Flashcards in BCSC Neuro-Op Deck (314):
What is the pattern deviation plot of a visual field?
It reports the analysis of sensitivity values based on age-expected values for all points tested after shifting (by the 7th highest point). This helps account for media opacities, although optic neuropathy may also cause total deviation depression without pattern deviation abnormalities.
What is the false-positive rate for a visual field?
frequency of patient signalling light when no light is displayed
What is the false-negative rate for a visual field?
Frequency of patient failing to signal when a target brighter than the previously determined threshold for the same spot is displayed
What are fixation losses on a visual field?
the frequency with which the patient signals seeing a light when it is presented in the physiologic blind spot (e.g., 4 signals out of 21 times presented)
What are the two types of contrast sensitivity tests?
Grating tests (give contrast threshold vs. spatial frequency function) and Letter tests
Can contrast sensitivity be diminished in the absence of visual acuity decrease?
Is contrast sensitivity testing specific for optic nerve dysfunction?
How does photostress recovery testing differentiate between optic neuropathy and other etiologies of decreased vision?
Patients with optic neuropathy demonstrate normal recovery times (30 seconds) from photostress (bright light fixation for 10 seconds), while patients with maculopathy or ischemia show slowed recovery from photostress (90-180 seconds)
What is done in PAM (Potential Acuity Meter) testing?
Optotypes are projected onto the retina through a dilated pupil, providing an estimate of best potential visual acuity
How can true edema and pseudoedema of the optic disc be differentiated?
On FA, a truly swollen disc will leak, while pseudoedema (as in LHON) will not leak
What type of light source does OCT use?
What is visual evoked potential recording?
Electrical signals produced in response to a visual stimulus are measured via electrodes placed on the scalp overlying the occipital cortex
In which situations is VEP particularly helpful?
1) Patient unable to communicate, 2) confirmation of intact visual pathways in patient with suspected non-organic disease
What does electroretinogram (ERG) measure?
The electrical activity of the retina in response to various light stimuli under different states of light adaptation.
How is electrical activity measured for an ERG?
With electrodes embedded in a corneal contact lens worn for testing
What are the major components of the electrical waveform generated by ERG?
a-wave (photoreceptors), b-wave (inner retina: Muller and ON-bipolar cells), c-wave (RPE, photoreceptors)
What are the 3 forms of ERG?
Full-field ERG, Pattern ERG, and Multi-focal ERG
Is the multifocal ERG signal usually normal or abnormal in optic nerve disease?
What are common maculopathies and retinopathies that can present similarly to optic neuropathy?
1) Acute Idiopathic Blind-Spot enlargement, 2) MEWDS, 3) Cone Dystrophy, 4) Vitamin A deficiency, 5) Hydroxychloroquine and chloroquine retinopathy, 6) Cancer-associated retinopathy, 7) Melanoma-associated retinopathy
With what findings do patients with optic neuropathies present?
visual acuity loss, visual field loss, dyschromatopsia, RAPD
What are the 3 major groups of ganglion cell nerve fibers entering the optic nerve?
1) Papillomacular fibers, 2) Arcuate fibers, 3) Nasal radiating fibers
What types of scotomata result from damage to the papillomacular fibers?
1) cecocentral scotoma, 2) paracentral scotoma, 3) central scotoma
What types of scotomata result from damage to the arcuate fibers?
1) altitudinal defect, 2) nasal step defect
What types of scotomata result from damage to the nasal radiating fibers?
1) temporal wedge defect
What is a cecocentral scotoma?
A scotoma that extends from central vision temporally to the natural blind spot
How does blind spot enlargement result from optic disc edema?
Displacement of the peripapillary retina
Where does early papilledema begin?
at the superior and inferior poles of the optic disc
What is papilledema?
edema of the optic nerve head that results (specifically) from increased intracranial pressure (ICP)
What are the primary findings of acute papilledema?
1) hyperemia of the optic disc, 2) dilation of disc surface capillary net, 3) telangiectasia of surface and radial peripapillary vessels, 4) grayish, feathered NFL obscuring disc edge and peripapillary retinal vessels
What are features suggestive of true disc edema?
1) hyperemia, 2) microvascular abnormalities of the disc surface, 3) opacification of peripapillary NFL
What is the most common cause of pseudopapilledema?
optic disc drusen
What are conditions that can mimic papilledema?
1) optic disc drusen, 2) hyaloid remnants on disc surface, 3) glial tissue on disc surface, 4) congenital appearance, 5) vitreopapillary traction, 6) NFL myelination
What are causes of papilledema (i.e. increased ICP -> disc edema)?
intracranial mass, hydrocephalus, CNS infection, infiltration by inflammatory or neoplastic process, cerebral venous thrombosis, pseudotumor cerebri
Should neuroimaging be obtained urgently in suspected papilledema?
What portion of the disc is last to become blurred/edematous in acute papilledema?
the temporal portion
Is the absence of spontaneous venous pulsations useful in assessing for papilledema?
Only if they were known to be visible previously, as this is a physiologic variant in 20% of individuals
What findings are seen in chronic papilledema?
1) pale optic disc, 2) gliosis of peripapillary NFL, 3) optociliary shunt vessels due to chronic CRV obstruction, 4) refractile bodies of the disc
Do most patients with IIH have papilledema?
What are symptoms associated with IIH?
