Anatomy of The Eye

The anatomy and physiology of the human eye is an important part of many courses e.g. in biology, human biology, physics, and practical courses in medicine, nursing, and therapies.

This simple introduction the subjects of 'the eye' and 'visual optics' includes a simple diagram of the eye together with definitions of the parts of the eye labelled in the illustration.

Ciliary Muscle Iris Hyaloid Membrane Hyaloid Membrane Vitreous Humour Sclera Geometrical Axis Optic Nerve Ciliary Muscle Hyaloid Membrane Vitreous Humour Fovea Visual Axis Geometrical Axis Lens Geometrical Axis Lens Cornea Aqueous Humour Aqueous Humour Retina Choroid Optic Nerve Retina Choroid

Above: Schematic diagram of the Structure of the Human Eye.



Definition / Description

Aqueous Humour

The aqueous humour is a jelly-like substance located in the anterior chamber of the eye.


The choroid layer is located behind the retina and absorbs unused radiation.

Ciliary Muscle

The ciliary muscle is a ring-shaped muscle attached to the iris.

It is important because contraction and relaxation of the ciliary muscle controls the shape of the lens.


The cornea is a strong clear bulge located at the front of the eye (where it replaces the sclera - that forms the outside surface of the rest of the eye).

The front surface of the adult cornea has a radius of approximately 8mm.

The cornea contributes to the image-forming process by refracting light entering the eye.


The fovea is a small depression (approx. 1.5 mm in diameter) in the retina.

This is the part of the retina in which high-resolution vision of fine detail is possible.


The hyaloid diaphragm divides the aqueous humour from the vitreous humour.


The iris is a diaphragm of variable size whose function is to adjust the size of the pupil to regulate the amount of light admitted into the eye.

The iris is the coloured part of the eye (illustrated in blue above but in nature may be any of many shades of blue, green, brown, hazel, or grey).


The lens of the eye is a flexible unit that consists of layers of tissue enclosed in a tough capsule. It is suspended from the ciliary muscles by the zonule fibers.

Optic Nerve

The optic nerve is the second cranial nerve and is responsible for vision.

Each nerve contains approx. one million fibres transmitting information from the rod and cone cells of the retina.


The papilla is also known as the "blind spot" and is located at the position from which the optic nerve leaves the retina.


The pupil is the aperture through which light - and hence the images we "see" and "perceive" - enters the eye. This is formed by the iris. As the size of the iris increases (or decreases) the size of the pupil decreases (or increases) correspondingly.


The retina may be described as the "screen" on which an image is formed by light that has passed into the eye via the cornea, aqueous humour, pupil, lens, then the hyaloid and finally the vitreous humour before reaching the retina.

The retina contains photosensitive elements (called rods and cones) that convert the light they detect into nerve impulses that are then sent onto the brain along the optic nerve.


The sclera is a tough white sheath around the outside of the eye-ball.
This is the part of the eye that is referred to by the colloquial terms "white of the eye".

Visual Axis

A simple definition of the "visual axis" is "a straight line that passes through both the centre of the pupil and the centre of the fovea". However, there is also a stricter definition (in terms of nodal points) which is important for specialists in optics and related subjects.

Vitreous Humour

The vitreous humour (also known as the "vitreous body") is a jelly-like substance.


The zonules (or "zonule fibers") attach the lens to the ciliary muscles.

To learn more about the eye and how it works it is useful to understand some simple but important aspects of light.

Next: Understanding Light (to explain how the eye works).

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