Optic Nerve/Neuro-ophthalmic Pathways Flashcards
In general, at which location in the eye do axons of the nerve fiber layer become myelinated?
Anterior to the lamina cribrosa
At the equator
Posterior to the lamina cribrosa
Juxtafoveally
Posterior to the lamina cribrosa
Explanation
Axons of the nerve fiber layer generally become myelinated just after they pass posteriorly through the lamina cribrosa. Occasionally, oligodendrites will enter the eye during ebryogenesis causing myelination of the nerve fiber layer. This will appear as a white nerve fiber layer with feathery margins usually extending from the optic disc. In general, axons within the retina should not be myelinated. Myelination of the nerve fiber layer can be associated with amblyopia, strabismus, nystagmus, optic neuritis, neovascularization of the retina and myopia. However, in most cases, individuals that display this condition are asymptomatic.
Which of the following are the MOST common causes of a pupil sparing and pupil involving third nerve palsy, respectively?
Demyelinating disease, compressive lesions
Compressive lesions, demyelinating disease
Microvascular disease, demyelinating disease
Compressive lesions, microvascular disease
Microvascular disease, compressive lesions
Demyelinating disease, microvascular disease
Microvascular disease, compressive lesions
Explanation
The parasympathetic pupillary fibers, along with the surface of the oculomotor nerve, derive their blood supply from the surrounding blood vessels of the pia mater. Conversely, the main trunk of the third nerve is supplied by the vasa nervorum, which courses internally in the nerve. Due to the location of pupillary fibers and the difference in blood supply to the superficial and internal fibers of the oculomotor nerve, certain features that present in cases of third nerve palsies can help differentiate a “surgical” from a “medical” lesion.
Surgical lesions (aneurysms, trauma, uncal herniation) characteristically involve the pupil due to compression of the superficially coursing pupillary fibers and pial blood vessels. These cases are known as “pupil involving third nerve palsies.” Medical lesions (hypertension, diabetes) commonly spare the pupil because these conditions typically involve the vasa nervorum, leading to ischemia of the internal fibers of the oculomotor nerve while sparing the superficial pupillary fibers. This condition is also known as a “pupil-sparing third nerve palsy.”
It is important to note that these principles are not infallible. There are some cases in which pupil involvement is associated with diabetes, and compressive lesions may not initially cause pupil involvement.
The optic nerve is vital for transmission of visual information to the brain. Where does the optic nerve terminate?
At the optic chiasm
At the optic disc
At the visual cortex
At the lateral geniculate nucleus
At the optic chiasm
Explanation
The optic nerve is approximately 50 mm in length and originates at the optic disc which is visible upon examination of the eye with an ophthalmoscope. The optic nerve extends from the globe and terminates at the optic chiasm. At the optic chiasm the nasal fibers cross over contralaterally whereas the temporal fibers remain ipsilateral. The chiasm then gives way to the optic tract which courses to the visual cortex.
The trigeminal nerve has three main divisions. Which of the following corresponds to division 1 of the trigeminal nerve (V1)?
Ophthalmic division Long ciliary Supraorbital Posterior ethmoid Infratrochlear
Ophthalmic division
Explanation
Cranial nerves and their respective divisions can be very confusing and are best understood and remembered with diagrams and mnemonics.
The trigeminal nerve has three main divisions: ophthalmic (V1), maxillary (V2), mandibular (V3).
The ophthalmic division (V1) has three sub-divisions (think NFL) which are the nasociliary, frontal, and lacrimal.
The frontal division of the V1 branch possesses two sub-divisions: the supraorbital and the supratrochlear. The frontal division is the most commonly affected in herpes zoster ophthalmicus.
The nasociliary division has four sub-divisions (think LINE): long ciliary, infratrochlear, nasal, and the posterior ethmoid.
The ophthalmic portion (V1) of cranial nerve V (the trigeminal nerve) possesses three main sub-divisions. Which of the following is a subdivision of V1?
Supratrochlear division
Mandibular division
Maxillary division
Frontal division
Frontal division
Explanation
Cranial nerves and their respective divisions can be very confusing and are best understood and remembered with diagrams and mnemonics.
The trigeminal nerve has three main divisions: ophthalmic (V1), maxillary (V2), mandibular (V3).
The ophthalmic division (V1) has three sub-divisions (think NFL) which are the nasociliary, frontal and lacrimal.
The frontal division of the V1 branch possesses two sub-divisions: the supraorbital and the supratrochlear divisions. The frontal division is the most commonly affected in herpes zoster ophthalmicus.
The nasociliary division has four sub-divisions (think LINE): long ciliary, infratrochlear, nasal, and the posterior ethmoid.
