Cranial nerve I and IIDr Parag Moon

Senior Resident,Dept. Of Neurology,

GMC Kota.

Anatomy First order neurons-bipolar sensory cells in

olfactory epithelium (superior nasal concha, upper nasal septum, roof of the nose)

Tiny knobs on cilia-sites of chemosensory signal transduction.

Specific odorants stimulate specific receptor cells.

Central processes of olfactory neurons-unmyelinated axons

Olfactory nerve

Form approximately 20 branches on each side-olfactory nerves.

Penetrate cribriform plate of ethmoid bone, acquire a sheath of meninges, synapse in olfactory bulbs.

Basal cells in olfactory epithelium can regenerate.

Within olfactory bulbs, synapse on dendrites of mitral and tufted cells in olfactory glomeruli.

Second order neurons-axons of mitral cells Course posteriorly through olfactory tracts

in olfactory grooves beneath frontal lobes Divide into medial and lateral olfactory striae. Medial olfactory stria terminate on medial

surface of cerebral hemisphere in paraolfactory area, subcallosal gyrus and inferior part of cingulate gyrus.

Lateral olfactory stria terminate in uncus, anterior hippocampal gyrus, piriform cortex, entorhinal cortex, and amygdaloid nucleus

History◦ Unilateral or bilateral◦ Altered taste◦ Past head injury;◦ Smoking◦ Recent upper-respiratory infection◦ Systemic illness◦ Nutrition◦ Exposure to toxins, medications or illicit drugs.

CLINICAL EXAMINATION

Before evaluating smell- nasal passages are open.

Smell is tested using nonirritating stimuli. Avoid irritating substances-stimulate trigeminal

nerve Examine each nostril separately while occluding

other with eyes closed Perception more important than accurate

identification University of Pennsylvania smell identification

test (UPSIT) and Connecticut chemosensory test..

Term Definition

Anosmia No sense of smellHyposmia decrease in the sense of smellHyperosmia overly acute sense of smellDysosmia Impairment or defect in the sense of smell

Parosmia Perversion or distortion of smellPhantosmia Perception of an odor that is not realPresbyosmia Decrease in the sense of smell due to agingCacosmia Inappropriately disagreeable odorsCoprosmia fecal scentOlfactory agnosia

Inability to identify or interpret detected odors

Causes of anosmia/ hyposmia

Smoking Pregnancy Chronic rhinitis Dental trauma Deviated nasal septum Intranasal tumors (e.g., epidermoid

carcinoma) Neuro-olfactory tumor

(esthesioneuroblastoma) Nasal polyps Antihistamines Propylthiouracil Olfactory dysgenesis Cadmium toxicity Chemical burns of the olfactory

epithelium Vitamin deficiency (B6, B12, A) Postviral Zinc or copper deficiency General anesthesia Kallmann's syndrome

Olfactory groove meningioma Craniocerebral trauma,

including surgery Frontal lobe tumor, especially

glioma Alzheimer's disease Parkinson's disease Normal aging Multiple sclerosis Sellar/parasellar tumor Congenital anosmia Meningitis Korsakoff's syndrome Familial dysautonornia Temporal lobectomies Refsums disease

5 cm in length Extends from ganglion cell layer of retina to

optic chiasm. Divided into

◦ Intraocular:1mm◦ Intraorbital:25mm◦ Intracanalicular:9mm◦ Intracranial:12-16mm

Organized into 400 to 600 fascicles separated by connective tissue septae.

Intraorbital portion-surrounded by fat

Optic nerve

Macula-point of central fixation and greatest visual acuity and color perception.

Small shallow depression temporal to disc Fovea (L. “pit”) centralis-depression that

lies in center of macula. Foveola-tinier depression in center of fovea. Point of most acute vision as overlying

retinal layers are pushed aside Optical center of eye Macula-central 15° of vision

Optic nerve

Optic disc, or papilla-ophthalmoscopically visible tip of intraocular portion of optic nerve.

1.5 mm by 1.8 mm vertical ellipse Pink to yellowish-white disc. No receptor cells Does not respond to visual stimuli-

physiologic blind spot Macula-forms center of retina Macular fixation point-center of clinical

visual field (VF).

Blood supply to optic nerve head-circle of Zinn-Haller,

Composed of 2 often not connected semicircles of short posterior ciliary arteries.

NAION- drop in perfusion pressure in short posterior ciliary arteries is culprit.

Segmental disc edema corresponding to the semicircle compromised

Retinal ganglion cell axons form retinal nerve fiber layer (NFL)

Exit through lamina cribrosa (L. “sieve”) Myelinated at posterior end of optic nerve

head Myelin-CNS myelin 1.2 million fibers in each optic nerve;

Intracranial dura at posterior globe fuses with Tenon's capsule

Adherent in optic foramen to periosteum. Pia and arachnoid fuses with sclera where nerve

terminates Intracranial meninges extend forward along

optic nerves for a variable distance, forming vaginal sheaths.

