Module 1: Eye Anatomy

A cutaway picture of the eye

 

 

The eye is an essential organ because it gives us a sense of sight, which is necessary to detect light. Sight not only enables us to appreciate shapes and physical depth, but also to look for food and to detect danger. In this module, the volunteer will learn about the various components that make up this powerful machinery.

1.1 From Light to Sight: How does the Eye Confer Vision?(1)

As the light enters the eye, it passes through the cornea, which bends and focuses the light on the lens.

  1. The pupil controls the amount of light that enters the eye.A picture showing the rods and cones of the retina
  2. The lens then focuses the light onto the retina, forming an inverted image. The lens changes its shape to adjust the focus on both distant and near objects, a process called accommodation.
  3. Photoreceptors on the retina generate electrical signals which are sent to the brain via the optic nerve.
  4. The brain interprets the message, re-inverting the image so that we see an upright image.

1.2 Eye Anatomy

For a cross-sectional diagram of the eye, please visit: http://www.allaboutvision.com/resources/anatomy.htm

The following table shows the basic parts of the eye and their functions:(2)(3)

Part

Function

 

Cornea

A thin, transparent and curved membrane that covers the front part of the eye, protecting the inside of the eye from dust and other matter. It also helps to focus the light onto the retina.

 

Pupil

The little black spot in the center of the iris that controls the amount of light reaching the retina by expanding in the dark to allow more light in, and contracting in the light to prevent excess light from entering.

 

Aqueous humor

A fluid produced by the ciliary body that circulates through the front and rear of the eye to maintain eye pressure and provide nourishment to the cornea and the lens.

Iris

The colored part of the eye that contains very fine muscles that control the size of the pupil.

Conjunctiva

A thin lining over the sclera that produces mucus to lubricate the eye.

Ciliary body

Contains a gland that secretes aqueous humor and a muscle that contracts and expands to control the curvature of the lens.

Lens

Focuses the light onto the retina.

Vitreous body

A clear gel that fills the eye and provides it with a spherical shape.

 

Optic disk

The point where the retina meets the optic nerve, which is often referred to as the blind spot because of its insensitivity to light.

Optic nerve

Made up of a bundle of nerve fibers, the optic nerve delivers electrical impulses from the retina to the brain.

Macula

A tiny part of the retina that focuses and produces color vision.

Retina

A layer of membrane lining the back of the eye which contains the light-sensitive photoreceptor cells

Chloroid

Located between the sclera and the retina, it is made up of blood vessels that provide nourishment to the eye.

Sclera

The outer, white part of the eye that gives protection to the delicate inner structures.

Go To Module 2: Eye Conditions >>

Footnotes

(1) Adapted from Haddrill, Marilyn. "Refraction and Refractive Errors:How the Eye Sees." Allaboutvision. Jun 2006. Access Media Group LLC. 7 Jul 2009 <http://www.allaboutvision.com/eye-exam/refraction.htm>.

(2) Adapted from "FAQ - How does the Human Eye Work?." Pasadena Eye. 7 Jul 2009 <http://www.pasadenaeye.com/faq/faq15/faq15_text.html>.

(3) Adapted from Segre, Liz. "Eye Anatomy Explained - AllAboutVision.com." AllAboutVision. Jul 2008. Access Media Group LLC. 7 Jul 2009 <http://www.allaboutvision.com/resources/anatomy.htm>.