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

Nuc

lei I

mpo

rtan

t to

Ocu

lom

otor

Fun

ctio

n

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)

Basic Eye Exam

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