Variations in vaginal sheath anatomy Intervaginal space-small subdural and a

larger sub-arachnoid space

Intraorbital portion-lies within muscle cone. Before entering optic canal, surrounded by

annulus of Zinn formed by origins of rectus muscles.

Superior and medial recti partially originate from sheath of optic nerve.

Length of intraorbital portion greater than length of orbit

Blood supply-pial vascular plexus and branches of ophthalmic artery; distally central retinal artery also contributes intraneural branches.

Intracanalicular portion-into cranium through optic canal

Orbital opening of canal-vertical ellipse; intracranial end-horizontal ellipse

1.2 cm in length, and located in lesser wing of sphenoid bone.

Dural sheath fused to periosteum-immobilizing nerve.

Medial wall of canal-thinnest part Blood supply-ophthalmic artery.

Intracranial portion-travel 12-16 mm to optic chiasm.

Ophthalmic arteries above, internal carotid arteries superiorly and medially, and anterior cerebral arteries that cross over optic nerves and are connected by anterior communicating artery.

Posterior to cavernous sinus-join together to form optic chiasm;

Blood supply-branches of internal carotid and ophthalmic arteries.

Optic chiasm-lies about 10 mm above pituitary gland, separated by suprasellar cistern.

Fibers from temporal retina continue directly back: nasal retina decussate to enter opposite optic tract.

Fibers from inferior nasal quadrant loop forward into opposite optic nerve for a short distance before turning back again, forming Wilbrand's knee.

Some of upper nasal fibers loop back briefly into ipsilateral optic tract before decussation.

In chiasm, fibers from upper retinal quadrants lie superior: lower quadrants inferior

Inferior nasal fibers decussate anteriorly and inferiorly: superior nasal fibers cross posteriorly and superiorly

Macular fibers-decussate as a group, forming a miniature chiasm within chiasm,

primarily posterior superior portion.

Cavernous sinuses and carotid siphons lie just lateral to chiasm

Anterior cerebral and anterior communicating arteries front and above

Third ventricle and hypothalamus behind and above. Sella tursica and sphenoid sinus lie below. Ophthalmic artery-same dural sheath through

canal and orbit. 8 mm to 12 mm posterior to globe, artery enters

nerve and runs along its center to optic disc-central retinal artery

Divides at disc head into superior and inferior branches.

55% of axons of optic tract- contralateral nasal retina; 45% ipsilateral temporal retina

80% visual afferents and 20% pupillary afferents.

Fibers from upper retina-medial position, inferior retina lateral.

PMB-dorsal and lateral position, Majority of fibers terminate at LGB. Six neuronal layers in the LGB Ipsilateral temporal hemiretina synapse in

layers 2, 3, and 5;contralateral nasal hemiretina synapse in layers 1, 4, and 6.

Geniculocalcarine tract, or optic radiations

Terminate in calcarine cortex of occipital lobe

Pass through retrolenticular portion of internal capsule and then fan out.

Upper retinal fibers upper, and lower retinal fibers lower in optic radiation

Inferior retinal fibers arch anteriorly into temporal lobe, sweeping forward and laterally above inferior horn of ventricle then laterally, down, backward.

Meyer's loop (loop of Meyer and Archambault).

Fibers from superior retina run directly back in deep parietal lobe in external sagittal stratum, lateral to posterior horn of lateral ventricle

Primary visual cortex (calcarine area or striate cortex)-Brodmann's area 17 on medial surface of occipital lobe.

Lower retinal fibers- lower lip of calcarine fissure (lingual gyrus)

Upper retinal fibers-upper lip of the calcarine fissure (cuneus).

Most peripheral parts of retina-most anteriorly in calcarine cortex

Macular -More posterior its calcarine representation.

Visual acuity◦ Minimum visibility-smallest area that can be

perceived◦ Minimum separability-ability to recognize the

separateness of two close points or lines◦ Snellen chart for distance and near card for near◦ In infants and children- blink to threat or bright

light, following movements, pupillary reactions◦ Acuity- line where more than half of characters

are accurately read

Clinical examination

Distance from test chart, 20 or 6-numerator, and distance at which smallest type read by patient should be seen by a person with normal acuity-denominator.

RAPD or Marcus gunn pupil◦ Swinging light test◦ Light shone into a pupil and then quickly switched

to other one.◦ If one pupil dilates, even slightly, when light is

switched-RAPD present in that eye.

Near vision Jaeger chart Newspaper want-ad text is approximately J-

0, regular newsprint J-6, and newspaper headlines J-17.

Counts fingers (CF), hand motion (HM), light perception (LP), or no light perception (NLP).

Count fingers at 5 ft-20/800.

Non organic visual loss1. Ask to sign2. Schmidt-Rimpler test- look toward his

hand3. Join the forefingers4. Menace test5. Ask patient look into a large mirror that

can be held and moved. Tilting and moving the mirror will elicit OKN responses

Color Vision; Day and Night Vision Color plates or pseudoisochromatic plates

(Ishihara, Hardy-Ritter-Rand ) In neurologic disease, red perception

usually lost first Compare brightness or intensity of

examining light in one eye versus other

Visual field Normal VF- 90 degrees to 100 degrees

temporally, about 60 degrees nasally, 50 degrees to 60 degrees superiorly, and 60 degrees to 75 degrees inferiorly

Examination most accurate in an individual who is alert and cooperative and maintain fixation.

