Saturday, July 15, 2006

Neuroopthalmic Emergencies--Monocular visual loss

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Acute visual loss. Historically verify acuity, and whether the loss is retina, optic nerve or brain.
Historical points
acute angle glaucoma--Halos around lights suggests aberration of ocular media; with eye pain consider
Retinal disease-- may have micropsia (distortion of size) or metamorphopsia (of shape) which is not seen in optic nerve disorders. A discrete, sharply demarcated scotoma is characteristic of retinal disease.
Perception light flashes or photopsias, if prolonged, suggest retinal disease but if fleeting may be optic nerve disorder.
Optic nerve disorder--typically a relative afferent pupillary defect (RAPD) is present, although a small RAPD might be seen in retinal disorders occassionally. However, the retinal exam is abnormal here.

Optic perineuritis OPN contrast to ON. Patients may be older than in ON (36 % > 50), vision changes may be paracentral or arcuate, progress over weeks, have progressive vision loss, and respond dramatically to steroids, which are continued for months typically. MRI of orbits shows enhanced area is along optic nerve sheath, which is best seen on coronal images. Oral prednisone is not contraindicated.

Optic Neuritis-- ON is primarily a clinical diagnosis. It affects central vision and color vision, and progresses over days, with spontaneous recovery without treatment. Ipsilateral pain with eye movement is present. RAPD is always present. The optic disc acutely may show inflammation (papillitis) or normal (retrobulbar neuritis). MRI with contrast, especially including coronal images with fat suppression are very helpful (see images at linked site). ON shows enhancement of anterior half of optic nerve and coronal shows enhancement within the nerve substance (compare to optic perineuritis). Over 97 percent of cases enhance with MRI contrast. 95 % of patients have a good prognosis for recovery to 20/40 or better. Refer elsewhere for discussions of relation to MS and value of brain MRI or steroid treatment. Note that steroids can affect MRI enhancement. Caveats- vision loss for greater than 2 weeks, fever, other neurologic deficits require care. Rare causes-- (besides idiopathic or MS) include syphilis, sarcoid, and lyme disease. Autoimmune/ Sjogren's also can occur . CAVEAT beware of an opthalmic artery aneurysm.

Anterior ischemic optic neuropathy (AION)- more common than posterior ischemic optic neuropathy (PION). Presentation is monocular visual loss present on awakening, usually without pain. Vision loss is usually maximal at onset but one third may have progressive AION over first ten days post onset. You may see segemental disc edema and splinter hemorrhages, and small or no optic cup. In AION, divide into arteritic and nonarteritic (NAION) causes. NAION is often related to hypotension, change in hypertensive medications, vasospasm or sleep apnea syndrome (SAS). Ask about sildafenil (Viagra), decongestants. Carotid disease and emboli are uncommon, because due to laminar flow, emboli are more likely to arrive at central or branch retinal arteries. The rarer cases of carotid stenosis/occlusion may be heralded by dim vision with changes of posture or exertion, ipsilateral pain, and ipsilateral Horner's syndrome. Symptoms improve with resolution of optic edema. Contralateral symptoms may occur in 15-40 % of patients at some later point. In NAION, steroids, hyperbaric oxygen, optic neve sheath fenestration, and transvitreal radial optic neurotomy are not established. Empiric topical treatment with brimonidine tartrate (neuroprotective) or pentoxifylline have been used. ASA is used.