Headache, nuasea, transient visual obscurations, diplopia (2/2 abducens paresis), visual field loss, pulse synchronous bruit
What are associations/possible etiologies of IIH?
vitamin A (>100,000 U/day), tetracycline, minocycline, doxycycline, retinoic acid, lithium, sleep apnea
What medical therapies can be used for IIH aside from analgesics?
acetazolamide and topiramate (furosemide or IV steroids second-line)
What are surgical therapies for IIH?
optic nerve sheath fenestration (ONSF) or CSF diversion procedure (VP or LP shunt)
Does headache improve after optic nerve sheath fenestration?
No, ONSF does not change ICP
What is the presentation of Anterior Ischemic Optic Neuropathy (AION)?
Painless monocular vision loss developing over hours to days, visual field loss (often altiduinal or arcuate), RAPD, optic disc edema in patients usually > 50 yo
What are the two classifications of AION?
Arteritic AION (AAION) and Non-arteritic AION (NAION)
What are indications that a patient has AAION rather than NAION?
1) chalky white disc edema (vs. hyperemic), 2) cotton wool spots away from optic disc (vs. adjacent to disc), 3) delayed choroidal filling (vs. normal), 4) normal or large cup in fellow eye (vs. small)
What is the cause of AAION?
AAION is caused by inflamatory and thrombotic occlusion of the short posterior ciliary arteries
What is the most common cause of AAION?
GCA, which results in headache, scalp tenderness, anorexia, weight loss, fever, jaw claudication
What is occult GCA?
GCA with elevated ESR but no systemic symptoms or with normal ESR and systemic symptoms. It occurs in 20% of AAION patients.
What percent of AION is AAION?
only 5%-10% of AION is AAION
Are patients with AAION usually older or younger than NAION patients?
AAION patients are older
What is the immediate management of suspected AAION?
IV steroids (methylprednisolone 1g/day for first 3-5 days, followed by prednisone 1mg/kg/day tapered over 3-12 monhts) + daily aspirin. Temporal artery biopsy may be delayed up to 10 days without compromise of results
What is the primary goal of AAION therapy?
To prevent contralateral vision loss (which occurs in 95% of cases within days to weeks if untreated)
What is the presumed etiology of NAION?
compromised optic disc microcirculation with structural "crowding" of the disc
To what does the term "disc at risk" refer?
Refers to the optic disc in the contralateral eye in NAION, which typically has a small diameter and small or absent physicologic cup
What are the characteristic findings in Foster Kennedy and pseudo-Foster Kennedy syndrome?
One optic disc is atrophic, while the other is edematous. Atrophic disc indicates chronic injury while edematous disc indicates recent or ongoing injury.
What is the difference between Foster Kennedy and pseudo-Foster Kennedy syndrome?
Only the etiology of the findings. NAION (prior occurrence in one eye, new recurrence in contralateral) --> pseudo-FK; intracranial mass (chronic compression of one nerve, increased ICP causing edema of other) --> FK.
What percent of AION is NAION?
What are risk factors for NAION?
Structural crowding of optic cup, systemic hypertension, DM, hyperlipidemia
What condition is important to rule out when suspecting NAION?
optic neuritis, which is indicated by optic nerve enhancement with gadolinium on MRI
Does vision improve after NAION?
It can, by 3 lines in 31% of patients after 2 years
Do therapies exist for NAION?
No proven therapy exists. ONSF does not work per Ischemic Optic Neuropathy Decompression Trial (IONDT).
What is the appearance of the optic disc in optic neuritis?
Normal in 2/3 of cases, edematous in 1/3
What are the 3 common types of optic neuritis?
Postviral, infectious, and demyelinating (MS)
What are the clinical characteristics of neuroretinitis?
Acute loss of vision with disc edema and a star pattern of exudates in the macula
Do patients with neuroretinitis have an increased risk of MS?
What is the most common cause of neuroretinitis?
Cat-scratch disease (caused by Bartonella henselae or Bartonella quintana)
What are characteristic findings in diabetic papillopathy?
Hyperemic edema of disc, dilatino of disc surface microvasculare difficult to distinguish from NVD
What is papillophlebitis?
A subset of CRVO in the young, with unusually prominent disc edema, normal acuity pupils, and color vision, and blind spot enlargement
What is the natural history of papillophlebitis?
It will usually resolve spontaneously over 6-12 months, with minimal visual loss
What is the predominant theory regarding the etiology of optic disc drusen?
impaired ganglion cell axonal transport, possibly related to a small scleral canal and mechanical obstruction
Do most patients with optic disc drusen experience symptoms?
No, most patients with optic disc drusen do not experience symptoms (>90%). 8.6% may experience transient visual obscurations.
What methods can be used to identify optic disc drusen (and differentiate it from papilledema)?
1) B-scan ultrasound (highly reflective), 2) FA (autofluorescence, no leakage), 3) CT, 4) OCT
From which conditions must optic disc drusen be differentiated?
1) Papilledema, 2) Astrocytic hamartoma of the retina (2/2 tuberous sclerosis or neurofibromatosis)
What are two ways in which to differentiate astrocytic hamartomas from optic disc drusen?
1) Astrocytic hamartomas do not autofluoresce (unlike ODD), and 2) Astrocytic hamartomas typically obscure the retinal vessels (unlike the deeper ODD)
What demographic is most often affected by Leber hereditary optic neuropathy?
Males 10-30 years old
What is the clinical presentation of LHON?
acute, severe, painless, vision loss (<20/200), central or cecocentral visual field impairment
What are the fundus findings in LHON?
1) hyperemia and elevation of the optic disc with pseudoedema (no leakage on FA), 2) peripapillary telangienctasia, 3) tortuosity of medium-sized retinal arterioles
What is the etiology of LHON?
