EYE STRUCTURE and VISION GENERAL FACTS ABOUT THE

EYE STRUCTURE and VISION

GENERAL FACTS ABOUT THE EYE Is a sphere about 1 inch in diameter (about 2. 5 cm. ) Is protected by the orbital socket of the skull and by the eyebrows, eyelids, and eyelashes. Bathed in fluid secreted by the lacrimal glands (tears empty into nasal cavity. ) Thin membrane which lines the eyelids and covers part of the eye is called the conjunctiva. It secretes mucous to help lubricate the eye.

3 Layers of the Eye • Sclera • Choroid coat • Retina

Wall of the eye is made up of 3 layers or coats. • Sclera - – Outer layer – “white of the eye” – tough, fibrous capsule which maintains the eye’s shape – Extrinsic Muscles muscles that are attached to the sclera and responsible for moving the eye.

Cornea - “Window of the Eye” • Located in front center of the sclera • Transparent - no blood vessels • Allows outside light to pass through the eye. • Gets oxygen and nutrients through lymph fluid.

Choroid Coat - Middle Layer of the Eye • Contains many blood vessels that provides nourishment to the eye. • Pupil - dark circular opening in the center • Iris - Colored muscular layer surrounding pupil • Intrinsic Muscles –change size of iris to control amount of light entering through the pupil.

• Crystalline structure located behind the iris and pupil • Sittuated between the anterior and posterior chambers • Elastic, disc-shaped biconvex LENS

Chambers of Fluid Within the Eye (help to maintain the eyeball’s spherical shape • Anterior Chamber – Filled with a clear watery fluid called aqueous humor. – Found in front of the lens • Posterior Chamber – Filled with a clear, jelly -like fluid called vitreous humor. – Found in back of lens.

Retina - Innermost Layer • Located between the posterior chamber and the choroid coat. • Light rays focus an image on the retina • The image travels to the cerebral cortex via the OPTIC NERVE • If light rays do not focus properly on the retina, corrective lenses can bend light rays to correct vision • Contains rods and cones.

RODS AND CONES – Rods – sensitive to dim light for night vision Cones – Sensitive to bright light and color

OPTIC DISC • Area on retina known as the “blind spot” • Where nerve fibers gather to form optic disc • No rods or cones

Pathway of Vision Cornea Pupil Lens (Where light rays are refracted) Rods and Cones (pick up stimulus) Retina Optic Nerve

Lights out folks!