Confrontation test Moving pen light Menace reflex

Formal visual field testing Central fields-tangent screen Peripheral fields-perimetry Notation numerator-test object size and

denominator-distance from screen

Kinetic perimetry entails moving a test object along various meridians and noting when it is detected.

E.g., Goldmann White and colored test objects varying in size

from 1 mm to 5 mm Smaller test object, smaller VF. If size of a VF defect is same with all test

objects-steep, or abrupt, margins. If larger with smaller test objects-gradual, or

sloping margins

Automated static perimetry Humphrey Visual Field Analyzer Normal patients may appear to have

abnormal VF due to large number of erroneous responses that can occur during automated testing

Direct opthalmoscopy Small aperture-examining an undilated

pupil, large aperture-dilated pupil Red-free filter-examining blood vessels,

looking for hemorrhages, and nerve fiber layer

Red reflex-assessed from distance of 12 in to 15 in.

Areas of primary concern- disc, macula, and arteries

Disc normally round or vertically oriented slight oval.

Nasal margin slightly blurred Peripheral neuroretinal rim and central cup. Physiologic cup-slight depression in center

of disc that is less pinkish than rim and shows a faint latticework due to underlying lamina cribrosa.

Rim is elevated slightly above cup.

Myelinated axons-normal optic disc yellowish white.

Paler temporally where papillomacular bundle (PMB) enters.

When scleral opening small, disc consists entirely of neuroretinal tissue, and inconspicuous or nonexistent cup.

More vulnerable to anterior ischemic optic neuropathy-disc at risk.

Normal cup-to-disc ratio-0.1 to 0.5.

Macula-dark area that lies about 2 disc diameters temporal to and slightly below disc.

Appears darker than surrounding retina because of thinner retina

Area of macula devoid of large blood vessels. Fovea centralis appears pinpoint of light

reflected from center of macula. Macula may be seen more easily with a red-

free filter, if patient looks directly into light

Photostress Test In macular disease, photoreceptors require

longer to recover from bleaching of retinal pigments after exposure to a bright light.

Baseline visual acuity Then shining a bright light (e.g., a fresh

penlight) into eye for 10 seconds Determine time required for visual acuity to

return to baseline. Mainly useful with unilateral disease Optic nerve disease-normal photostress test.

Papilledema Four stages of -early, fully developed, chronic, and atrophic.

Fully developed-elevation of disc surface, humping of vessels crossing disc margin, obliteration of disc margins, peripapillary hemorrhages, cotton wool exudates, engorged and tortuous retinal veins, and marked disc hyperemia

Early papilledema-loss of previously observed spontaneous venous pulsations (SVPs).

SVPs=200 mm H2O ICT

Pseudopapillodema Common causes-optic nerve drusen,

myelinated nerve fibers, remnants of primitive hyaloid artery (Bergmeister's papilla), tilted discs, extreme hyperopia.

Optic nerve drusen, or hyaloid bodies◦ Acellular, calcified hyaline deposits within optic

nerve that may elevate and distort disc. ◦ Present 2%, bilateral in 70%◦ Highly refractile, rock-candy appearance.

In papilledema-1. disc is usually hyperemic;2. margin blurriness at superior and inferior poles early

in process; 3. blood vessels look normal except for fullness of veins; 4. NFL is dull with retinal blood vessels obscured

because of retinal edema. In pseudopapilledema

1. disc color remains normal; 2. blurriness of disc margin may be irregular,disc may

have a lumpy appearance;3. blood vessels on the disc frequently look anomalous; 4. NFL is clear.

If in doubt, consult an ophthalmologist.

Optic neuritis Ischemic optic neuropathy Optic nerve compression Papillophlebitis Optic nerve infiltration (carcinomatous, lymphomatous) Sarcoidosis Diabetic papillopathy Tobacco-alcohol amblyopia Nutritional deficiency, especially vitamin B12 Drugs Toxins Hereditary optic neuropathy (Leber, Kjer) Glaucoma

Causes of optic atrophy

Chiasmal Lesions◦ Pituitary tumors◦ Craniopharyngiomas◦ Meningiomas◦ Gliomas◦ Carotid aneurysms ◦ Demyelination◦ Ischemia◦ Radionecrosis

Thanks

Inderbir Singh's Textbook of Human Neuroanatomy (Fundamental and Clinical)

DeJong’s The Neurological Examination, Sixth Edition

Optic Nerve: Anatomy, Function, And Common Disorders;edward A. Margolin, Rajeshvar K . Sharda;Ophthlmology Rounds; May/June 2014 Volume 6, Issue 3

The optic nerve: a clinical perspective;Pasquale Montaleone;UWOMJ | 79:2 | Fall 2012

References