Mutation in mitochondrial DNA (three known mutations can lead to the disease)
Does visual recovery occur after LHON?
rarely; more common with the 14484 mutation
Does a proven therapy exist for LHON?
Not presently, although in vitro studies suggest estrogen may have a protective effect
What is the gene thought to cause autosomal dominant optic atrophy (ADOA)?
OPA1 gene on chromosome 3
Where does focal notching of the optic disc usually occurin chronic open-angle glaucoma?
inferior or superior pole
What is the usual size of the optic disc in optic nerve hypoplasia?
Small, disc diameter is 1/2 to 1/3 the diameter of a normal disc
What syndrome involving optic nerve hypoplasia is most common?
Septo-optic dysplasia (ONH, absent septum pellucidum, pituitary dwarfism)
What are common associations of ONH?
midline or hemispheric brain defects, endorcrinologic abnormalities, congenital suprasellar tumors
What percent of patients with congenital tilted disc syndrome have bilateral involvement?
Where is the colobomatous excavation of the optic nerve tissue in Congenital Tilted Disc Syndrome?
inferonasal optic disc
What conditions are included in the spectrum of Excavated Optic Disc anomalies?
1) Optic pit, 2) Coloboma, 3) Dysplastic nerve, 4) Morning glory disc
What is an optic pit?
a depression of the optic disc surface located inferotemporally, associated with mild visual field defect (paracentral or arcuate), and possible serous detachment of macula
From what do optic nerve colobomas result?
incomplete closure of the embryonic fissure, usually inferiorly
What is the morning glory disc anomaly?
a funnel-shaped staphylomatous excavation of the optic nerve and peripapillary retina. Retinal vessels characteristically emanate from the periphery of the disc.
Is neuroimaging warranted in a patient with morning glory disc anomaly?
Yes, the patient may have a basal encephalocele or CNS vascular anomalies.
What are the characteristics of retrobulbar optic neuritis?
Subacute, monocular vision loss developing over several days, accompanied by periorbital pain, RAPD, red dyschromatopsia in a young (32yo) female (77%) patient.
When does vision recovery usually occur in retrobulbar optic neuritis?
Within 1 month
Did the Optic Neuritis Treatment Trial (ONTT) demonstrate any long-term vision benefit of corticosteroids for optic neuritis?
No. They did not improve visual outcome, but IV steroids did speed time to recovery by 1-2 weeks.
Is treatment of retrobulbar optic neuritis with IV steroids appropriate?
If pateint requires rapid return of vision (e.g. is monocular), then yes. Otherwise, no, given the potential for complications and lack of long-term benefit.
What are the diagnostic criteria for neuromyelitis optica?
1) optic neuritis, 2) myelitis, 3) 2 of a) spinal cord lesion involving 3+ vertebral segments, b) MRI nondiagnostic for MS, c) positive NMO-IgG serology
When should testing for NMO-IgG be considered?
1) progressive vision loss for >2 weeks, 2) lack of vision improvement by 1 month, 3) recurrent optic neuritis
What is optic perineuritis?
Inflammation of the optic nerve sheath
Does optic perineuritis respond to steroids?
Yes, immediately and dramatically
What are the two means by which optic nerve dysfunction can occur in thyroid eye disease (TED)?
1) EOM enlargement leading to compression of the optic nerve, 2) stretching of the optic nerve 2/2 proptosis
With what do intraorbital and intracanalicular compressive optic neuropathy present?
slow progressive vision loss, RAPD, monocular field loss
What are the two most common types of primary optic nerve tumors?
1) optic nerve glioma, 2) optic nerve sheath meningioma
What is the diagnostic triad of the optic nerve sheath meningioma (ONSM)?
1) painless, slowly progressive monocular vision loss, 2) optic atrophy, 3) optociliary shunt vessels
What are optociliary shunt vessels?
Preexisting optic disc channels that dilate in response to chronic obstruction of outflow through the central retinal vein. Optociliary shunt vessels shunt retinal venous outflow to the choroidal circulation and would be more accurately called "retinochoroidal collaterals"
What is the treatment of choice for optic nerve sheath meningioma?
Fractionated radiation therapy (produces stability or vision improvement in up to 94.3% of patients)
Where are optic pathway gliomas (OPGs) found?
Involving the optic nerve, the optic chiasm, or both
What percent of OPGs are detected by the first and second decades of life?
70% and 90%, respectively
Is biopsy of OPGs usually recommended?
No, may cause additional vision loss and high-resolution neuroimaging provides sufficient diagnostic accuracy
What are the two classifications of malignant optic nerve gliomas?
Anaplastic astrocytomas or glioblastoma multiforme
What is the usual clinical presentation of toxic or nutritional optic neuropathy?
gradual, progressive, painless vision loss that is bilateral and symmetric
What are two exceptions to the typically gradual vision loss seen in toxic optic neuropathies?
Methanol toxicity and Ethylene glycol toxicity both produce rapid vision loss
What are the most commonly implicated medications in toxic optic neuropathy?
1) ethambutol, 2) linezolid, 3) isoniazid, 4) chloramphenicol, 5) hydroxyquinolines, 6) penicillamine, 7) cisplatin, 8) vincristine, 9) lead ingestion
What is the time to development of optic atrophy after optic nerve trauma?
What is the clinical characterization of Posterior Ischemic Optic Neuropathy (PION)?
Ischemic damage to the retrobulbar portion of the optic nerve results in abrupt, severe vision loss, RAPD, with initially normal-appearing discs.
