The Human Eye: Structures and Function

Learning Outcomes

• Relate the structures of the sense organs to the type of stimulus they receive.

• Label a diagram of the eye.

• Describe how light travels through the eye and a message is communicated to the brain.

Cornea

• As light enters the eye, it first passes through the cornea.

• The cornea is a clear, convex-shaped covering that protects the front of the eye and helps to focus incoming light.

• The cornea is constantly lubricated by a film of tears.

Aqueous Humor

• After light passes through the cornea, it travels through a clear, watery fluid called the aqueous humor.

• This fluid circulates throughout the front part of the eye, delivering oxygen and nutrients while maintaining a constant pressure inside the eye.

Iris

• The iris is the colored part of the eye, made up of a ring of smooth muscles.

• As light conditions change, the iris may dilate to make the pupil bigger (in dim light) or constrict to make the pupil smaller (in bright light).

• This process controls the amount of light entering the eye.

Pupil

• The pupil is a disc-shaped hole in the center of the iris that allows light to enter the eye.

• The size of the pupil depends on the brightness of the environment; it's larger in dim environments and smaller in bright environments.

Lens

• After light travels through the pupil, it must pass through the lens.

• The lens is responsible for focusing light onto the retina.

• The lens can change its shape using the ciliary muscles to focus on nearby and distant objects through a process called accommodation.

Vitreous Humor

• The eye is filled with a clear, jelly-like substance called the vitreous humor.

• This substance helps the eye maintain its shape and further focuses the light onto the retina.

Retina

• The retina is a thin, light-sensitive tissue lining the back of the eye that receives and processes the light signals.

• For a clear image, light must be properly focused onto the retina, and the surface of the retina must be flat, smooth, and in good working order.

Optic Nerve

• The optic nerve is a bundle of nerve fibers that carries visual information from the eye to the brain.

• The point at which the optic nerve passes through the retina is called the blind spot because there are no photoreceptors there.

Path of Light Through the Eye

• The path of light through the eye:

  • Cornea

  • Aqueous Humor

  • Pupil

  • Lens

  • Vitreous Humor

  • Retina