Optic Nerve/Neuro-ophthalmic Pathways Flashcards

Question

Which of the following cranial nerves is affected in a patient diagnosed with Bell's palsy? ``` Eighth cranial nerve Fifth cranial nerve Third cranial nerve Eleventh cranial nerve Seventh cranial nerve Ninth cranial nerve ```

Answer 1

Seventh cranial nerve Explanation Bell's palsy is an idiopathic isolated peripheral palsy of the ipsilateral seventh cranial nerve (facial nerve). It is thought that inflammation of the nerve results in compression of the fibers where it exits the skull within its bony canal, thereby blocking the transmission of neural signals.

Answer 2

Optic nerve hypoplasia Explanation Patients with optic nerve hypoplasia present with several characteristic funduscopic features that comprise its diagnosis. Classically, the optic disc is small, has a greyish appearance, and is surrounded by a mottled, yellow, hypo-pigmented peripapillary border that encircles the disc, forming a halo. This halo is also bordered by a darker pigmented ring, which leads to the name "double ring sign." The outer ring represents what would have been the margin of the disc had it been of normal size.

Answer 3

Ophthalmic division Explanation The most frequently affected branch of the trigeminal nerve in herpes zoster infections is the ophthalmic division (V1) with its supraorbital, lacrimal and nasociliary distributions. The ophthalmic nerve carries sensory information from the scalp and forehead, the upper eyelid, the conjunctiva and cornea, the nose (including the tip of the nose), the nasal mucosa, the frontal sinuses, and part of the meninges.

Answer 4

Cranial nerve III Cranial nerve IV Cranial nerve XI Cranial nerve VI Explanation Cranial nerves I (olfactory), II (optic), and VIII (vestibulocochlear) are sensory in function. Cranial nerves III (oculomotor), IV (trochlear), VI (abducens), XI (spinal-accessory) and XII (hypoglossal) have exclusively motor functions. Cranial nerves V (trigeminal), VII (facial), IX (glossopharyngeal) and X (vagus) possess both motor and sensory functions. A good mnemonic is: Some Say Marry Money But My Brother Says Big Brains Matter More (The words correspond to the cranial nerves in proper numerical order, with all 'S' words representing sensory function: 'M' words depict exclusive motor function, and 'B' words signify nerves with both motor and sensory function).

Answer 5

Papilledema Explanation Papilledema is defined as passive swelling of the optic disc caused by increased intracranial pressure, usually as a result of intracranial tumors or malignant hypertension. The condition is almost always bilateral, and vision is usually normal unless there is associated edema or exudates in the macular area. Optic neuritis is inflammation of the optic nerve that can occur at any location as it courses from the eye. It is typically caused by swelling and destruction of the myelin sheath that surrounds the nerve. Papillitis is a specific type of optic neuritis in which there is an inflammation of the optic nerve head. This condition is almost always unilateral, and because the optic nerve is inflamed, it is commonly associated with vision loss. Ischemic optic neuropathy is caused by obstruction of blood flow to the optic nerve, resulting in the loss of structure or function of a portion of the nerve. It is classified as either arteritic or non-arteritic, according to the location of the nerve that is affected. Patients with this condition will often present with acute loss of visual acuity and an altitudinal visual field defect.

Answer 6

Short posterior ciliary arteries Explanation The ophthalmic artery provides the majority of the supply of blood to both the inner retina and the optic nerve. - The central retinal artery (CRA) branch of the ophthalmic artery enters the optic nerve approximately 12mm behind the globe - In the retina, the retinal ganglion cell bodies and the nerve fiber layer are primarily supplied by capillary branches of the central retinal artery that emerge from the optic nerve head - As the CRA courses over the optic disc, it provides partial perfusion to some of the superficial optic disc; however, it provides minimal perfusion to the optic nerve itself, through which it courses - Branches of the medial and lateral short posterior ciliary arteries (SPCAs) also originate from the ophthalmic artery - These provide the majority of the blood supply to the optic nerve head as well as the choroid - Most notably, anastomoses of the SPCAs create the Circle of Zinn-Haller, which provides significant perfusion to the optic nerve head

