Sudden Visual Loss

Patients with giant cell or temporal arteritis are at high risk of developing irreversible visual loss in one or both eyes. Therefore, maintaining a high index of suspicion is essential for early diagnosis and prevention of visual loss. Most patients with temporal arteritis are over the age of 60 years. When present, jaw claudication and neck pain are strongly suggestive of GCA. Other symptoms of GCA include headache, scalp tenderness, myalgia (polymyalgia rheumatica), and constitutional symptoms such as fever, malaise, weight loss, or anorexia. The temporal arteries may be prominent, tender, or pulseless but can also appear normal on clinical examination.

One or both eyes may experience vision loss, which can be transient or permanent. The most common cause of vision loss in giant cell arteritis is arteritic anterior ischemic optic neuropathy (A-AION). Table 1 lists the important features of the 2 types of AION—arteritic and nonarteritic. A relative afferent pupillary defect will be present unless there is bilateral symmetric involvement. The optic disc edema is typically pallid (Figure 1a and 1b); an exception to this is posterior ischemic optic neuropathy (PION), where the optic nerve appears normal since the infarction is retrobulbar. The visual loss tends to be more profound compared to nonarteritic AION. If vision loss is binocular, the second eye is usually involved within days of the first eye. Temporal arteritis should be considered in all patients over the age of 60 years who have AION, central retinal artery occlusion (CRAO), or cilioretinal artery occlusion. Other ocular manifestations include nerve fiber layer infarcts, choroidal infarcts, ocular ischemic syndrome, or diplopia (due to ischemia involving the extraocular muscles or cranial nerves).

Blood tests are not entirely sensitive or specific for GCA, although an elevated C-reactive protein (CRP), elevated erythrocyte sedimentation rate (ESR), and thrombocytosis are commonly present. An elevated CRP has a greater predictive value for GCA compared to an elevated ESR or thrombocytosis. The ESR can be normal in up to 20% of patients with GCA.

If GCA is suspected, high-dose systemic corticosteroids should be started immediately (oral prednisone, 1 to 2 mg/kg/day). Treatment with corticosteroids is not meant to restore vision; rather, it is used to halt the arteritic process and thereby preserve any remaining vision in either eye.

A temporal artery biopsy should be performed as soon as possible for a definitive diagnosis, preferably within 1 to 2 weeks of commencing corticosteroids. If the temporal artery biopsy specimen is negative and clinical suspicion for GCA remains high, a contralateral biopsy is recommended. Although other noninvasive tests have been suggested for diagnosing GCA, a temporal artery biopsy remains the most reliable confirmatory test.

Pituitary apoplexy is the result of infarction and/or hemorrhage into a pituitary tumor. The resulting hemorrhagic expansion of the pituitary tumor can cause mass effect on adjacent neural structures. Pituitary apoplexy should be considered whenever there is sudden blindness and/or ophthalmoplegia associated with headache.

Patients with pituitary apoplexy often have a sudden and severe headache due to meningeal irritation and stretching. If there is compression of the visual pathway, typically the optic chiasm, these patients develop progressive visual loss—visual field and possibly even visual acuity. If the adjacent ocular motor nerves are affected, there will be ophthalmoplegia and/or ptosis and it can be bilateral. If the trigeminal nerve is affected, facial pain or sensory loss can occur. Expansion of the hematoma may cause altered level of consciousness by compression of the brainstem. Involvement of the hypothalamus can result in thermoregulatory and cardiorespiratory dysfunction. Destruction of the pituitary gland causes endocrinologic deficiencies. It should be noted that these patients can have abrupt and rapid neurologic deterioration, with neck stiffness, nausea and vomiting, depressed level of consciousness, and even death.

The clinical presentation and subsequent confirmation by neuroimaging leads to the diagnosis of pituitary apoplexy. Both computed tomography (CT) and magnetic resonance imaging (MRI) are capable of demonstrating the hemorrhage. However, MRI is the preferred modality owing to its ability to better define the anatomic characteristics of adjacent neural structures, especially with coronal scans (Figure 2).