Arteritic AION (giant cell arteritis, temporal arteritis)- The average age at onset is 70, its rare under 60 and remote in patients under 50. Constitutional symptoms may be present for 2-3 months including loss of appetite, fever, night sweats, malaise and body aches. It may be preceded by episodes of transient monocular visual loss mimicking embolic events. Such episodic vision loss is an ominous sign of impending vision loss. The degree of vision loss may be profound including the loss of light perception. Fundoscopic exam shows a white swollen disc "pallid edema" (in contrast to hyperemic disc of NAION),a generous optic cup (contrast to nonarteric) and cotton wool spots, ipsilateral or contralateral, and central retinal or cilioretinal arterial occlusion is the sine qua non of GCA. The second eye becomes affected within about two weeks of the first. Labs such as ESR are normal in 20 %. C reactive protein is more sensitive and is not affected by anemia or plasma protein concentration (unlike ESR). Anemia, thrombocytosis (44 %) are common. Evaluation should include CBC, ESR, CRP. Investigational studies underway for IL-6. Biopsy is normal in 15-20 percent, but contralateral biopsy then has lower yield. GCA is a T cell mediated attack on the internal elastic lamina of medium and large arteries, causing ischemia. Treatment recommendations include (unproved) dexamethasone 10 mg iv push or Solumedrol one gram iv push. If vision loss is not acutely pending, oral regimen (60-100 mg/day). One regimen is 100 mg for a month, 80 mg for a month, 60 mg for a month, 40 mg for a month, then a slower taper with monitoring of lab. Vision loss is usually severe and permanent when it occurs, and it usually occurs in the first five days after initiation of treatment, and rarely with too rapid tapering. CAVEAT AION in a patient over 80 is likely to be arteritic. Ask about scalp tenderness, not just "headache." Ask about PMR,neck pain, jaw and tongue claudication (differentiate from TMJ), poor appetite and fever. A GENEROUS CUP TO DISC RATIO IS SO UNUSUAL IN NONARTERITIC AION THAT THIS FINDING ALONE SHOULD PROMPT A TA BIOPSY.

Retrobulbar optic neuropathy-- PION is usually due to GCA or hypotension, usually coupled with anemia. It may occur after lengthy surgery (back surgery), cardiac arrest or profound blood loss. CAVEAT rarely a compressive lesion at orbital apex, hyperacute retinal artery occlusion (first few hours) and acute disorders of intracranial optic nerves (aneurysms, pituitary adenomas and tumors) can mimic PION. Compressive retrobulbar neuropathy usually presents with painless vision loss, prominent dyschromatopsia, and comprises 6.5 % of patients evaluated for glaucoma (Ahmed et al. 2002). Commonest are pituitary lesions, meningiomas and aneurysms, can include pituitary apoplexy, craniopharyngiomas, chordomas, inflammatory lesions of paranasal sinuses, primary bone lesions (Paget's, osteopetrosis, fibrous dysplasia), orbital trauma (fracture, hemorrhage) , thyroid related eye diseases.

Opthalmic artery aneurysm-- usually presents with a slowly progressive optic neuropathy, but occassionally sudden expansion with hemorrhages, abrupt loss of vision, and pain mimicking ON. These are more common in women and often bilateral. The field defect may respect the vertical meridian which suggests intracranial origin which is unusual in ON. Nasal visual loss may mimic low tension glaucoma. Symptoms of SAH or older age at onset should point away from ON.

Pituitary apoplexy-- defined as hemorrhage into or infarction of a pituitary tumor. Clinical triad is headache, mental status changes and opthalmoplegia is classical. Presentation is abrupt severe headache, signs of meningeal irritation, change in mental status and vision changes. It may mimic aneurysmal SAH. Presentation may be bilateral and include oculomotor paresis (also unilateral or bilateral)involving the third, fourth and sixth cranial nerves, in that order of frequency. In most cases the tumor is not suspected. Precipitating factors can sometimes be identified and include increased blood flow to pituitary (Vasalva or hypotension), stimulation of the pituitary (pregnancy or exogenous estrogen), emboli from carotid surgery, coagulopathy, presence of thrombolytics or thrombocytopenia. Diagnosis is often missed on CT but should be apparent on MRI. Treatment includes stress dose steroids, electrolyte monitoring, and +/- surgical decompression.

Retinal artery occlusion (central retinal artery occlusion CRAO and branch retinal artery occlusion BRAO). Presentation is acute sudden, painless unilateral visual loss, possibly heralded by a flash of light. Unlike patients with AION who awaken with their deficit, patients with RAO recount what they were doing when the vision loss occurred. Many have curtain like vision loss or episodes of vision loss previously. While carotid disease is the commonest identifiable cause, only 11-45 % have carotid atherosclerosis after evaluation. Findings on examination are retinal whitening, cotton wool spots, box car segmentation of the blood column, cholesterol emoboli (yellow, from carotid artery or aortic arch) or calcific emboli (white, from heart or aorta) or platelet fibrin emboli (long and whitish, from heart or arteries). Prognosis is poor; although recanalization occurs, only 15 % recover vision. Treatment may include conservative modalities (ocular massage, paracentesis, and drugs) and invasive (thrombolytics) (see Kattah et al. Arch Opthal, 2002), The latter helped 10/12 patients but incompletely. Other modalities include pentoxifylline, and hyperbaric oxygen.

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