vision loss and VF Flashcards
Functional vision loss
There is a wide spectrum of functional vision loss presentations and a correspondingly large arsenal of tests to prove functional vision. A functional patient who claims NLP vision is generally easy to recognize. A normal response to the OKN drum or mirror test prove an approximate visual acuity of count fingers to 20/200.
Inability of a patient with NLP vision to perform propioreceptive tasks such as bringing two particular fingers together or writing their name on a sheet of paper proves a functional component to the vision loss but does not prove a specific level of vision. These tasks do not require visual acuity but rather rely on propioreception. You can test this yourself by closing your eyes and then bringing your two index fingers together (or by writing your name with eyes closed). Obviously if a patient has other neurological problems such as cerebellar ataxia or upper extremity weakness then those deficits may interfere with such testing but these findings should be evident on your exam of the patient. Most functional patients don’t know the nuances of the neurologic exam and erroneously assume that bringing two fingers together is a visual task.
In a patient with NLP vision in both eyes, normal pupillary light reflexes indicate that there is no causative pathology of the anterior portion of the visual pathways. Bilateral retrogeniculate pathology (AKA, posterior to the lateral geniculate nucleus) such as bilateral occipital lobe strokes, however, can cause bilateral NLP vision with normal pupillary light reflexes. Thus you can not rely on normally reactive pupils to prove functional vision loss in a patient with NLP vision in both eyes
Migraine associated vision loss
Migraine headaches can be preceded by visual auras during which patients classically experience a scotoma with jagged shimmering edges that expand and migrate across the visual field in one or both eyes. While this is the classic description of a visual aura, there is a great deal of variability among the appearance of visual auras. Generally however, almost all visual auras last 10-60 minutes. This becomes important diagnostically when investigating temporary vision loss. Amaurosis fugax, for instance, generally lasts 1-10 minutes while transient visual obscurations associated with papilledema or optic nerve head drusen last for a matter of seconds only.
ophthalmoplegic migraine
most commonly presents in children
Ophthalmoplegic migraine is characterized by episodic, localized orbital pain or headache associated with partial or complete paralysis of the oculomotor nerve. It is a very rare cause of episodic 3rd nerve palsy and virtually always presents in childhood (although subsequent attacks can carry over into adulthood).
The underlying etiology is unknown. Enhancement of the 3rd nerve on MRI and the intermittent nature of the attacks have led some to speculate that it is due to an undiagnosed focal inflammatory lesion such as a sarcoidosis or lymphoma. Some have speculated that these regions of enhancement represent schwannomas although skeptics point out that schwannomas usually cause progressive nerve weakness rather than the waxing and waning nature typical of ophthalmoplegic migraine. In general, ophthalmoplegic migraine remains a diagnosis of exclusion after other more sinister pathology such as lymphoma, leukemia, and infectious disorders have been ruled out by a spinal tap and/or systemic work-up.
Acute toxic optic neuropathies
Acute toxic optic neuropathies from methanol or ethylene glycol may present more commonly with global depression.
VF defects - nutritional
Cecocentral and/or central defects are classically seen in early toxic optic neuropathy and nutritional optic neuropathy. Global depression can occur in severe end-stage toxic optic neuropathy, but is not the most likely defect early in the disease course of slowly progressive toxic optic neuropathies.
Arcuate defects
Arcuate defects are typically seen in nerve fiber bundle defects caused by glaucoma and optic nerve drusen.
Ring scotoma VF
Ring scotomas are classic for retinitis pigmentosa, but could occur in acquired rod predominant degenerations such as vitamin A deficiency or melanoma associated retinopathy.
VF defect respecting vertical midline
Visual field defects respecting the vertical meridian and imitating a bitemporal hemianopia are not unusual in toxic neuropathy due to ethambutol.
Congenital cn4 palsy
A right 4th nerve palsy causes a right hypertropia worse in down gaze, left gaze, and right head tilt (all of which accentuate the weakness of the superior oblique muscle). As a result, patients with 4th nerve palsy will typically adopt a head tilt toward the contralateral shoulder and a gaze preference toward the side with the palsy (to allow more elevation from the superior rectus).
Normal vertical fusional amplitudes are about 2-3 diopters, but because patients with congenital 4th nerve palsy have had misalignment from birth, they are often able to fuse vertical deviations much larger than 3 diopters. Vertical fusional amplitudes are a very helpful test in distinguishing a longstanding congenital 4th nerve palsy that has just recently decompensated from an acute acquired 4th nerve palsy.
Because the tertiary action of the superior oblique is to abduct the eye (especially in down gaze), 4th nerve palsies can result in esotropia on down gaze which improves on up gaze. This V pattern can be seen in unilateral CN 4 palsy but is more common and more pronounced in bilateral CN 4 palsy.
Vetebrobasilar insufficiency
This patient has a classic presentation of vertebrobasilar insufficiency. Vertebrobasilar insufficiency can arise from hypoperfusion of the vertebral, basilar, or posterior cerebral arteries. Symptoms result from brainstem, cerebellar, and/or occipital lobe dysfunction and include transient dimming/blacking out of both eyes, ataxia, vertigo, dysarthria, dysphagia, and hemiparesis / hemiplegia.
An ESR and CRP could be ordered to evaluate for giant cell arteritis but this patient has no typical giant cell arteritis (GCA) symptoms and his visual blurring is highly atypical for GCA. GCA does not usually present with simultaneous bilateral transient vision loss and would likely have progressed to permanent vision loss after 6 months of symptoms. Usually, premonitory vision loss in GCA occurs within weeks of permanent vision loss.