Answer 7

Optic nerve -> optic chiasm -> brachium of the superior colliculus -> pretectal region of the midbrain -> Edinger-Westphal nucleus Explanation The pupillary fibers exit the eye through the optic nerve and pass through the optic chiasm, where they then exit the optic tract and enter into the brachium of the superior colliculus and synapse onto cells in the pretectal area of the midbrain. The pathway then continues and stimulates intercalated neurons, which in turn stimulate cells in the Edinger-Westphal nucleus. The axons of the pupillary pathway never enter the lateral geniculate nucleus.

Answer 8

Microvascular third nerve palsies do not typically involve the pupil Third nerve palsies associated with microvascular disease commonly spontaneously resolve within 3 months Explanation There are several signs and symptoms that clinicians utilize in order to aid in differentiating between microvascular and compressive third nerve palsies. Some of these are summarized below: - Third nerve palsies associated with microvascular disease commonly spare the pupil due to the superficial location of pupillary fibers as they travel in the nerve - Third nerve palsies associated with compressive lesions commonly involve the pupil due to compression of the superficial pupil fibers - It is important to note that this is only a general principle; there are several cases in which compressive lesions do not affect the pupil initially but may eventually if the lesion continues to grow (also, some diabetic palsies have been shown to cause pupil dilation) - Third nerve palsies due to microvascular lesions will typically resolve within a period of three months (if a suspected microvascular lesion does not resolve within this time, imaging must be completed) - Aberrant regeneration will only occur following acute traumatic or compressive third nerve palsies (but never after a microvascular palsy) due to the fact that the endoneural nerve sheaths remain intact in vascular pathology - The presence of pain is common in both diabetic and aneurysmal third nerve palsies; therefore, it cannot be used to differentiate the two

Answer 9

There is no clinical condition in which this exists Explanation The near reflex is activated when a person changes gaze from a distant to a near object. It is comprised of a triad of accommodation, convergence, and pupil miosis. Vision is not required for this response, and there is no clinical condition in which the pupillary light reflex is intact and the near response is absent. However, there are several conditions that are associated with dissociation of light and near responses in which the light reflex is either absent or sluggish and the near response is normal. Although the final pathways for both responses are identical, the center for the near reflex is controlled by a supranuclear influence.

Answer 10

Hypothalamus--> ciliospinal center of Budge--> superior cervical ganglion--> ophthalmic division of trigeminal nerve Explanation The oculosympathetic pathway contains three neurons as it courses from the brain to structures of the eye. The first neuron (central neuron) in this pathway begins at the posterior region of the hypothalamus. It descends down the brainstem to synapse at the ipsilateral ciliospinal center of Budge, which lies between C8 and T2 of the spinal cord. The second neuron (pre-ganglionic neuron) traverses a long course from the ciliospinal center to the superior cervical ganglion in the neck region. During its path, it is closely related to the apical area of the lung where it can be damaged by a Pancoast tumor, or in some cases, during surgery on the neck. The final neuron in the oculosympathetic pathway (post-ganglionic neuron) ascends with the internal carotid artery where it eventually enters the cavernous sinus and joins with the ophthalmic division of the trigeminal nerve. From here, the sympathetic fibers reach the pupil dilator and ciliary body by means of the long ciliary nerves and nasociliary nerves.