What are the 3 clinical scenarios in which PION occurs?
1) perioperative, 2) arteritic (esp. GCA), 3) non-arteritic
What is the prognosis for vision recovery in PION?
What is the most common clinical scenario in which PION occurs?
Perioperative scenario, particularly those involving substantial blood loss, hypotension, or prolonged anesthesia duration.
What are the most common causes of infiltrative optic neuropathy?
1) leukemia, 2) lymphoma, 3) granulomatous inflammation (sarcoid, syphilis, TB, fungal infection
How should cases of suspected infiltrative optic neuropathy be evaluated initially?
1) MRI brain and orbits with fat suppression and gadolinium contrast, 2) screening tests for myeloproliferative, inflammatory, and infectious disorders that are common causes (see other questions), 3) LP with CSF analysis (may need to be repeated, as sensitivity of single test is low)
What is the median survival time for meningeal carcinomatosis?
4-9 weeks, even with aggressive therapy
What percent of isolated optic atrophy without clear cause is due to a compressive lesion?
Where are nasal and temporal retinal fibers segregated?
At the optic chiasm
What is a junctional scotoma?
A field loss due to injury of an optic nerve at its junction with the optic chiasm. It is characterized by 1) Diminished visual acuity and central visual field loss in the ipsilateral eye and 2) temporal hemianopia in the contralateral eye
What is the most common visual field defecct of chiasmal compression?
Is the pituitary inferior or superior to the optic chiasm?
Are hormonally active pituitary tumors usually identified before or after vision loss?
What is pituitary apoplexy?
The sudden hemorrhage of or impaired perfusion of the pituitary gland, usually due to hemorrhage or infarction of a pituitary tumor. Expansion of the hemorrhage/tumor can cause vision loss by optic chiasm compression as well as CN II, IV, V, and VI dysfunction through extension into cavernous sinuses.
What are three causes of bitemporal vision loss other than pituitary adenoma?
1) Parasellar meningioma and 2) Craniopharyngioma (usually inferior bitemporal visual field loss), 3) significant closed-head trauma injuring the chiasm
What are possible therapies for parasellar tumors?
1) observation if fields are normal, 2) surgery (transfrontal or transsphenoidal), 3) medication, 4) radiation
Does vision loss improve after resection of parasellar tumors?
Yes, it is often rapid and dramatic, as long as retinal nerve fiber layer (RNFL) thickness remains greater than 75 microns
Injuries at which points in the optic pathway must respect the vertical midline?
At and posterior to the optic chiasm
What are the most common causes of homonymous hemianopias, in order of decreasing incidence?
1) Stroke, 2) TBI, 3) tumor
What are the components of the Optic Tract Syndrome?
1) Homonymous hemianopia, 2) Bow-tie optic atrophy of contralateral optic disc, 3) Mild RAPD in contralateral eye (more crossed than uncrossed fibers in optic tract)
After what part of the optic pathway does visual information enter the LGN?
After the optic tract
Occlusions of which two arteries each lead to homonymous sectoranopias respecting the vertical midline due to impaired perfusion of the Lateral Geniculate Nucleus (LGN)?
1) Lateral posterior choroidal artery (central wedge; branch of Posterior Cerebral Artery), 2) Anterior choroidal artery (upper and lower wedge; branch of MCA)
Where do fibers of the superior visual field course?
Primarily through the Meyer Loop of the Temporal Lobe
What field deficit does damage to the Meyer loop produce?
Superior, incongruous, homonymous defects sparing fixation contralateral to side of lesion
What visual field defect do lesions to the visual fibers passing through the parietal lobe produce?
contralateral inferior homonymous hemianopia
What function do the excess crossed fibers reaching the visual cortex serve?
They produce a monocular "temporal crescent" of visual field in the far periphery (60-90 degrees)
What horizontal fissure runs through the visual cortex in the occipital lobe?
The calcarine fissure
What are the 4 primary types of visual field deficits that can be seen with occipital lobe lesions?
1) congruous homonymous hemianopia, possibly sparing fixation region (PCA stroke), 2) monocular defect of temporal crescent, 3) homonymous defect sparing temporal crescent in eye contralateral to lesion, 4) homonymous hemianopia respecting both vertical and horizontal midline
In which situations is a watershed (dual arterial supply) area 1) at risk and 2) protected?
1) at risk in systemic hypoperfusion, 2) protected in stroke involving one of the arterial supplies
Why is the macula spared in PCA strokes?
The portion of the visual cortex receiving input from the macula is the tip of the occipital cortex and receives arterial supply from both the PCA and the MCA.
Are pupillary responses affected in cortical blindness?
What is Riddoch phenomenon?
Inability to perceive static targets, while maintaining ability to perceive moving targets. Can be seen in patients with occipital lobe injury.
What duration of vision loss is considered "transient"
less than 24 hours
What is the most common cause of transient monocular vision loss (TMVL)?
Carotid artery disease
What is the most common cause of transient binocular vision loss (TBVL)?
What are the key points to ascertain in evaluating a patient with transient vision loss?
1) Monocular vs. Binocular, 2) Age, 3) Duration, 4) Pattern of visual loss/recovery, 5) Associated signs/symptoms
What is the usual duration of transient visual loss in patients with TIA?
minutes (up to 15 minutes)
What is the usual duration of transient visual loss in patients with migraine?
What is the Uhthoff phenomenon?
Transient visual blurring with physcial activity or elevation in body temperature. It frequently occurs in patients with current of previous optic neuritis.
