NEURO-OPHTHALMOLOGY UPDATE
From the 6th Annual Downeast Ophthalmology Symposium, presented by the Maine Society of Eye Physicians and
Surgeons, Manchester, ME
Thomas R. Hedges III, MD, Professor of Ophthalmology and Neurology, Tufts University School of Medicine, and
Director of Neuro-ophthalmology, New England Eye Center, Tufts New England Medical Center, Boston, MA
| EVALUATING PATIENTS WITH PRESUMED OPTIC NEUROPATHY
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| Determining whether vision loss due to optic neuropathy (ON): 3 requirements 1) loss of central vision (visual
acuity may be preserved; visual field defect present); 2) change in color vision (helpful in distinguishing ON
from retinopathy; 3) relative afferent pupillary defect (probably most important objective finding)
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 | Visual acuity: speaker checks this himself; helpful to listen to how patient reads chart (missing letters on one side
clue to visual field defect)
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| Contrast sensitivity: sometimes helpful in patients with 20/20 acuity and ON (patient may see small letters in
high contrast but be unable to see larger letters in low contrast); affected by other conditions
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| Color vision: type of color vision plates not important; talk to patient about subjective sense of difference in color
as seen by each eye; speaker does not quantify color
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| Visual field testing: tangent screen may be useful; speaker uses laser pointer (pinching fingers over pointer makes
light dimmer and enables detection of small subtle defects, eg, those from occipital lesions); Amsler grid—makes
field defects apparent; almost all field defects affect central vision because most optic nerve fibers carrying information
from central portion of visual field; most of occipital cortex responsible for central part of visual field; if patient
says area not missing but distorted, consider occult macular problem
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| Checking pupils: light of direct ophthalmoscope enables visualization of pupil against black iris; observation of
red reflex with direct ophthalmoscope provides better way to see relative afferent pupillary defect; observation of
more robust normal response in fellow eye helpful; spending equal time on both eyes helps in detecting subtle afferent
defects
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| Nerve fiber bundle defects: reflect disease of optic disc; even tiny defect at level of optic nerve head leads to
larger area of temporal retina that does not send information to brain, so visual field defects larger in nasal field; automated
perimetry—does not give detail obtained with tangent screen, so anatomy may not be clearly reflected; pattern
recognition—facilitates detection of arcuate scotomata
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| Anomalies of optic disc: swelling of disc and arcuate field defect indication of anterior ischemic optic neuropathy
(AION); myelinated nerve fibers may be incorrectly interpreted as papilledema; tilted nerves frequently cause bilateral
temporal field defects, giving appearance of bitemporal hemianopia from chiasmal compressive lesion; hypoplastic
optic nerves tend to have anterior field defects, usually discovered incidentally; optic disc drusen, like
AION and glaucoma, cause arcuate field defects; important to distinguish drusen and pseudopapilledema from active
disc swelling by looking for hemorrhages in disc; occasional patient may have crowded nerve and incidental
hemorrhage; optical coherence tomography (OCT)—used to distinguish congenital disc swelling from patients with
mild papilledema; patients with mild papilledema and those with disc swelling without drusen show swelling of
nerve fiber layer on OCT; speaker obtains OCT, then has patient return; if no change, can extrapolate backward
and say nerve has always been crowded
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| Visual loss from papilledema: variety of mechanisms include choroidal folds, retinal hemorrhages, and progressive
development of optic atrophy; macular edema can occur under retina as well as within it (observed on OCT);
speaker studied series of patients with AION, papilledema, and subretinal fluid (rare; many improve as fluid recedes);
loss of nerve fiber layer—most often, progressive loss of superior fibers cause inferior nasal visual field defect
(typical for papilledema); hypertension—check blood pressure of patients who present with optic disc
swelling; patients with AION frequently hypertensive (in younger patients, hypertension highly labile)
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| Retrobulbar ON: consider in patients with less discrete more central scotomata; determine rate of progression of
visual loss (progressive, rapidly progressive, or acute); chronic progressive process suggests presence of compressive
lesion, eg, small meningioma invading optic canal; meningioma—once in canal, can have significant effect on
vision and can become more rapidly progressive; obtain magnetic resonance imaging (MRI) with fat suppression
and gadolinium enhancement; also look at coronal sections
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| Conditions that mimic ON: consider when 3 main components of ON not present; visual evoked potentials
(VEP)—speaker uses for patients with visual loss that seems fictitious or functional; helpful if normal; multifocal
VEP—use in patients with visual field defects not associated with afferent pupillary defect or loss of color vision;
