INTRODUCTION
Visual symptoms can be the presenting feature of a wide range of important neurological diseases. It is important for primary care clinicians to be familiar with the approach to these clinical scenarios to be able to triage care and direct appropriate initial diagnostic assessment, treatment, and referral for further evaluation. This chapter encompasses a practical, up-to-date overview of important considerations in the management of acute monocular visual loss, papilledema, visual field deficits, anisocoria, limitations of eye movements, and nystagmus.
ACUTE MONOCULAR VISUAL LOSS
Acute visual loss of one eye is a common symptom that requires urgent evaluation and management, usually requiring ophthalmologic consultation. As a first step, it is critical to identify whether visual loss is due to a lesion in the eye (especially retinal disease) or the optic nerve. A retinal lesion may be suggested by reported symptoms of metamorphopsia (wavy, warped images), positive phenomena (flashing or colored lights), or a sudden increase in “floaters” in one eye. In contrast, optic nerve lesions tend to present with visual loss (often with significant color desaturation), without prominent metamorphopsia, positive phenomena, or floaters.
The tempo of visual loss is key to making an accurate diagnosis; for example, with optic neuritis visual loss evolves quickly and then subsequently improves; with ischemic optic neuropathy, it is sudden and fairly static; with compressive lesions, its discovery may be sudden, but its occurrence is more likely to be insidious and slowly progressive. The presence or absence of pain is also important to establishing the correct diagnosis; for example, pain is typically present in disorders such as optic neuritis or giant cell arteritis (GCA) but absent in nonarteritic ischemic optic neuropathy (NAION).
A dilated fundus examination typically must be performed to diagnose conditions such as retinal or vitreous detachment, arterial or venous occlusion, or other retinal pathology. Occlusion of the central retinal artery is characterized by diffuse retinal whitening with a macular cherry-red spot ( Fig. 4.1 ). This occurs because the inner layers of the retina, which are normally transparent, become swollen due to acute ischemia and obscure the normal color observed in the pigment epithelial layer in the outer retina. The cherry-red spot is seen in the macula because the normal retina is thinnest in this location, so there is less swelling of the inner layers. With branch retinal artery occlusion the areas of retinal ischemia are more circumscribed. Diabetic macular ischemia often produces macular edema in association with retinal microhemorrhages and cotton wool spots (cotton wool spots also represent areas of ischemia where the inner retinal layers are no longer transparent to light). A retinal vein occlusion produces profuse intraretinal hemorrhages ( Fig. 4.2 ).
The hallmark of unilateral optic neuropathy is the relative afferent pupillary defect (RAPD) ( Fig. 4.3 ). The RAPD is identified by the swinging flashlight test, during which light is alternately directed toward each pupil. When light is shined into the unaffected eye, both pupils constrict normally. When light is swung to the affected eye, both pupils should stay constricted. However, dilation of both pupils when the light is swung to the affected eye indicates an RAPD and strongly suggests an optic neuropathy on that side.
A slit-lamp examination provides detailed inspection of the anterior structures of the eye, allowing the diagnosis of conditions such as uveitis. In some circumstances, the ophthalmologic evaluation will include additional imaging and electrophysiologic studies such as optical coherence tomography (which provides high-resolution cross-sectional images of the retina), fluorescein angiography, or electroretinography.
Magnetic resonance imaging (MRI) of the orbit is often the most helpful diagnostic test in patients with a suspected optic nerve disorder and can help distinguish inflammatory, ischemic, and neoplastic causes. As opposed to standard MRI of the brain, MRI of the orbit includes coronal views with suppression of the orbital fat, thus permitting better visualization of the optic nerve.
Optic Neuritis
Optic neuritis most often occurs between the ages of 20 and 50 and is three times more frequent in females. Visual loss usually reaches its nadir within 7 to 10 days and begins to recover within 1 month. Retro-orbital pain, particularly with eye movements, occurs in almost all cases.
The likelihood of optic neuritis progressing to multiple sclerosis (MS) is best predicted by brain MRI at the time of diagnosis. Patients with other white matter lesions are at very high risk of a subsequent clinical relapse; consultation with a neurologist or MS specialist is needed to assess the benefit and risk of a growing number of available disease-modifying treatments.
Treatment with intravenous corticosteroids may hasten the recovery of visual deficits from optic neuritis, although it does not significantly affect long-term visual outcomes. Treatment with oral corticosteroids, on the other hand, may be associated with an increased risk of recurrence of optic neuritis, and this therapy should be avoided.
Neuromyelitis optica spectrum disorder (NMOSD) is a rare autoimmune condition that causes severe optic neuritis and myelitis, but many patients will not have both. Aggressive treatment in the form of plasma exchange may be warranted in suspected cases, because spontaneous recovery can be poor. The aquaporin 4-IgG (anti-AQP4) and anti–myelin oligodendrocyte glycoprotein serum tests are highly specific for NMOSD. The identification of these antibodies has implications for prognosis and optimal long-term immunosuppressive treatment, compared to patients with typical optic neuritis.