While performing confrontation fields, your patient reports seeing all of your fingers when presented on the left and right side of her visual field exclusively; however when your fingers are presented on both sides simultaneously, the patient only reports seeing the fingers on your left hand (her right visual field). What type of lesion is consistent with these findings?
A lesion in the left parietal lobe A lesion in the right frontal lobe A lesion in the right parietal lobe A lesion in the right occipital lobe A lesion in the left frontal lobe
A lesion in the right parietal lobe
Explanation
This type of finding is consistent with a person who suffers from a right parietal lobe lesion. Remember, the right side of the brain processes info from the left side of the body and visual field. A person who has this type of lesion may also demonstrate visual neglect, meaning that they will ignore the half of their body on the opposite side of the lesion. For example a person with a right parietal lesion will apply make-up to the right side of her face but not the left side. The neglect is much more pronounced if a person is presented with stimuli to both sides of their visual field simultaneously. For this reason it is important to test confrontational fields on both sides of the visual field at the same time in order to manifest a phenomenon called visual/parietal extinction. In this phenomenon, the object presented contralateral to the lesion will not be seen by the patient because it is extinguished by the object presented on the unaffected side. This allows for easier detection of a potential lesion, and it just takes a few more seconds of chair time for the patient.
Which area of the retina naturally corresponds with a sensitivity of 0 decibels on visual field testing?
The macula The optic nerve head The papillomacular bundle The superior arcade The inferior arcade
The optic nerve head
Explanation
The optic nerve head, also known as the blind spot, will demonstrate a sensitivity of 0 decibels, because this area of the eye does not contain any visual receptors, and therefore does not possess any viable vision. The area of the retina with the highest decibel level (hence the highest sensitivity) as seen with visual field testing is the fovea. The sensitivity to stimuli decreases with increasing distance from the fovea.
Which of the following is LEAST likely to result in the observation of an afferent pupillary defect?
Severe, bilateral, asymmetrical macular degeneration
Asymmetric, bilateral, glaucomatous damage with 20/20 acuity in both eyes
A dense unilateral cataract
A patient with a dense corneal scar in one eye and glaucomatous damage in the contralateral eye
A dense unilateral cataract
Explanation
The afferent pathway (the pathway from the eye to the brain) is evaluated by having the patient focus on a distant target under moderate lighting conditions. A bright controlled light source (transilluminator) is then directed from below the patient’s line of sight into the pupil. A normal pupil will quickly constrict and then slowly increase in size until it is mid-dilated, followed by hippus. This procedure is then repeated on the other eye. The light source is then alternated quickly back and forth between the pupils to evaluate the consensual response. Damage to the afferent pathway will cause an afferent pupil defect or light-near dissociation. Light-near dissociation occurs when the pupil response to a near stimulus is greater than the pupil reaction to light.
Afferent pupillary defects are observed if there is retinal or optic nerve damage. However, the damage between the eyes must be asymmetrical in order for an APD to be observed. Even a small amount of nerve damage may cause an APD, whereas a much larger degree of retinal damage is required to produce an APD. As long as the light source used is adequate, a dense cataract or a corneal scar should (in theory) not cause an APD.
A patient with bilateral tilted discs whose crescents are inferior and nasally displaced will typically display a defect located along which portion of the visual field test?
Inferior nasal
Superior temporal
Inferior temporal
Superior nasal
Superior temporal
Explanation
A patient who has tilted discs will have an optic nerve that exits the eye superiorly, and may be accompanied by situs inversus, fundus ectasia, myopia, and superior temporal visual field defects that do not generally respect the midline. Sometimes the visual field defects can appear similar to those of a person who suffers from a pituitary tumor. It is important to distinguish between the two and this situation requires further evaluation.
The FIRST synapse in the visual pathway occurs in which of the following layers of the retina?
Photoreceptor layer Inner plexiform layer Outer plexiform layer Ganglion cell layer Inner nuclear layer Outer nuclear layer
Outer plexiform layer
Explanation
The first synapse of the visual system occurs in the outer plexiform layer (OPL) of the retina. It is here that the cone pedicles and rod spherules are synaptic upon the dendrites of various bipolar cells. Additionally, projections from horizontal cells also make contact with rods, cones, and bipolar cells in the outer plexiform layers.
Visual acuity can be used to assess the function of which cranial nerve?
II VI VI IV III
II
Explanation
Visual acuity, along with confrontation fields, pupil reflex evaluation, and the red cap desaturation test, can be utilized to assess the integrity of cranial nerve II (optic). Cranial nerves III (oculomotor), IV (trochlear), and VI (abducens) can be evaluated via extraocular motility (versions). Cranial nerve V (trigeminal) is measured via facial stimulation (forehead, nose, and jawline to assess all three divisions), corneal sensitivity, and palpation of the masseter muscles while the patient clenches their teeth.