What does gaze-evoked visual loss suggest?
Orbital mass such as hemangioma or meningioma (likely due to positional vascular obstruction)
What are the three most common types of emboli to the retinal circulation/
1) cholesterol, 2) platelet-fibrin, 3) calcium
What are cardiac causes of retinal emboli?
1) ventricular aneurysms, 2) hypokinetic wall segments, 3) endocarditis, 4) valvular heart disease (MVP or atrial myxoma), 5) arrhythmia, 6) PFO
What medical therapies should be implemented for a patient who has expereinced a retinal TIA?
1) anti-platelet therapy (aspirin, aspirin-dipyridamole, clopidogrel, or cilostazol), 2) statin, 3) consider ACE inhibitor
What tests should be performed in a patient with suspected GCA?
ESR, CRP, platelet count
What are findings in ocular ischemic syndrome?
retinal venous dilation, midperipheral dot-and-blot hemorrhages, optic disc edema, retinal artery narrowing with microaneurysm formation
How does vasospasm of the retinal artery usually present?
In patients < 50 years old, with family history of migraine, stereotypic episodes of painless TMVL
What workup should be performed on patients with suspected retinal artery vasospasm?
retinal artery vasospasm is a diagnosis of exclusion, so perform CBC, cardiac evaluation, carotid imaging. Also consider hypercoagulability testing.
What are common causes of transient binocular visual loss?
1) Migraine, 2) occipital mass lesion, 3) occipital ischemia, 4) occipital seizure
What symptom do occipital seizures typically produce in addition to transient binocular visual loss?
Unformed positive visual phenomena (e.g., swirling lights or whiting out of vision)
What is the difference between an illusion and a hallucination?
Illusion refers to false perception of visual information that is present, while hallucination refers to perception of visual information is not actually present
What is the difference between formed and unformed hallucinations?
Formed hallucinations are whole objects, while unformed hallucinations are not (e.g., lights, spots, patterns)
What are photisms?
sensations of color or light induced by a stimulus to a non-visual sense (e.g., sound)
What is palinopsia?
Preservation of visual perception after removal of the original stimulus (multiple afterimages)
Where do lesions usually result in formed visual hallucinations?
Temporal lobe (affecting the anterior optic radiations)
Where do lesions usually result in unformed visual hallucinations?
Parietal and occipital cortices
What is Charles Bonnet syndrome?
Wide-ranging visual hallucinations in visually impaired but cognitively normal individuals
What are three types of disorders of higher cortical function affecting vision?
1) Disorders of recognition, 2) Disorders of Visual-Spatial relationships, 3) Disorders of awareness of vision
Damage to which visual area results in isolated loss of perception of visual motion (akinetopsia)?
V5 (also called MT)
What is cerebral achromatopsia?
Abnormal color discrimination with bilateral inferior occipitotemporal lobe lesions
What is simultagnosia?
Failure to integrate multiple elements of a scene to form the total picture
What is Balint syndrome?
Bilateral occipitoparietal lesions leading to 1) simultagnosia, 2) optic ataxia (disconnection between visual input and motor system), 3) acquired oculor motor apraxia (loss of voluntary movement of the eyes while fixating on a target)
What is visual allesthesia?
perceiving the environment to be rotated, flipped, or inverted
What is Anton syndrome?
denial (or lack of awareness) of blindness (usually cortical blindness)
What is blindsight?
Unconscious rudimentary visual perception in a cortically blind patient
What is hemineglect?
Failure to acknowledge seeing objects in an area of vision known to be intact
Why is the distinction between the supranuclear and infranuclear pathways of the ocular motor system important?
Supranuclear disorders generally affect both eyes similarly, while infranuclear disorders affect the eyes differently
What are the components of the supranuclear pathways of ocular motor control?
1) premotor and motor regions of the frontal and parietal cortices, 2) cerebellum, 3) basal ganglia, 4) superior colliculi, 5) thalamus (LGN and pulvinar), 6) brainstem (PPRF, neural integrators, vestibular nuclei)
What are the components of the infranuclear pathways of ocular motor control?
1) ocular motor nuclei, 2) intramedullary segments of the ocular motor nerves, 3) peripheral segments of the ocular motor nerves, 4) neuromuscular junction, 5) extraocular muscles
What are the 6 ocular motor tracking systems?
1) microsaccadic refixation movements, 2) saccades, 3) optokinetic, 4) smooth pursuit, 5) vergence, 6) vestibular (VOR)
What is the most basic test of ocular stability?
Observation of patient's ability to fixate on a target when the head and body are held stationary
What is the most frequent cause of spontaneous nystagmus?
Imbalance of vestibular input to the ocular motor nuclei
What function does the VOR serve?
It holds images stably on the retina during brief, high-frequency rotations of the head
What sensors provide the basis for VOR movements?
semicircular canals for angular acceleration and otoliths of utricle and saccule for linear acceleration
What is VOR gain?
the ratio of the amplittude of eye rotation to the amplitude of head rotation
What is dynamic visual acuity?
measuring visual acuity during head rotations
What function does the optokinetic nystagmus (OKN) system serve?
The OKN system maintains steady alignment of images on the retina during sustained rotation of the head (or environment)
What is the OKN response?
an initial pursuit movement, followed by a contraversive, corrective involuntary saccade (mediated by the same neurons that respond to vestibular stimulation)
What function does the Saccadic System serve?
The saccadic system rapidly shifts the fovea to targets of interest.
What are saccades?