under development; standard as well as multifocal VEP abnormal if macular disease present; electroretinography
(ERG)—used for diffuse retinal disorders and cone dystrophy (mimics ON)
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| Pituitary adenoma: patient had bitemporal hemianopia; hemiarcuate pattern to field defect (can have somewhat arcuate
pattern of nerve fiber layer defect, even with disease in optic nerve or chiasm); bitemporal loss reflected in
ERG, ie, decreased amplitude and increased latency
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| Retinal disorders: patient told she had ON, but had no afferent pupillary defect and no loss of color vision; visual
field testing showed no arcuate scotoma, just enlarged blind spot; multifocal ERG proved retinal process (decreased
signal corresponded to enlargement of blind spot); if volume of visual field significantly affected, afferent
pupillary defect seen in retinal disease
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| Hereditary, toxic, or nutritional ON: consider if central scotoma bilateral and somewhat symmetrical; Leber’s hereditary
ON—specific mutation found on blood tests; young children (eg, 8-10 yr of age) can recover (takes ≈1
yr); cannot predict recovery with OCT; first eye affected, then may be months before second eye affected; in
acute phase, look in peripapillary retina for telangiectatic vessels; patients may develop what looks like bitemporal
hemianopia and have falsely reduced visual acuity due to splitting of macula by paracentral hemianopic field
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| DIAGNOSIS AND MANAGEMENT OF THIRD NERVE PALSY
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| Isolated third nerve palsy (TNP): if aneurysm strongly suspected, computed tomographic angiography (CTA)
best test
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| Symptoms: pain can be severe in patients with small-vessel disease, eg, microvascular TNP from diabetes
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| Signs: should have combination of 2 or 3 muscles involved, eg, patient who has only ptosis or only mydriasis probably
does not have TNP; if patient has all components, ie, ptosis, plus dysfunction of medial rectus, inferior rectus,
inferior oblique, and superior rectus muscles (particularly if pupil involved), TNP present and must be dealt with
emergently
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| Conditions that mimic TNP: thyroid eye disease; myasthenia gravis; ophthalmoplegia; inflammatory conditions,
eg, Tolosa-Hunt syndrome (patients steroid-responsive and have combination of nerve palsies); silent sinus syndrome
(inflammation and pus in maxillary sinus may pull orbital floor downward and tether inferior rectus); orbital
tumor
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| Cavernous sinus lesions: if patient has ptosis, medial rectus dysfunction, and pupillary dysfunction, test for involvement
of other cranial nerves; if other nerves involved, consider cavernous sinus lesion; sympathetic and parasympathetic
fibers can be affected simultaneously, and if they balance out, pupil appears normal; intracavernous
aneurysms—grow slowly and tend not to rupture (rupture may cause fistula and shunting of blood into superior
ophthalmic vein); pituitary adenoma—of 3 oculomotor nerves, third most commonly affected; swollen pituitary
gland may compress third nerve just before it enters cavernous sinus; if tumor bleeds, it can expand rapidly, causing
acute TNP (form of pituitary apoplexy); meningioma—can compress third nerve
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| Work-up of TNP: check for any degree of pupillary involvement; if pupil completely spared in presence of significant
third nerve dysfunction, and if patient diabetic, microvascular TNP diagnosed; any degree of pupillary involvement
significant; however, up to one-third of patients with small-vessel disease have pupillary involvement,
so strongly consider aneurysm; partial TNP with partial pupillary involvement considered pupil-involved TNP and
taken seriously; isolated pupillary dilatation—if no ptosis present and Maddox rods show no evidence of third nerve
dysfunction, aneurysm ruled out; pupillary fibers in perfect position to be affected by aneurysm; at same time, pupillary
fibers peripheral, so that ischemia within core of nerve spares them; small-vessel disease and infiltrative
processes, eg, from lymphoma, may also spare pupil; serial sections show lesions either in cavernous sinus or intrapeduncular
cistern, with core of nerve being ischemic and pupillary fibers spared (most patients recover over ≈3
mo)
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| Intracranial TNP: intracavernous or in prepontine region; consider aneurysm (posterior communicating artery aneurysms
and basilar artery aneurysms can affect third nerve); midbrain lesions can affect pupil, but other associated
findings usually present; demyelinating lesions—eg, multiple sclerosis (MS); many patients with MS have
bilateral internuclear ophthalmoplegia; older patients with acute internuclear ophthalmoplegia have infarcts, not
TNP
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| Aneurysms: posterior communicating artery—travels with third nerve; aneurysm affects nerve at junction of carotid
and posterior communicating arteries; top of basilar artery—aneurysms here tend to be larger, more chronic and
progressive, and cause partial third nerve dysfunction; aberrant regeneration—seen with both types of aneurysms;