Ischemic Optic Neuropathy
Ischemic injury to the optic nerve can be either arteritic or nonarteritic. NAION most commonly affects adults over the age of 50 and causes acute, painless visual loss. Nocturnal hypotension (possibly precipitated by antihypertensive therapy) may provoke the ischemic event. The affected optic disk is swollen and often has surrounding hemorrhages in the acute phase. Recovery tends to be poor.
Ischemic optic neuropathy can also occur in the setting of GCA. The prevalence of GCA increases with age and is rare under the age of 60. Systemic symptoms may include myalgia, jaw claudication, fever, malaise, and scalp tenderness. The diagnosis is suggested by an elevated erythrocyte sedimentation rate and C-reactive protein and confirmed by evidence of inflammation on a temporal artery biopsy. Depending on the level of clinical suspicion, temporal artery ultrasound can provide useful information to determine whether additional diagnostic testing or empiric treatment should be pursued. Given the potentially high risk of progressive, irreversible visual loss, empiric treatment with corticosteroids should be initiated promptly in suspected cases, without delaying for a biopsy to be performed.
PAPILLEDEMA
Papilledema refers to optic disk swelling specifically caused by elevated intracranial pressure (ICP) ( Fig. 4.4 ). Papilledema may be one manifestation of a neurologic emergency, and its presence therefore requires immediate diagnostic evaluation. The more generic term “optic disk edema” is used to describe other causes of intrinsic optic nerve swelling (e.g., optic neuritis, NAION) in which the ICP is not elevated. True papilledema must also be differentiated from other optic nerve anomalies, such as optic disk drusen ( Fig. 4.5 ). One key feature that helps distinguish papilledema from so-called “pseudo-papilledema” is the obscuration of vasculature across the optic disk margins. The observation of spontaneous venous pulsations is not considered highly reliable for the distinction of various causes of optic disk edema.
Symptoms of elevated ICP that accompany papilledema include headache, pulsatile tinnitus, nausea, vomiting, and diplopia. Transient visual obscurations are common, consisting of fleeting, painless blackouts of vision that occur on changing posture.
It is important to recognize that visual acuity is often normal in the presence of papilledema, as opposed to other causes of optic disk edema, in which the acuity is commonly reduced. Acuity becomes compromised from papilledema when optic nerve damage is severe or peripapillary retinal swelling has extended to the macula itself.
Automated visual field assessment is essential to the evaluation and management of patients with papilledema. Enlargement of the blind spots and constriction of peripheral vision are typical. Progression of visual field abnormalities is a critical parameter that affects treatment decisions.
The differential diagnosis for elevated ICP includes an intracranial or intraspinal mass lesion, cerebral venous thrombosis, meningitis, subarachnoid hemorrhage, and intracranial hypertension secondary to medication or systemic medical conditions. Appropriate imaging studies include either a computed tomography (CT) or MRI study of the brain, with CT- or MR venography to evaluate the possibility of venous thrombosis. Lumbar puncture provides critical diagnostic information in a patient with papilledema and can generally be performed safely (unless there is a space-occupying lesion that poses increased risk of herniation). Basic cerebrospinal fluid (CSF) studies help identify infectious, inflammatory, and neoplastic conditions affecting CSF circulation and provide a measure of the ICP.
The diagnosis of idiopathic intracranial hypertension (IIH, pseudotumor cerebri) is established when neuroimaging and spinal fluid examination yield no other explanation for elevated ICP. IIH shows a female predominance and is highly associated with obesity or recent weight gain. Weight loss is a critical component of effective treatment for IIH. Medical therapy often includes acetazolamide, a carbonic anhydrase inhibitor that decreases CSF production. Topiramate may be considered as an alternative. When visual loss progresses despite medical treatments for papilledema, surgical treatments, including cerebrospinal shunting procedures, are considered. Patients with IIH often have narrowing of cerebral venous sinuses, visible on MRI or CT venography. In some cases of medically refractory IIH, catheter venography may demonstrate a venous stenosis that is hemodynamically significant and amenable to stenting, which can reduce the ICP.
PROGRESSIVE VISUAL LOSS FROM OPTIC NEUROPATHIES
Glaucomatous optic neuropathy is among the most common causes of progressive visual loss. Open angle glaucoma typically produces fairly symmetric progressive visual field loss with optic disk cupping and elevated intraocular pressure ( Fig. 4.6 ). A variety of mass lesions (including meningioma and pituitary adenoma) can also cause progressive vision loss from compression of the optic nerve. Therefore while imaging studies are not necessary for a typical case of glaucoma, they are necessary in any case that the presentation is atypical.
