The Eye

Major Parts of the Eye

• Cornea -– clear, transparent portion of the outer coat of

the eyeball through which light passes to the lens.

• Iris -– gives our eyes color

– smooth muscles that open or close an apeture called the PUPIL.

• Pupil - Opening in middle of iris.

• Lens– Eye's primary light-focusing

structure located behind pupil.

– Muscles attach to it that contract causing lens to contract enabling lens to focus light.

•Draw this

Aqueous vs Vitreous Humour

• aqueous is a clear, watery

• anterior and posterior chamber (anterior compartment)

• vitreous is a transparent, colorless mass of soft, gelatinous material

• behind the lens - posterior “compartment”

• Note: your book only mentions anterior compartment (aqueous) and posterior compartment (vitreous)

Eye layers

• Conjunctiva – is a clear membrane covering the white of the

eye (sclera)

• Sclera – is the white of the eye

• Choroid– carries blood vessels, is the inner coat between

the sclera and the retina

Retina

• A thin membrane on back of eye that contains light-sensitive receptors (rods & cones).

• Cones– Light receptors that are sensitive only in

bright light.– They can distinguish form & colour very

well.

• Rods– Light receptors that are sensitive in dim

light.– They cannot distinguish colour &

therefore, you only see shades of gray in dim light.

• Macula – is a small area in the retina that provides our most

central, acute vision.

– Small depressed area in centre of macula directly in line with centre of cornea & lens is called the FOVEA.

•Fovea is the region of keenest vision.

•Light-sensitive cones are concentrated in fovea.

• Optic Nerve

– Carries nerve impulses to the brain created when light strikes rods & cones.

Blind spot• the point on the retina where the

approximately 1 million axons converge on the optic nerve, there are no rods or cones. This spot, called the blind spot, is thus insensitive to light.

Eye Muscles

• Movement of the eye is controlled by six muscles:

• Medial rectus- lies on the inner side

• Lateral rectus- lies on the outer side

• Superior rectus- lies above the eye

• Inferior rectus- lies below the eye

• Superior oblique- lies above and runs obliquely

• inferior oblique- lies below and runs obliquely

Why do we see?

– Light reflected from object enters your eye.

– Cornea & lens bend light rays together.– Rays cross & focus on retina which

appears upside down & backward.– Light strikes rods & cones creates

nerve impulses that are carried by optic nerve to brain to be interpreted.

– Retinal image reversed in brain so we see object right side up.

Retinal Layers

• Composed of three layers:

– 1. Ganglion cell layer– 2. Bipolar cell layer– 3. Rod and cone cell layer

• rods and cones - actual photoreceptors

• ganglion cells - transmit to the brain; the axons of these ganglion cells make up the optic nerve.

• bipolar cells - process input from photoreceptors and transmit the signal to ganglion cells.