usually follows TNP by ≈90 days; CTA—shows artery and associated hemorrhage, if present; study of
choice for patients suspected of having aneurysms; can see aneurysm almost 100% of time if >4 mm (to affect
third nerve, aneurysm in posterior communicating artery must be >4 mm before rupture); CTA safer for older patients
than conventional angiography
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| Aberrant regeneration of third nerve: primary—in patient with TNP, indicates underlying compressive lesion
that may be aneurysm or tumor; never follows ischemic TNP; eyelid findings—ptosis; when patient looks down, lid
moves up (“does not necessarily fly up like a window shade”); when patient looks inward, eyelid may come up;
when patient looks upward, eye may turn in (inappropriate input from superior rectus to medial rectus); when patient
adducts eye, pupil may constrict (pseudo-Argyll Robertson pupil); secondary—due to head trauma, although
TNP after mild head trauma probably not directly due to trauma (indicates presence of basal skull tumor); head
trauma must be severe (patient must have lost consciousness and sustained skull fracture) to cause avulsion of third
nerve
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| Summary: when patient appears to have TNP, make sure appropriate muscles involved; if only 1 or 2 muscles involved,
consider other condition mimicking TNP and obtain orbital studies; if only ptosis or only mydriasis
present, condition probably not TNP; consider Adie’s pupil or other pupillary dysfunction; if TNP alone present,
consider aneurysm; if some pupillary involvement and partial TNP, consider aneurysm; rule aneurysm out or in
with CT and CTA; in young patient whose studies equivocal, consider MRI or conventional angiography; in older
patients, consider MRI because of complications of angiography; older patients, even with pupillary involvement,
often have microvascular TNP and can be observed
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Suggested Reading
Arnold AC: Evolving management of optic neuritis and multiple sclerosis. Am J Ophthalmol 139:1101, 2005; Chen
Z et al: Pituitary apoplexy presenting as unilateral third cranial nerve palsy after coronary artery bypass surgery.
Anesth Analg 98:46, 2004; Egan RA et al: A contribution to the natural history of optic nerve sheath meningiomas.
Arch Ophthalmol 120:1505, 2002; Hickman SJ et al: Management of acute optic neuritis. Lancet 360:1953, 2002;
Hoffmann EM et al: Inter-eye comparison of patterns of visual field loss in patients with glaucomatous optic neuropathy.
Am J Ophthalmol 141:703, 2006; Hoye VJ 3rd et al: Optical coherence tomography demonstrates subretinal
macular edema from papilledema. Arch Ophthalmol 119:1287, 2001; Kau HC et al: High-resolution magnetic
resonance imaging of the extraocular muscles and nerves demonstrates various etiologies of third nerve palsy. Am J
Ophthalmol 143:280, 2007; Epub 2006 Nov 27. Kupersmith MJ et al: Magnetic resonance angiography and clinical
evaluation of third nerve palsies and posterior communicating artery aneurysms. J Neurosurg 105:228, 2006;
Kwan ES et al: Tolosa-Hunt syndrome revisited: not necessarily a diagnosis of exclusion. AJR Am J Roentgenol
150:413, 1988; Lee AG et al: The rate of visual field loss in optic nerve head drusen. Am J Ophthalmol 139:1062,
2005; Massicotte EC et al: Multifocal visual evoked potential in nonorganic visual field loss. Arch Ophthalmol
123:364, 2005; Newman NJ: Hereditary optic neuropathies: from the mitochondria to the optic nerve. Am J Ophthalmol
140:517, 2005; Pirko I et al: The natural history of recurrent optic neuritis. Arch Neurol 61:1401, 2004;
Soares-Welch CV et al: Optic neuropathy of Graves disease: results of transantral orbital decompression and
long-term follow-up in 215 patients. Am J Ophthalmol 136:433, 2003.
Educational Objectives
| The goal of this program is to improve the evaluation of patients presumed to have optic neuropathy (ON)
and the diagnosis and management of third nerve palsy (TNP). After hearing and assimilating this program,
the clinician will be better able to:
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| 1. Perform testing for loss of central vision, changes in color vision, and afferent pupillary defects in
patients suspected of having ON.
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| 2. List anomalies of the optic disc that must be ruled out in the evaluation for possible ON
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| 3. Describe conditions that mimic ON.
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| 4. List conditions that mimic TNP.
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| 5. Perform a thorough work-up for TNP.
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Faculty Disclosure
In adherence to ACCME Standards for Commercial Support, Audio-Digest requires all faculty and planning committee
members to disclose relevant financial relationships within the past 12 months that might create any personal conflicts of
interest. Any identified conflicts were resolved to ensure that this educational activity promotes quality in health care
and not a proprietary business or commercial interest. For this program, the faculty and planning committee reported
nothing to disclose.
Acknowledgements
Dr. Hedges spoke at the 6th Annual Downeast Ophthalmology Symposium, held September 28-30, 2007, in Bar Harbor
ME, presented by the Maine Society of Eye Physicians and Surgeons. The Audio-Digest Foundation thanks Dr. Hedges
and the Maine Society of Eye Physicians and Surgeons for their cooperation in the production of this program.
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