Ballistic movements that generally cannot be altered once initiated
What is the maximum saccadic velocity?
500 degrees/second (which gives only 0.2 seconds from primary to farthest part of temporal field)
What area controls volitional saccades?
the Frontal Eye Fields (FEF) control volitional saccades, with input from premotor areas)
Is a hypometric saccade usually pathologic?
No, but a hypermetric (overshooting) saccade usually is pathologic.
How can saccades be tested clinically?
Have the patient rapidly shift gaze between 2 targets (e.g. index fingers of clinician on either side of patient's head). Observe the latency, accuracy, velocity, and conjugacy of the movements.
What function does the Pursuit System serve?
The pursuit system permits clear vision by maintaining foveation on a moving target and similarly provides foveal alignment when a person is moving through the environment (any relative motion).
Which areas control pursuit movements?
FEF, middle temporal (MT), medial superior temporal (MST), and posterior parietal cortex
What is the dorsal visual stream?
A visual pathway including visual areas MT and MST that plays a role in detecting moving visual stimuli
How can pursuit movements be tested?
Have the patient follow a predictably moving target horizontally and then vertically while the head and body are held still. The clinician holding up a finger and rocking back and forth is an appropriate stimulus (moving < 30 degrees/second)
What function do vergence eye movements serve?
Vergence eye movements drive the eyes in opposite directions to maintain the image of an object on the fovea of both eyes as the object moves toward or away from the observer.
What are saccadic intrusions?
Rapid, small amplitude eye movements that disrupt stable ocular fixation
What are square-wave jerks (SWJs)?
a type of saccadic intrusion in which the eyes move off of and then back onto a target with symmetric movements. They are common in patients with progressive supranuclear palsy (PSP)
What is an ocular tilt reaction?
a combined head tilt, skew deviation, and cyclotorsional rotation of the eyes to compensate for an apparent tilt of the environment due to peripheral vestibular disease (esp. the otolithic organs)
What is the lateral medullary syndrome (Wallenburg syndrome)?
A stroke syndrome involving the caudal brainstem (lower pons and medulla). Patients present with 1) ipsilateral loss of facial pain and temp sensation, 2) contralateral loss of body pain and temp sensation, 3) ipsilateral cerebellar ataxia, 4) ipsilateral first-order Horner syndrome, 5) ocular tilt reaction
What does impaired VOR suppression (as should occur when fixating on an object that moves with the head) indicate?
cerebellar disease (it is very common in MS)
What type of misalignment (comitant or incomitant) is usually present in congenital strabismus?
Does Maddox rod testing dissociate the two eyes?
What are the most common causes of restrictive strabismus?
Thyroid eye disease and orbital trauma
Do paretic conditions reduce saccade velocity?
Do restrictive conditions reduce saccade velocity?
What are two ways to test for restriction of ocular movements?
Forced ductions and measuring intraocular pressure in both primary position and eccentric gaze
What amount of change in intraocular pressure in upgaze (vs. primary position) indicates the possibility of ocular restriction?
What is suppression?
An adaptation that reduces the responsiveness of the visual neurons in the occipital cortex to the input from one eye
What are supranuclear ocular motor lesions that can produce strabismus and diplopia?
1) alternating skew deviation, 2) convergence insufficiency or spasm, 3) divergence insufficiency, 4) ocular tilt reaction, 5) skew deviation, 6) thalamic esodeviation
What is skew deviation?
An acquired vertical misalignment of the eyes resulting from asymmetric disruption of supranuclear input from the otolithic organs
What is alternating skew deviation on lateral gaze?
An alternating skew deviation on lateral gaze manifests as a hypertropia of the abducting eye that switches when gaze is directed to the opposite side
What is thalamic esodeviation?
an acquired horizontal strabismus that may be observed in patients with lesions near the junction of the diencephalon and the midbrain (most often in thalamic hemorrhage)
What are the subnuclei contained within the third nerve nucleus?
4 nuclei (on either side) for the EOMs innervated by CN III, one nucleus for both the levator muscles (central caudal nucleus), and paired nuclei for the pupillary constrictor muscles (EW nuclei)
What is meant by the term "internuclear" when discussing eye movement control?
Internuclear, as in internuclear lesions, refers to disruptions of the medial longitudinal fasciculus (MLF), a bundle of fibers that connects the 6th nerve nucleus one one side of the pons to the medial rectus (within CN III nucleus) nucleus in the contralateral midbrain
What is the cardinal sign of a unilteral INO?
Slowed adducting saccadic veloocity in one eye
For which side is a unilateral INO named?
The side with impaired adduction (i.e., the side receiving input from a disrupted MLF). This means that a right INO involves impaired adduction of the right eye. Input from CN VI nucleus on the left is not properly received by the right CN III nucleus and the right medial rectus.
Is limited range of adducting movement always seen in an INO?
No, a patient with slowed adduction due to INO may have full or limited range of adducting movement.
What findings are seen in a bilateral INO?
1) bilateral adduction lag, 2) bilateral abducting nystagmus, 3) vertical, gaze-evoked nystagmus (best appreciated in upgaze)
What is the cause of vertical gaze evoked nystagmus seen bilateral INO?
Disruption of vertical vestibular pursuit and gaze-holding pathways, which ascend from the vestibular nuclei through the MLF
What are the two most common causes of INO?
Demyelination (younger) and stroke (older)
What is a "One and a half" syndrome?