Damage to the left trochlear nucleus will affect which of the following muscles?
The right superior rectus The right superior oblique The left superior oblique The left medial rectus The left superior rectus
The right superior oblique
Explanation
Fibers of the trochlear nerve decussate, and therefore innervate, the CONTRALATERAL superior oblique muscle. The superior oblique is responsible for incyclotorsion, depression, and abduction. Cranial nerve (CN) IV is unique in that it travels the longest intracranial course when compared to all of the other cranial nerves. The trochlear nerve is also the smallest cranial nerve, and because this nerve is so thin it is prone to damage. A CN IV palsy will cause a hypertropia of the eye on the affected side and the patient will report vertical diplopia that is worse in downgaze and at near.
Which of the following ocular conditions will NEVER produce a relative afferent pupillary defect in the ipsilateral eye?
Optic nerve glioma Central retinal artery occlusion Optic neuritis Mature cataract Total retinal detachment
Mature cataract
Explanation
A relative afferent pupillary defect (RAPD) occurs in patients who have a history of an incomplete optic nerve lesion (a complete lesion would result in an absolute afferent pupillary defect), or the presence of severe retinal disease. The clinical features of a relative afferent pupillary defect include a pupil that responds weakly to light stimulation in the diseased eye and briskly to light stimulation in the normal eye. The results are exaggerated during the swinging flashlight test, in which both eyes will constrict when the normal eye is presented with a light stimulus, and both eyes will slowly dilate when the diseased eye is presented with the same amount of light. This anomalous result of dilation of the pupils in response to light occurs because the normal dilation that occurs when the light is withdrawn from the normal eye is more pronounced than the constriction that is produced by stimulating the abnormal eye.
There are several conditions that may cause an afferent pupillary defect. These include severe retinal diseases, or macular scarring, severe asymmetric glaucoma, an optic nerve glioma or meningioma, central retinal artery occlusion or ischemic central retinal vein occlusion, optic neuritis, or any lesion that occurs along any segment of the optic nerve, usually prior to the chiasm. A dense cataract will never cause a relative afferent pupillary defect in the same eye, and should, therefore, never be used to explain the presence of an RAPD.
Which space in the meninges of the optic nerve is continuous with the space between the brain meninges such that an increase in cerebrospinal fluid pressure may cause the appearance of papilledema?
The subdural space
Subarachnoid space
Dural sinuses
The subpial space
Subarachnoid space
Explanation
The subarachnoid space of the optic nerve is continuous with that of the brain. The subarachnoid space exists between the arachnoid and the pia mater and ends at the lamina cribrosa where it folds back on itself and terminates in a cul-de-sac. This space is filled with cerebrospinal fluid (CSF) and therefore should anything cause an increase in CSF pressure, this can translate down to the nerve and manifest as papilledema.
The dural sinuses are venous channels that carry blood from the brain to the heart, not cerebrospinal fluid.
The dura is generally firmly attached to the skull or bones and the arachnoid is connected to the dura. In the event of injury, trauma or sickness the dura and arachnoid may become separated resulting in a space called the subdural space.
In a healthy individual there should not exist a space underneath the pia mater. The pia mater is an extremely thin membrane that adheres very closely to the brain, spinal cord and optic nerve such that it follows the sulci and gyri of the brain’s surface.
Which of the following BEST describes the rotation of the eyeball during Bell’s phenomenon?
Upward and outward
Downward and outward
Upward and inward
Downward and inward
Upward and outward
Explanation
Bell’s phenomenon is a reflex coordinated between the facial nerve and the oculomotor nuclei in which the eyeball is rotated upward and outward upon closure of the eyelids. The reflexive movement occurs as a protective mechanism that repositions the cornea up under the eyelid and, therefore, away from potential danger. The neurological pathway of this phenomenon is not completely understood. It is also not present in about 10% of otherwise healthy individuals; thus, its absence cannot be relied upon as a cause or cited as a sign of disease.
Ocular perfusion pressure (OPP) is defined as which of the following?
Systemic blood pressure minus episcleral venous pressure
Systemic blood pressure minus intraocular pressure
Systolic blood pressure minus diastolic blood pressure
Episcleral venous pressure minus intraocular pressure
Systemic blood pressure minus intraocular pressure
Explanation
Ocular perfusion pressure (OPP) is defined as systemic blood pressure minus intraocular pressure (IOP). OPP is important in that many researchers believe that it potentially plays a role in the pathophysiology of glaucoma; although this remains controversial. Some believe that low OPP results in decreased perfusion of ocular tissues, which may contribute to hypoxia or ischemia of optic nerve tissue.