The immediate treatment is life-support measures and high-dose systemic corticosteroids to avoid acute adrenal insufficiency. Electrolyte, glucose, and hormone levels are important in the assessment as well as emergent consultation with an endocrinologist. Neurosurgical intervention is preferred in most cases, although some patients with pituitary apoplexy may improve with medical treatment alone. Early surgical decompression of the neural structures, either transcranial or transsphenoidal, provides the best prognosis for visual recovery.

Patients with occipital infarcts are often misdiagnosed as having an intraocular or functional problem, especially if the visual fields have not been adequately tested. Also, patients with bilateral occipital infarcts might potentially be confused with pituitary apoplexy. However, with occipital infarction, the pupillary light reaction is normal, as is the fundus and ocular motility examination. In addition, these patients will not typically have headaches. Hyperacute infarcts (first 6 hours) may be difficult to detect on neuroimaging unless diffusion-weighted images (DWI) are requested. Early recognition of these infarctions will allow expeditious referral to a stroke specialist.

Mucormycosis (phycomycosis or zygomycosis) is an aggressive, opportunistic fungal infection that usually enters the body through the respiratory tract mucosa. The infection occurs almost exclusively in patients who are immunocompromised or have metabolic abnormalities (eg, AIDS, organ transplant, diabetes mellitus, chronic renal failure), or who are on a regimen of chemotherapy or chronic corticosteroids. Rarely, mucormycosis infection has been noted in immunocompetent individuals. The fungal organisms invade blood vessels, causing ischemia and tissue necrosis. The necrotic tissue may be subtle and can be seen in the nares, nasal septum, nasopharynx, or palate; it often resembles black eschar. The fungus gains access to the orbit usually from the ethmoid sinuses. Subsequent spread via the ophthalmic artery, cribriform plate, or superior orbital fissure leads to intracranial involvement.

Early presentation may include fever, headache, and sinus pain. There can be a dark hue to the overlying skin. Orbital involvement results in proptosis, pain with extraocular movement, external ophthalmoplegia, conjunctival injection, chemosis, corneal anesthesia and ulceration, mydriasis, or vision loss. Vision loss is caused by retinal infarction, ophthalmic artery occlusion, and optic nerve infiltration. Involvement of the brain can result in stroke, intracranial hemorrhage, abscess formation, seizures, and death.

Neuroimaging is helpful in establishing a diagnosis of mucormycosis, but results may be normal in the early stages of infection. Therefore, the diagnosis requires a high index of clinical suspicion, highlighted by a careful inspection of the oral and nasal mucosa in at-risk individuals. A biopsy of necrotic-appearing tissue usually shows pauciseptate hyphae with right-angled branching. Other histologic characteristics include thrombosis from inflammatory occlusion, hemorrhage, and ischemic necrosis.

Rhinocerebral mucormycosis has a high mortality rate and is usually fatal in patients with AIDS, even with early diagnosis and intervention. The treatment includes extensive surgical debridement (possibly including orbital exenteration), intravenous amphotericin B, and consideration of hyperbaric oxygen. Liposomal amphotericin B has a lower toxicity and can be used in higher doses. Owing to the vaso-occlusive nature of the disease, it is difficult to achieve adequate tissue levels of amphotericin in the affected areas. Therefore, amphotericin soaks and local irrigation may be used as well. Posaconazole, a new triazole, has recently been FDA-approved. The typical dose used in the treatment of mucormycosis is 400 mg twice daily. Lastly, granulocyte colony-stimulating factor has been used in some patients with mucormycosis. The underlying condition causing immunocompromise should be carefully monitored and rectified if possible—correct acidosis, hypoxia, hyperglycemia, and electrolyte abnormalities. A multidisciplinary approach should be employed with otolaryngology, infectious diseases, pharmacy, and, if necessary, neurosurgical consultation.

Transient monocular visual loss (TMVL) and amaurosis fugax are used interchangeably to describe painless, transient vision loss in one eye, attributed to ischemia or vascular insufficiency and lasting for several seconds to a few minutes. Patients describe their vision loss as a shade or curtain coming down over their eye. TMVL usually occurs in people older than 50 who have atherosclerotic risk factors such as diabetes, hypertension, and hyperlipidemia. Also, coronary artery or peripheral vascular disease is often present, especially carotid artery stenosis. Frequently, patients may have had similar previous episodes or other cerebral transient ischemic attacks (TIAs). Owing to the transient nature, vision returns as the retina, optic nerve, or choroid are reperfused.