While this patient’s account of vision loss could mimic migraine, it is highly atypical to develop new migraine auras at age 70. Also atypical, this patient has associated ataxia which is not expected from migraine.
Isolated occipital lobe seizures detected by an EEG could cause bilateral transient vision loss but usually have positive visual phenomena (simple hallucinations, photopsias, etc) and would be highly unusual in this setting.
Risk of stroke
All of the answer choices reflect carotid artery disease and increase the annual risk for stroke. Listed in order of increasing annual risk for stroke: asymptomatic carotid bruit (.1-.4% annual risk) < amaurosis fugax (2.0% annual risk) < symptomatic or asymptomatic retinal emboli (3.0% annual risk) < hemispheric TIA (8% annual risk). This data supports the culture of clinical practice. Carotid bruits are poorly correlated to significant carotid artery disease so most neuro-ophthalmologists have stopped listening for them. If the clinical scenario requires carotid evaluation, then some form of carotid imaging is performed (ultrasound, CTA, MRA, etc). Retinal emboli (even when asymptomatic) are powerful risk factors for subsequent stroke and must be worked up quickly in concert with the patient?s primary care provider. While both amaurosis fugax and hemispheric TIA usually share an underlying embolic etiology, hemispheric TIA carries the highest risk for subsequent CVA. By finding significant carotid disease in patients with amaurosis, retinal emboli, or hemispheric TIA, patients may be considered for carotid endarterectomy to reduce the rate of future stroke.
Posterior cortical atrophy (PCA)
Posterior cortical atrophy (PCA) is a slowly progressive senile degeneration that predominately affects the parietal and occipital lobes early in the disease course resulting in difficulty with visuospatial tasks and visual processing. Histopathology of PCA brain specimens usually shows an Alzheimer’s type of degeneration leading to the term “visual variant of Alzheimer’s disease” that is sometimes used as a synonym of PCA.
Patients with PCA often present with vague visual complaints & is frequently misdiagnosed because the complaints are vague, the ocular examination is structurally normal, and Snellen visual acuity may remain normal in the early stages of the disease. Over time the degeneration usually generalizes and results in memory deficits and cognitive decline similar to standard Alzheimer’s disease. Neuro-imaging studies such as CT and MRI may show a relative atrophy in the parieto-occipital region, may show only diffuse atrophy, or may be normal.
PCA can demonstrate a variety of visual deficits although the most common presentation is Balint syndrome (BS). BS is due to bilateral parieto-occipital dysfunction. The classic BS triad includes optic ataxia, acquired ocular motor apraxia, and simultanagnosia although most cases of Balint syndrome do not clearly demonstrate all three findings. Pts have difficulty with visuospatial tasks and visual processing.
-impairment of voluntary ocular movements so cannot recognize complex images but can recognize simple large images of letters
Ocular ischemic syndrome (OIS)
Ocular ischemic syndrome (OIS) has many manifestations in the eye including dot blot hemorrhages, macular edema, neovascularization of the retina/nerve/iris/angle, corneal edema, and prominent anterior chamber flare (with less marked cellular reaction). Because of diminished blood flow to the ciliary body, OIS usually results in low IOP.
Reasons for high IOP in OIS include hemorrhage in the AC or vitreous, angle closure from neovascularization of the angle, and a reperfusion IOP spike following carotid endarterectomy. Ciliary body hypoperfusion, not trabecular meshwork hypoperfusion, is the predominate effect of ocular ischemic syndrome.
Normal VF
60 degrees superior and nasal
75 degrees inferior field
110 degrees temporally
Surgical indications for IIH surgery
The indications for surgical intervention in IIH include progressive visual loss and/or intractable headaches despite maximal medical therapy.
Optic nerve sheath fenestration is the preferred procedure in cases with progressive visual loss. The fenestrations scar quickly, unfortunately, leading to a 15% success rate at 6 years.
When intractable headache is the predominate symptom, lumboperitoneal or ventriculoperitoneal shunts are the procedures of choice. These shunts are successful in relieving headache but have a high complication rate. Subsequent shunt revisions are required in approximately 50%. Serial “therapeutic” large volume lumbar taps were utilized in the past for treatment of IIH but this is no longer an accepted treatment of IIH. Long-term prednisone is unlikely to be effective for chronic IIH-related headache and has numerous serious side-effects.
Rod and cone lesions - VF assoc
least specific
RP = RING scotoma (loss of peripheral rods)
macular dz = central scotoma
Horizontal raphe
separates temporal superior retinal receptors from temporal inferior retinal receptors
NFL lesions that interrupt NFL of inner retina or ON up to jxn with the chiasm
Papillomacular bundle = central scotoma or cecocentral scotoma
Arcuate fibers
nasal radial fibers
papillomacular bundle (NFL)
Central scotoma - always inv/point of central fixation w/loss of VA
Paracentral scotoma - affects area of VF NASAL or temporal to the point of fixation
Cecocentral scotoma - point of central fixation and area b/t blind spot and fixation spot
Central/cecocentral scotoma causes
ON - compressive/toxic. Optic neuritis, AION, hereditary, nutritional
Retina - CSR, AMD, macular hole, cone dystrophy
Enlarged blind spot
optic nerve - papilledema, tilted nerve
retina - MEWDs, peripapillary atrophy
Homonyous VF defect - retrochiasm
congruous - posterior (toward occiput)
incongrous - anterior (towards chiasm)