The result of an injury to the pons large enough to involve both the MLF and the PPRF (or 6th nerve nucleus) all on the same side of the brainstem. The 6th nerve nucleus injury impairs horizontal gaze toward the ipsilateral side. The MLF injury impairs adduction on the ipsilateral side. That is, a Left "One and a half" involves a Left horizontal gaze palsy (impairing abduction of the left eye and adduction of the right eye) and a Left INO (impairing adduction of the left eye), leaving only abduction of the right eye intact (with regard to horizontal eye movements).
What is the most common cause of "One and a Half" syndrome?
What do the terms intra-axial and fascicular mean with regard to ocular motor nerve palsies?
They both refer to the same thing. That is, ocular motor nerve palsy due to lesions of the nerve distal to the nucleus, but within the confines of the brainstem.
Over how many days does loss of function progress in a cranial mononeuropathy?
7 to 10 days
Within how many months does ocular misalignment due to ischemic ocular motor palsy usually improve?
What are risk factors for ischemic cranial mononeuropathy?
1) diabetes, 2) hypertensive vascular disease, 3) hypercholesterolemia
Which somatic muscles are innervated by the third nerve?
1) superior rectus, 2) inferior rectus, 3) medial rectus, 4) inferior oblique, 5) levator palpebrae superioris
What are the signs seen in a complete third nerve palsy?
1) complete ptosis, 2) eye positioned downward and outward, 3) dilated pupil that responds poorly to light
What is the most common cause of isolated unilateral third nerve palsy?
Presumed microvascular injury in the subarachnoid space or cavernous sinus
Aneurysms located where can give rise to a third nerve palsy involving the pupil?
At the junction of the posterior communicating artery in the internal carotid artery
Where do the pupillomotor fibers of the third nerve reside?
Superficially in the medial aspect of the third nerve
What is the most likely cause of a nontraumatic third nerve palsy with pupil involvement?
Aneurysm of the posterior communicating artery. Aneurysm should be assumed until proven otherwise.
What appearance will CSF have in the case of subarachnoid hemorrhage?
What type of imaging should be performed in the event of suspected third nerve palsy with pupillary involvement?
CTA or MRA (CTA is faster and has slightly greater resolution)
Is isolated efferent pupillary dysfunction usually benign?
Yes, it is not a form of third nerve palsy. Instead, it represents a tonic pupil, pharmacologically dilated pupil, or pupil that is mechanically damaged
What are the two forms of third nerve palsy for diagnostic purposes?
1) pupil-involving third nerve palsy and 2) pupil-sparing third nerve palsy (which further divides into pupil-sparing complete 3rd nerve palsy and pupil-sparing partial 3rd nerve palsy)
What is the most likely cause of a pupil-sparing third nerve palsy?
Ischemic cranial neuropathy
Is a pupil-sparing Complete third nerve palsy usually benign?
Yes, it is almost always benign and secondary to microvascular disease
Is a pupil-sparing Partial third nerve palsy usually benign?
Yes, but some are due to compressive lesions that may later progress to involve the pupil. MRI with contrast is indicated for a patient presenting with pupil-sparing Partial third nerve palsy.
Where does the third nerve branch into superior divisions?
At the superior orbital fissure or within the cavernous sinus
What does isolated involvement of either division of the third nerve usually indicate about the lesion?
That the lesion is anterior to the cavernous sinus or possibly the posterior orbit
What is the imaging study of choice for a divisional third nerve palsy?
MRI with contrast and fat suppression
What is a synkinetic phenomenon?
Co-contraction of muscles that normally are not activated at the same time. This often happens and aberrant regeneration of the third nerve
Does aberrant regeneration of the third nerve happen after microvascular ischemia?
No, but it may occur after trauma or compression by aneurysm or tumor
What is the Parks-Bielschowsky three-step test?
An algorithmic approach to identifying patterns of coular motility that cnoform to dysfunction of specific vertically acting extraocular muscles (usually a congenital 4th nerve palsy). It involves: 1) find the side of the hypertropia, 2) determine if the hypertropia is greater on left or right gaze, 3) determine if the hypertropia is greater on left or right head tilt
What is the most common complaint of a patient with a fourth nerve palsy?
Diplopia that is worse in down gaze (usually while reading)
What does bilateral fourth nerve palsy present with?
1) crossed hypertropia, 2) excyclotorsion of 10° or greater, 3) a large V pattern of strabismus, 4) habitual chin down posture
What are causes of congenital fourth nerve?
1) Anomalous superior oblique tendon, 2) anomalous site of superior oblique tendon insertion, 3) defect in the trochlea, 4) schwannoma of 4th nerve
What findings are seen in a unilateral fourth nerve palsy?
Ipsilateral hypertropia and contralateral head tilt
What is the most frequently affected nerve in isolated ocular motor palsy?
The sixth cranial nerve
How do patients with the sixth cranial nerve palsy present?
With horizontal diplopia that worsens on ipsilateral gaze, correlating with an abduction deficit and esodeviation that increases with gaze to the affected side
What is the most common cause of an isolated sixth nerve palsy?
What is Gradenigo syndrome?
Inflammation of the petrous bone leading to ipsilateral abducens palsy and facial pain
Do congenital sixth nerve palsies usually occur in isolation?
No they are usually part of a sydnrome such as Duane syndrome
Is neuroimaging required at the time of diagnosis of isolated sixth nerve palsy?
What is neuromyotonia?
Episodic abnormal activation of a nerve, usually in patients with a prior history of radiation therapy. During the episode of abnormal activation, overaction of the nerve produces ocular misalignment
Does benign microvascular disease often result in involvement of multiple cranial nerves?
