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Cranial Nerves Exam 1 Cheat Sheet (DRAFT) by

Optic Nerve

This is a draft cheat sheet. It is a work in progress and is not finished yet.

Oculomotor Nerve

Ocular­motor Nucleus
Nucleus is located in the mesenc­ephalon at the level of the superior colliculi, in front of the periaq­ued­uctal gray matter.
Innerv­ation
Medial, Superior, Inferior rectus muscle. Inferior Oblique. Levator palpevrae superioris
Edinge­r-W­estphal Nucleus
Parasy­mpa­thetic fibers -->­cillary gangli­on-­->s­phi­ncter of the pupil & cillary muscle
Perlia Nucleus
Located between the EW nucleus -->­Con­ver­gence of the eyes
Inters­itital nucleus of Cajal
Interg­rates vertical gaze

Oculomotor Nerve Lesions

Symptoms
Dialation of Pupil, No direct or indirect pupilary light reflex, no accomi­dation refex, ptosis
Nuclear Lesion
Midbrain lesions
Nerve Lesion
Suprat­ent­orial space occupying lesion causes transt­ent­orial herniation of the medial temporal lobe (uncus) and Compresses the ocular­motor nerve
Argyll­-Ro­bertson Pupils
Bilateral loss of pupliary light reflex, but no loss of accomi­dation --> Tertiary Syphilis, MS, Diabetes, Syring­obu­lbia, Pineal Tumor
Adie Syndrome
Very slow constr­iction and accomo­dation --> widespread autonomic distur­bance or neuropathy (effects young women)

Visual Acuity Exam

Visual acuity is tested with Snellen charts -
6 lines at 6 meters away.
If the patient normally wears glasse­s/l­enses, then this test should be assessed both with and without their vision aids.
If there is marked loss of acuity, examiner should determine distance at which patient is able to count fingers.

Visual Field Exam

The field of vision is the space in which an object can be seen while the eye remains fixed at one point.
Lateral: 90-100 Medial: 60 Upward: 50-60 Downward: 60-75
Confro­ntation Method
Cover one of the patients eyes, ask patient to fix sight on your nose, bring your finger into the field of vision from all four direct­ions, asking them to respond when they see it. --> Detects Hemian­opias
, Two Eye Confro­ntation Method
Using both eyes, ask patient to fix sight on your nose, out strech your arms and ask pacient to grab your finger when hands come into visual field. --> Temporal field defect if doesnt grab finger until crosses midline --> can also detect visual neglect

Visual Field Defects

Concentric Contra­ction
Narrowing of the range of vision on all sides -->­Optic Atrophy
Homonymous Hemianopia
Loss of vision on temporal half of one eye (ipsil­ateral to lesion) and nasal half of the other eye --> Lesion posterior to optic chiasm
Wernicke's Hemianopia Phenomenon
Also loss of pupilary light reflex in the effected side of the retina because lesion is after ocular motor nucleus
Hetero­nymous Hemianopia
Loss of vision in either both nasal, or both temporal fields --> Damage to the optic chiasm (Superior visual field effected first)
Bitemporal Hemianopia
Caused by pituitary adenomas, or any other parase­lla­r/s­upr­asellar tumors- mening­iomas, cranio­pha­ryn­giomas. Also aneurysms, trama, and hydroc­eph­alus.
Binasal Hemianopia
Rare, caused by athero­scl­erosis, or bilateral aneurysms of the internal carotid, and in demyel­inating disorders.
Horizontal Hemian­opias
Very rare, Unilateral loss of the lower half of the visual field -->­Anerior lesion of the optic nerve in ischemia of the optic nerve head.
Quadra­nta­nopia
Loss of one quadrant in the field of vision. Lower quadra­nt-­->D­amage to fibers radiating through parietal lobe and terminate on upper lip of the calcarine fissure. Upper quadrant -->­Damage to fibers radiating through temporal lobe (Meyers loop) and terminate on lower lip of calcarine fissure.
Cortical blindness
Bilateral lesions of the primary visual cortices
Scotomas
Blind spots in the field of vision. (+) are seen as dark spots by patients. (-) are not noticed by the pacient. --> Disease of retina or optic nerve

Examin­ation of Ocular Movements

Position of eyes when looking straight ahead
Note any deviation
Verbal Commands
Ask patient to look L R U D
Pursuit Movements
Fix patients head and ask them to follow your finger as it moves the 9 cardinal positions of gaze.
 
Is the gaze conjugate, are there restricted movements, nystagmus, or diplopia?
Vergence Movements
Have the patient focus on your finger 60cm away, then as its gradually brought closer.
Vestib­ulo­-Ocular Reflex
Have patient fix eyes on a target while you passively move their head side to side and up and down. The gaze should remain stable. Can also preform the calori­sation test.
Caloric Reflex Test
Introduce warm water (44°C or above) into the external auditory canal. It will cause the endolymph in the ipsila­teral horizontal canal rises, causing an increased rate of firing in the vestibular afferent nerve. This situation mimics a head turn to the ipsila­teral side. Both eyes will turn toward the contra­lateral ear, with horizontal nystagmus (quick horizontal eye movements) to the ipsila­teral ear if brainstem intact.
Saccasdes
Ask the patient to fix their gaze, then alternate it between objects. What is the accuracy and velocity? Are there corrective saccades?
 

Trochlear Nerve

Trochlear Nucleus
Located in the midbrain at the level of the inferior colliculli in the periaq­ued­uctal grey matter directly below the ocular­motor nerve. Its fibers cross and leave the midbrain dorsally. (only one)
Innervates
Superior Oblique (contr­ala­teral due to crossing)
Nuclea­r/Nerve Lesion
Most common­--> direct facial trama. Also brainstem contusion, MS, rupture of posterior cerebral aneurysms or superior cerebellar artery, cavernous sinus disorders.
Bielsc­howsky sign
Symotoms - Head tilted to normal side, upon tilting the head to the abnormal side, diplopia becomes prononced

Abducens Nerve

Abducens Nucleus
Is located in the midline of the tegmentum of the lower pons beneath the floor of the IV ventricle. The internal knee of th facial nerve wraps around it. The nerve leaves the pns and runs up the clivus and joins the III and IV nerve in the cavernous sinus.
Innerv­ation
Lateral Rectus Muscle
Nuclear Lesion
Bilateral paralysis due to paramedial pontine infraction due to basilar artery stenosis with ipsila­teral paralysis of conjugate gaze because the abducens nucleus also innervates via the medial longit­udinal fasciculus the contra­lateral medial rectus muscle.
Nerve Lesion
Bilateral paralysis due to increased ICP. Ipsila­teral paralysis due to Wernic­ke-­Kor­sakow syndrome, Miller Fisher syndrome, neurob­orr­eliosis (lymes disease) and botulism toxicity.
 

Voluntary Vertical Eye Movements

Cortical Center
Dorsol­ateral Prefrontal Cortex­->a­nterior limb of the internal capsul­e->­rostral inters­titial nucleus of MLF
Parinaud Syndrome
Unable to look upward -->­Pineal Tumor compre­ssing the posterior commisure

Voluntary Horizontal Eye Movements (Sarcc­ades)

Cortical Center
Fibers leaving the Frontal Eye Field (Broadman 8) cross at the midbra­in/pons border and terminate in the Pontine Reticular Formation -> Abducens Nucleus -> Medial Longit­udinal Fascicle to the contra­lateral Oculomotor Nucleus.
Intern­uclear Opthal­mop­legia