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Gross Anatomy of the Eye • Cornea at anterior – Light passes to lens • Retina at posterior – sensory tissue – sensory cells: rods and cones 1. Cornea 2. Lens 3. Iris 4. Sclera 5. Macula 6. Optic Nerve Head 7. Retinal vessels Sup. 8. Vortex Veins Lat. Med. 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 Anatomy 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 YAW Eye Movements Yaw: gaze shifts L/R Pitch: gaze shifts up/down Roll: eye rotates around line of gaze (torsion) PITCH ROLL • Adduction: shifting gaze toward midline • Abduction: shifting gaze laterally Extraocular Muscles Anterior View of Left Orbit Oculomotor Muscle Actions Muscle Action Nerve Supply Sup. rectus elevates & abducts eyeball upper division of oculomotor n. (III) Sup. oblique depresses & abducts eyeball trochlear n. (IV) Med. rectus adducts the eyeball lower division of oculomotor n. (III) Lat. rectus abducts the eyeball abducens n. (VI) depresses & abducts eyeball lower division of oculomotor n. (III) elevates & abducts eyeball lower division of oculomotor n. III) raises the eyelid upper division of oculomotor n. (III) Inf. rectus Inf. oblique levator palpebrae superioris Sup. Post. Ant. Inf. 3 branch of CN III to Inf Obl. 5 Sup. Rectus 7 Inf Rectus 8 Optic Nerve 10 Abducens Nerve 11 Oculomotor Nerve (CN III) Ocular Musculature Superior Rectus (SR) Inferior Rectus (IR) Lateral Rectus (LR) Medial Rectus (MR) Superior Oblique (SO) Inferior Oblique (IO) CN Nuclei Important to Oculomotor Function 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 & Physiology of a Horizontal Saccade Saccades Pause cells inhibit Burst Neurons which stimulate: III & VI (horizontal) or III & IV (vertical)