human eye

Introduction
Anatomy of the visual apparatus
- Structures auxiliary to the eye
  - The orbit
  - The eyelids
    - The conjunctiva
    - The fibrous layer
    - The muscles of the lids
    - The skin
  - The glandular apparatus
  - Extraocular muscles
- The eye
  - General description
  - Outer and middle tunics of the globe
    - The outermost coat
    - The uvea
  - The inner tunic of the globe
    - The epithelia
    - The retina
  - The transparent media
    - The aqueous humour
    - The vitreous body
    - The crystalline lens
The visual process
- The work of the auxiliary structures
  - The protective mechanisms
    - Innervation
    - Blink reflexes
    - Normal rhythm
    - Secretion of tears
  - Movements of the eyes
    - The axes of the eye
    - Actions of muscles
    - Binocular movements
    - Nervous control
    - Reflex pathways
    - Voluntary centre
    - The nature of eye movements
    - Vision suppression during a saccade
- The work of the optical lens system
  - Refraction by cornea and lens
  - Normal sightedness and near- and farsightedness
  - Accommodation
    - Effects of accommodation
    - Mechanism of accommodation
    - Nerve action
  - The pupil
  - The near response
The work of the retina
- Some basic facts of vision
  - Measurement of the threshold
  - Scotopic sensitivity curve
  - Loss of dark adaptation
  - Bleaching of rhodopsin
- Synaptic organization of the retina
  - Plexiform layers
  - Convergence of the messages
- Absolute threshold and minimum stimulus for vision
  - Quantum fluctuations
  - Spatial summation
  - Temporal summation
- Inhibition
- Flicker
- Visual acuity
  - Measurement
  - Anatomical basis: the retinal mosaic
  - The retinal image
- Electrophysiology of the retina
  - Neurological basis
  - Anatomical basis
  - Direction-sensitive ganglion cells
  - The electroretinogram
  - Flicker
  - Visual acuity
- Colour vision
  - Spectral sensitivity curve
  - Colour mixing
  - Colour defectiveness
  - Responses of uniform population of photoreceptors
  - Young-Helmholtz theory
  - The nervous messages
  - Lateral geniculate cells
- The photochemical process
  - Rhodopsin
  - The transduction process
  - Cone pigments
The higher visual centres
- The visual pathway
  - Fusion of retinal images
  - The visual field
  - Lateral geniculate body
  - Striate area
  - Pupillary pathways
  - Point-to-point representation
  - Visuopsychic or circumstriate areas
- Integration of the retinal halves
  - Corpus callosum
  - Stereopsis in the midline
  - Callosal transfer
  - Superior colliculi
Some perceptual aspects of vision
- Projection of the retina
  - Relative positions of objects
  - Position in relation to observer
- Visual estimates
  - The directions of lines
  - Comparison of lengths
  - Optical illusions
- The perception of depth
  - Monocular cues
  - Binocular vision
- Retinal rivalry
  - Ocular dominance
  - Binocular brightness sensation
Electrophysiology of the visual centres
- Ganglion cells
- Geniculate neurons
- Cortical neurons
  - Eye dominance
  - Cortical architecture
  - Complex neurons
- Stereoscopic vision

References & Edit History Quick Facts & Related Topics

Images, Videos & Interactives

Diagram of a horizontal section of the human eye showing labeled parts including the cornea, iris, lens, retina, sclera, optic nerve, and blood vessels, with internal structures and muscles visible.

Human body systems interactive

Diagram of a horizontal section of the human eye showing labeled anatomical structures, including the cornea, lens, iris, retina, optic nerve, vitreous body, and supporting tissues.

Diagram showing the layered structure of the human retina, with labeled optic nerve fibers, ganglion cells, bipolar neurons, rod cells, cone cells, and pigmented epithelium at the base.

An anatomical illustration of the right eye shows the eyeball and surrounding bones with labeled muscles, including the superior, inferior, medial, and lateral rectus, superior and inferior oblique, levator palpebrae superioris, and the trochlea.

Side-by-side diagrams compare a nearsighted eye, where light focuses in front of the retina, with a normal eye, where light focuses on the retina. Both eyes are labeled with cornea, lens, retina, and sclera.

Side-by-side diagram comparing a farsighted (hyperopic) eye and a normal eye, showing how light focuses behind the retina in hyperopia and directly on the retina in a normal eye, with labeled parts including lens, cornea, sclera, and retina.

Diagram showing how visual information from an object enters the left and right eyes, travels along the optic nerves, crosses at the optic chiasma, and reaches the occipital lobes in the brain for image processing.

A circular perimeter chart for the right eye shows the normal visual field outlined in red, with degrees of arc labeled around the outer edge for measuring visual range.

At a Glance

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human eye summary

Diagram of a horizontal section of the human eye showing labeled parts including the cornea, iris, lens, retina, sclera, optic nerve, and blood vessels, with internal structures and muscles visible. — cross section of the human eye A horizontal cross section of the human eye, showing the major parts of the eye, including the protective covering of the cornea over the front of the eye.

human eye

anatomy

Written by

Hugh DavsonAll

Fact-checked by

Britannica Editors

Last updated

Oct. 28, 2026 •History

human eye, in humans, specialized sense organ capable of receiving visual images, which are then carried to the brain. The eye is protected from mechanical injury by being enclosed in a socket, or orbit, which is made up of portions of several of the bones of the skull to form a four-sided pyramid, the apex of which points back into the head. Thus, the floor of the orbit is made up of parts of the...

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