Gross Anatomy of the Eye
• Cornea at anterior– Light passes to lens
• Retina at posterior– sensory tissue– sensory cells: rods
and cones
1. Cornea1. Cornea
2. Lens2. Lens
3. Iris3. Iris
4. Sclera 4. Sclera
5. Macula 5. Macula
6. Optic Nerve Head 6. Optic Nerve Head
7. Retinal vessels 7. Retinal vessels
8. Vortex Veins8. Vortex VeinsMed.Lat.
Sup.
Inf.
Looking at the Retina
Macula- 3 by 5 mm area at the posterior pole of the eye
Fovea- in center of macula,
free of blood vessels
contains only cone cells
Retinal Retinal AnatomyAnatomy
Back of the Eye
Front of the Eye
Extrinsic Eye Musculature
For moving eye within its socket.
6 muscles per eyeball
Innervated by 3 Cranial nerves
Eye Movements
Yaw: gaze shifts L/R
Pitch: gaze shifts up/down
Roll: eye rotates around
line of gaze (torsion)
• Adduction: shifting gaze toward midline
• Abduction: shifting gaze laterally
PITCH
YAW
ROLL
Extraocular Extraocular MusclesMuscles
Anterior View of Left OrbitAnterior View of Left Orbit
Oculomotor Muscle Actions
Muscle Action Nerve Supply
Sup. rectus elevates & abducts eyeballupper division of
oculomotor n. (III)
Sup. oblique depresses & abducts eyeball trochlear n. (IV)
Med. rectus adducts the eyeballlower division of
oculomotor n. (III)
Lat. rectus abducts the eyeball abducens n. (VI)
Inf. rectus depresses & abducts eyeballlower division of
oculomotor n. (III)
Inf. oblique elevates & abducts eyeballlower division of
oculomotor n. III)
levator palpebrae superioris raises the eyelid
upper division of oculomotor n. (III)
3 branch of CN III to Inf Obl.5 Sup. Rectus7 Inf Rectus8 Optic Nerve10 Abducens Nerve11 Oculomotor Nerve (CN III)
Ant.Post.
Sup.
Inf.
Ocular Musculature
Superior Rectus (SR)
Inferior Rectus (IR)
Lateral Rectus (LR)
Medial Rectus (MR)
Superior Oblique (SO)
Inferior Oblique (IO)
CN
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Ocu
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Fun
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Cranial Nerves III, IV, and VI
• III - Oculomotor
• IV - Trochlear
• VI - Abducens
III (Oculomotor) innervates:
1) Medial rectus
2) Superior rectus
3) Inferior rectus
4) Inferior oblique
Levator palpebrae sup
Pupillary sphincter
Ciliary muscle
IV (Trochlear) innervates:
• Superior oblique
VI (Abducens) innervates
• Lateral rectus.
Proprioceptive info from eye muscles
• comes through Trigeminal nerve.
Eye Movements
• Saccades—rapid shift in gaze• Pursuit—stabilize image of moving object• Fixation—stabilize image of still object• VOR—stabilize image during head motion• OKN—backup for when VOR decays to cont’d
head rotation• Vergent movements—change depth of focus
– Accommodation-- automatic changes to see at different distances which is chiefly brought about by changes in the convexity of the lens. Horizontal vergence and accommodation normally occur together. The two responses are accompanied by an appropriate change in pupil diameter. The three concomitant changes are known as the near-triad response.
Cortical Areas:
Oculomotor Control
• Occipital Eye Fields (areas 18 and 19) • Frontal Eye Fields (area 8) • Temporal Eye Fields (area 22)
Vestibulo-Ocular Reflex
VOR Pathways
• Vestibular nuclei
• Abducens N.
• Median Longitudinal Fasciculus
• Trochlear N.
• Oculomotor N.
Horizontal/Lateral Canal VOR
Anterior/Superior Canal VOR
Posterior Canal VOR
Anatomy & Anatomy & Physiology of Physiology of a Horizontal a Horizontal SaccadeSaccade
Pause cells inhibit
Burst Neurons
which stimulate:III & VI (horizontal)
or
III & IV (vertical)
Saccades
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