senses vision. v i s i o n 70% of all receptors in the body are in the eye

Senses

Vision

V I S I O NV I S I O N

•70% of all receptors in the body are in the eye

External Anatomy

• Eyelids• Eyelashes• Conjunctiva• Lacrimal

glands

Conjunctiva

• Inner surface of eyelid

Infection: Conjunctivitis

• “Pink eye”

Lacrimal Glands

• Lubricate the eye

• Lysozymes – natural antibiotic

• Drains into nose

Eye Movement•6 muscles / eye• 3 Cranial nerves

– III Oculomotor – IV Trochlear– VI Abducens

Eyeball

External Walls“tunics”

Outer Sclera• White CT • “White” of the eye

Outer Sclera• Central anterior is clear and

forms cornea

Outer Sclera•Cornea can be transplanted

– no blood vessels

Vascular Tunic• Blood-rich for nutrition•Lens attaches to anterior end

“ciliary body”

Sensory Tunic• Called - Retina• Contains rods and cones • Sensory photoreceptors

Sensory Tunic• Impulses leave by optic nerve• No photoreceptors where

optic nerve leaves - “blind spot”

Rods• Gray tones• Fx: Dim light & Peripheral

vision• Loss: Night blindness• Usually vitamin A deficiency

Cones• Color details• Heaviest in center of retina –

fovea centralis– sharpest vision spot

Cones & Colors

• Blue, Red, & Green• More than one type firing –

intermediate colors–Red & Blue = Purple

Cones & Colors

• If all 3 firing = white• If none firing = black• Color interpretation in Brain

NOT retina

Colorblindness

• If lack all 3 cones – colorblind– See shades of gray

•If lack one cone – partial colorblindness

Colorblindness

• Most common is lack of red or green

• Color vision genes – X chromosome– Sex-linked– Almost always males

Lens

•Focuses light on retina• Turns opaque as we age• Can lead to cataracts

Cataracts

Chambers of Eye

•Liquid (humor) hold shape of eyeball

• Lens divides into 2 chambers• Anterior – aqueous humor•Posterior – vitreous humor

Chambers of Eye• Anterior –

aqueous humor– like plasma– nutrients for

lens and cornea– Constantly

formed and drained

Chambers of Eye

•If drain blocked, increases pressure

• Glaucoma

Chambers of Eye

•Posterior – vitreous humor– Gel-like protein

– Not replaceable

Focusing the Eye•Lens changes shape to focus

image on retina = accommodation

Focusing the Eye

•Myopia– Short vision– Focuses in front of retina

– Distant objects appear blurry

Focusing the Eye

•Hyperopia– Far vision– Focuses beyond retina

– Close objects appear blurry

Focusing the Eye

•Presbyopia– “Old eye” (40’s)– Lens hardening– Cannot accommodate “near vision”

– Hold it out further

Focusing the Eye

•Astigmatism– Unequal curvature of cornea or lens

– Focus point different for each eye

Visual Nerve Path

•Retina → Axons →

Form bundles of axons →

Form Optic Nerve

Visual Nerve Path

•At Optic chiasma– Lateral fibers stay on same side of brain

– Medial fibers cross over to other side of brain

Visual Nerve Path

Visual Nerve Path

•Lateral and medial fibers form optic tract (left & right)

Visual Nerve Path

•Optic tract synapses with thalamus

•Form optic radiation on occipital lobe– Visual interpretation

Documents