Human Eye - Structure of the Eyeball

The tough, white outer layer of the eyeball made of fibrous tissue, visible as the white part of the eye.

The transparent, bulged-out front part of the sclera that covers the coloured part of the eye and allows light to enter.

The middle, dark-pigmented layer of the eye rich in blood vessels; it nourishes the eye and prevents light scattering.

A muscular part of the choroid layer that changes the shape of the lens to focus light on the retina.

The coloured part of the eye (extension of choroid) that controls the size of the pupil using circular and radial muscles.

The circular opening in the centre of the iris that regulates the amount of light entering the eye.

The innermost light-sensitive layer of the eye containing rod and cone cells that detect light and colour.

Light-sensitive cells in the retina that work in dim light and contain the pigment rhodopsin; they do not detect colour.

Light-sensitive cells in the retina responsible for colour vision and bright light, containing the pigment iodopsin.

• The eyeball has three layers: outer sclera (protective), middle choroid (vascular and pigmented), and inner retina (sensory layer).
• The sclera is tough and white, giving shape to the eye; its front transparent part forms the cornea, which helps in focusing light.
• The choroid contains blood vessels and pigment, nourishes the eye, and prevents internal reflection; it forms the ciliary body and iris.
• The iris controls the size of the pupil to regulate light entry; the pupil dilates in dim light and constricts in bright light.
• The lens, along with the cornea, focuses light onto the retina to form a clear image.
• The retina contains rod cells (for dim light) and cone cells (for bright light and colour); the fovea provides sharp vision, while the blind spot lacks photoreceptors.
• Light stimulates rods and cones, generating nerve impulses that pass through bipolar and ganglion cells to the optic nerve, which carries them to the brain for image perception.