Senses Vision

V 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”

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

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