No, usually only 1 ocular motor cranial nerve will be affected at a time in benign microvascular disease.
What is the hallmark ophthalmoplegia secondary to lesion the cavernous sinus?
Ipsilateral ocular motor nerve dysfunction involving a combination of third, fourth, fifth, and sixth cranial nerves and sympathetic fibers
What is Tolosa-Hunt syndrome?
And idiopathic sterile inflammation primarily affects the cavernous sinus. It is often accompanied by a "boring" pain
What sign is classic for carotid cavernous fistula?
Arterialization of conjunctival vessels
What are the two types of carotid cavernous sinus fistulas?
High-flow (usually occurring after severe head trauma) and low-flow (usually occurring spontaneously in older women)
What signs can indicate carotid cavernous sinus fistula?
Recombination increased intraocular pressure, proptosis, ocular motor neuropathy with diplopia, arterial or venous compromise to the retina and eye, ischemic optic neuropathy, choroidal effusions, pain, and cerebral venous infarction
What are myopathic, restrictive, and orbital causes of diplopia?
Thyroid disease, post traumatic destruction, post cataract extraction restriction, orbital myositis, orbital neoplasm, Brown syndrome
Which extraocular muscles are most commonly involved in thyroid eye disease?
The interior rectus and medial rectus
What is Brown syndrome?
A restrictive ocular motor disorder that produces limitation of upgaze when the affected eye is in the adducted position. It is often caused by a short superior oblique tendon when congenital.
What is nystagmus?
A rhythmic to-and-fro eye movement that incorporates slow phase
What is jerk nystagmus?
A form of nystagmus that has two phases: 1) a slow phase drift from the visual target, 2) a corrective saccade (fast phase) back to the target
What is pendular nystagmus?
A form of nystagmus involving back and forth slow phase movements that occurs without a fast phase
What is oscillopsia?
A sensation of environmental movement
How is jerk nystagmus named?
Jerk nystagmus is named for the direction of its fast phase component. The direction of the slow phase component, however, indicates where the pathology is.
What is dissociated nystagmus?
Nystagmus in which the amplitude of oscillations differs in each eye
What is disconjugate nystagmus?
Nystagmus in which the direction of oscillation differs between the two eyes
What is the usual pattern of infantile nystagmus syndrome?
Conjugate and horizontal
What is a null point of nystagmus?
The field of gaze in which nystagmus is minimal
What is latent nystagmus?
Early-onset, horizontal jerk nystagmus accentuated by or appearing only with monocular viewing conditions.
In which direction does the fast phase of latent nystagmus beat?
Toward the viewing (uncovered) eye. Latent nystagmus reverses direction when the opposite eye is covered. The slow phase is always toward the nose.
With what form of strabismus is latent nystagmus usually associated?
What is usually indicated by monocular vertical nystagmus in an infant?
Optic nerve or chiasmal tumor (glioma). It is usually accompanied by an APD and optic atrophy. Neuroimaging is warranted
What is spasmus nutans?
a disorder involving intermittent, binocular, small amplitude, high-frequency, horizontal, pendular nystagmus
How is spasmus nutans differentiated from infantile nystagmus syndrome (INS)?
Spasmus nutans involves abnormal head movements and head posture, and is often accompanied by torticollis.
What is the theoretical reason for the development of gaze-evoked nystagmus?
An inability to maintain fixation in eccentric gaze.
What is the direction of the fast phase of gaze-evoked nystagmus (GEN)?
In the direction of gaze.
What is Alexander's law?
A law regarding nystagmus that states that nystagmus increases in amplitude and frequency as the eyes are moved in the direction of the fast phase
Which nuclei serve as neural integrators for horizontal gaze?
Nucleus prepositus hypoglossi and medial vestibular nuclei
Which nucleus serves as the neural integrator for vertical gaze?
interstitial nucleus of Cajal
What are the potential causes of asymmetric gaze-evoked nystagmus?
stroke, demyelination, or tumor
What is rebound nystagmus?
Jerk nystagmus in the opposite direction of prolonged eccentric gaze
What is a common cause of rebound nystagmus?
From what does peripheral vestibular nystagmus arise?
From end organ dysfunction, including that of the semicircular canals, otolithic structures, and vestibular nerve
Hey peripheral vestibular lesion leads to gaze toward which side?
The contralateral side (away from the side of the lesion).
Does visual fixation dampen nystagmus due to peripheral vestibular lesions?
Vestibular nystagmus due to what cause is generally symmetric rather than asymmetric?
Systemic administration of ototoxic agents
What is the most common location of a lesion leading to downbeat nystagmus?
Cervical – medullary Junction
What is the most common location of a lesion leading to upbeat nystagmus?
What is the most common location of a lesion leading to periodic alternating nystagmus?
What is the most common location of a lesion leading to ocular bobbing?
Pontine – destructive lesion
What is the most common location of a lesion leading to ocular flutter/opsoclonus?
What is the most common location of a lesion leading to convergence-retraction nystagmus?
Pre-tectum (dorsal midbrain)
What is the most common location of a lesion leading to see-saw nystagmus?
What is the most common location of a lesion leading to monocular nystagmus of childhood?
What is the most common form of central vestibular nystagmus?
What is periodic alternating nystagmus (PAN)?
A strictly horizontal nystagmus that oscillates predictably in direction, amplitude, and frequency.
What are ductions?
individual movements of the eyes
What are versions?
Movements of the eyes together
What does the adjective comitant mean?
The same in all directions of gaze