A retinal artery embolus is a common cause of amaurosis fugax and is occasionally seen in the retinal arteries. If an embolus remains stationary and is occlusive, vision loss can be permanent due to infarction of the retina, optic nerve, or choroid (Figure 3). Patients with TMVL or retinal artery occlusion (CRAO and BRAO) should be investigated to determine the source of the embolus. The work-up is similar to that of stroke in the brain. Carotid Doppler ultrasound is useful in assessing the extracranial carotid artery for atherosclerosis, stenosis, and velocities, especially at the carotid bifurcation. Magnetic resonance angiography, computerized tomographic angiography, or transcranial Doppler can be used to assess the intracranial carotid arteries. Transesophageal echocardiography is the study of choice for evaluating patients for a cardiac source of embolus. An electrocardiogram is recommended to rule out a cardiac arrhythmia that may predispose an individual to embolic events.

Experimental primate studies suggest that the retinal tolerance time for ischemia is 90 minutes until irreversible electrophysiologic changes occur. Unfortunately, most patients with retinal artery occlusion are probably not medically triaged within this period, leaving most of the information regarding treatment as anecdotal. Nevertheless, various treatments have been considered for retinal artery occlusion, including lowering intraocular pressure by systemic or topical agents, or by anterior chamber paracentesis; ocular massage to dislodge an embolus to the retinal periphery; carbogen (95% oxygen, 5% carbon dioxide) inhalation or paper bag rebreathing to induce retinal artery dilation; hyperbaric oxygen; and thrombolysis. The latter is not widely available due to limited expertise.

The North American Symptomatic Carotid Endarterectomy Trial (NASCET) found that carotid endarterectomy (CEA) for ipsilateral carotid stenosis of 70% to 99% in patients with carotid distribution TIA or TMVL is beneficial in preventing ipsilateral stroke. If the stenosis is 50% to 69%, the risk reduction is marginal, especially in women. Thus, the decision to do CEA in the latter group should be weighed against the morbidity and mortality of CEA. If the stenosis is less than 50%, then medical treatment alone is recommended.

If a cardiac source is identified, then referral to a cardiologist or cardiac surgeon is recommended for definitive management (eg, mural thrombus, valvular heart disease, patent foramen ovale, or arrhythmia). In fact, the most common cause of death in patients with RAO is cardiac disease. Thus, addressing the modifiable risk factors is important—smoking, hypertension, diabetes mellitus, hyperlipidemia, lack of exercise, and obesity.

Methanol (methyl alcohol) can be accidentally or intentionally ingested because of its close resemblance in smell and taste to conventional ethanol (ethyl alcohol). Occasionally, methanol is added to windshield wiper fluid to keep the fluid from freezing and also acts a degreaser. Methanol poisoning can initially present with nausea and vomiting. Within 1 to 2 days, patients develop abdominal pain, headaches, confusion, drowsiness, blurred vision, respiratory distress, and central nervous system depression. If the diagnosis goes unrecognized, death from coma and respiratory depression can occur.

Following ingestion, methanol is metabolized to formic acid, causing a metabolic acidosis with a high anion gap, reduced bicarbonate levels, and elevated serum formate and methanol levels. The mechanism for the optic neuropathy associated with methanol intoxication is attributed to the toxicity of formic acid to the retinal photoreceptors and/or the optic nerve. The degree of visual impairment depends on the amount of methanol ingested but is generally profound—loss of visual acuity with central or centrocecal scotomas. Owing to bilateral disease, a relative afferent pupil defect is typically absent; however, the pupillary light reaction can be sluggish in each eye. The optic discs appear normal, hyperemic, or edematous.

The treatment for methanol toxicity traditionally consists of inhibiting the metabolism of methanol with ethanol, correction of the metabolic acidosis, and, if necessary, hemodialysis. Alternately, fomepizole, an inhibitor of alcohol dehydrogenase, prevents the metabolism of methanol into formic acid. The best hope for visual recovery is predicated by early recognition and treatment. However, if the diagnosis is overlooked, patients can develop permanent visual loss with optic atrophy. The long-term management is complete abstinence of the offending agent.