathways that convert light into perception. The system begins with the retina, a layered neural tissue at the back of the eye that contains photoreceptors and interneurons that transform light into electrical signals. Photoreceptors—rods and cones—provide the first transduction: rods support vision in low light, cones support daylight vision and color discrimination. Signals pass through bipolar and ganglion cells; the axons of ganglion cells form the optic nerve.

At the optic chiasm, nasal retinal fibers cross to the opposite hemisphere, while temporal fibers remain on the same side, creating a contralateral representation of the visual field. The optic tract relays information to the lateral geniculate nucleus of the thalamus, and from there to the primary visual cortex (V1) in the occipital lobe via the optic radiations. The retina and cortex preserve retinotopy, enabling spatial mapping and feature extraction.

Beyond V1, information proceeds along two major processing streams: the dorsal stream, associated with spatial location and motion, and the ventral stream, associated with object identity and color. Additional pathways contribute to eye movements and reflexive orienting via the superior colliculus. Color vision arises from three cone types and opponent-process signaling.

Clinical relevance and development: abnormalities at any level—from refractive errors and cataracts to glaucoma, macular degeneration, or cortical lesions—can impair vision. The Sehsystem develops through infancy with periods of neural plasticity that influence visual acuity and perception. Assessment typically combines acuity tests, field exams, and imaging of retinal and cortical pathways.