Answer 11

Inferiorly Explanation The nerve fiber layer is thickest at the inferior and superior regions of the nerve, respectively. The inferior and superior arcades are composed of large diameter axons with little overlap of the receptive fields, thus explaining why a field defect occurs in these regions first for early cases of glaucoma. Inferior or superior notching of the nerve is highly suspect for glaucomatous damage, and must undergo further testing in order to rule out glaucoma. The next thickest area of nerve fiber layer tissue is nasally, which is comprised of the nasal radial fibers. These axons are affected in the later stages of glaucoma, thus explaining why a temporal island of the visual field is often left remaining in advanced cases of glaucoma. Lastly, the temporal rim area is the thinnest. Temporal rim tissue is comprised of the papillomacular bundle. The fibers in this area are very small and compact, with a high degree of receptive field overlap, therefore because of the receptive field redundancy, a visual field defect correlating to this region will occur only after significant fiber loss has occurred. Due to the fact that these fibers are so small in diameter, even though they are numerous, the fibers do not occupy a lot of space in the optic nerve. The thickness of the nerve fiber layer rim tissue is best remembered as ISNT, with inferior being the thickest and temporal rim tissue being the thinnest.

Answer 12

The nerve fiber layer Explanation The nerve fiber layer is the only layer of the retina that is present at the optic disc. The disc serves as the convergent point for axons of the nerve fiber layer which then form the optic nerve to convey visual information to the brain for further processing. The actual optic disc does not contain photoreceptors and thus will not generate nervous signals. This explains why this area is also known as the 'blind spot'.

Answer 13

Cranial nerve V Cranial nerve III Explanation Marcus-Gunn jaw winking is a phenomenon that is thought to occur as a result of an abnormal connection between cranial nerve V and cranial nerve III. Branches from the motor root of the trigeminal nerve that are meant for the ipsilateral pterygoid muscle aberrantly connect with the ipsilateral levator muscle instead. This allows for an elevation effect of the upper eyelid when jaw movements are initiated. This type of aberrant innervation may occur in up to 5% of patients presenting with a congenital ptosis; it tends to lessen in severity with age. This condition should not be confused with aberrant regeneration of cranial nerve VII; it is an isolated neurologic finding and does not require further work-up. Furthermore, Marcus-Gunn jaw winking is typically monitored indefinitely unless there is cosmetic concern and/or surgical intervention is desired.

Answer 14

Cocaine confirms a diagnosis of Horner's; hydroxyamphetamine will differentiate between pre and post-ganglionic lesions Explanation In patients with a suspected Horner's syndrome, cocaine will confirm the diagnosis, while hydroxyamphetamine will differentiate a pre-ganglionic from a post-ganglionic lesion. A summary of pharmacologic testing in Horner's is summarized below. 10% Cocaine - The normal pupil will dilate, but the abnormal pupil will not - The rationale for this is that in a normal pupil, norepinephrine is released from the post-ganglionic sympathetic nerve endings, which is eventually re-absorbed, terminating the nerve impulse - Cocaine inhibits the re-uptake of norepinephrine, allowing it to accumulate in the synapse, and will cause dilation of the pupil - In Horner's syndrome, the abnormal eye will not produce any norepinephrine in the first place, so cocaine has no effect on the pupil size 1% Hydroxyamphetamine - In a pre-ganglionic lesion, both pupils dilate - In a post-ganglionic lesion, the abnormal pupil will not dilate - The rationale for this is that hydroxyamphetamine will stimulate the release of norepinephrine from the post-ganglionic neurons - If there is damage to a pre-ganglionic neuron (leaving the post-ganglionic intact), norepinephrine will be released, and dilation will occur - If there is damage to the post-ganglionic neuron, hydroxyamphetamine will have no effect on this neuron, no norepinephrine will be released, and the pupil will not dilate

Answer 15

Dura mater, arachnoid, pia mater Explanation The correct order of the optic nerve meninges is the same as those found on the brain which makes sense since they are extensions of each other. The dura mater is the most external layer and is composed of very dense connective tissue. Next is the arachnoid follows next whose connective tissue is less ordered than the dura mater. The most internal of the meninges is the pia mater which is adhered to the nerve.

Answer 16

Inferior rectus Inferior oblique Medial rectus Explanation The medial muscular branch of the ophthalmic artery supplies the medial rectus, inferior rectus, and the inferior oblique extra-ocular muscles, while the lateral muscular branch supplies the superior rectus, superior oblique, lateral rectus, and levator palpebrae superioris.