Continuum, Neuro-Ophthalmology, August 2009, Volume 15, Issue 4

Visual loss from an optic neuropathy with disc edema has a broad differential diagnosis, including both congenital and acquired conditions: elevated intracranial pressure, ischemia, inflammation, demyelination, infection, neoplasia, paraneoplasia, and toxicity. Each of these categories of optic neuropathy has distinctive historical and examination findings that allow the physician to narrow the range of diagnostic possibilities or arrive at a single diagnosis. These categories will be reviewed in detail in this chapter.(C) 2009 American Academy of Neurology

Bilateral visual loss can occur with disease processes affecting both optic nerves, the chiasm, or the postchiasmal visual pathways. Each of these anatomic regions produces a different pattern of visual loss. Careful evaluation of visual acuity, pupillary reaction, color vision, formal visual field testing, and funduscopic examination allows localization to each of these regions. Different disease processes affect each region and will be reviewed in this chapter.(C) 2009 American Academy of Neurology

Visual hallucinations are defined as visual perceptions without an external stimulus. They arise from a variety of different processes, including decreased vision, drug exposure, and a variety of cerebral disorders. The description of the visual hallucination, accompanying history, and examination findings can help to decipher the underlying cause. The different types of hallucinations along with the anatomic basis and etiologies will be reviewed in this chapter. Higher cortical visual dysfunction is also reviewed in this chapter. Classic cortical visual syndromes occur with stroke or other disorders that affect a significant degree of higher-order visual cortex. Patients may also suffer from visual cortical dysfunction without the presence of a classic neurobehavioral syndrome, and visual symptoms may be vague and difficult to understand. A basic clinical understanding of visual hallucinations and higher cortical visual dysfunction will help the practitioner diagnose, manage, and appropriately treat patients with these syndromes.(C) 2009 American Academy of Neurology

Diplopia is rarely the favorite chief symptom for neurologists. Nonetheless, the underlying causes of diplopia often fall into the neurologist's purview, and a systematic approach renders the diagnosis and management tenable. Like most of neurology, the history is critical, and the examination serves to confirm initial localization hypotheses. The neurologist needs to master specialized techniques to qualify and quantify ocular misalignment in order to appropriately diagnose and manage binocular diplopia.(C) 2009 American Academy of Neurology

When evaluating a patient with diplopia, it is critical to differentiate monocular diplopia (diplopia present in one eye) from binocular diplopia (diplopia resolves with closure of either eye). Binocular diplopia is typically related to ocular misalignment and often has a neurologic cause. Although the supranuclear ocular motor system is primarily associated with generation of bilateral eye movements, certain supranuclear processes can cause ocular misalignment and binocular diplopia. Skew deviation, the most common supranuclear cause of diplopia, presents with binocular vertical diplopia due to a hypertropia and full ductions in each eye. Oculomotor nuclear lesions have distinct clinical characteristics related to the unique anatomy of the third cranial nerve nuclei, which may present with combinations, including bilateral ptosis and contralateral or bilateral ocular elevation deficits. Trochlear nuclear lesions clinically appear identical to fascicular or trochlear axonal lesions, but abducens nuclear lesions produce ipsilesional gaze palsies rather than unilateral cranial nerve VI palsies.(C) 2009 American Academy of Neurology

In addition to supranuclear, nuclear/infranuclear, and internuclear causes of diplopia, it is important to keep in mind neuromuscular and mechanical (extraocular muscle) causes of diplopia. Myasthenia gravis (MG) is the prototypical neuromuscular junction cause of diplopia and can mimic any pupil-sparing painless cause of diplopia; the eyelids are often diagnostically helpful in MG. MG is important to recognize not only because of the diplopic-related morbidity, but also because of the disease's potential to generalize and its association with thymoma. Several diseases, including trauma, neoplasm, sinus, and osseous pathology, affect the extraocular muscles, producing mechanically related binocular diplopia. Thyroid eye disease (TED) is the most common nontraumatic orbitopathy of adults and in its most extreme form has the potential to cause compressive optic neuropathy with attendant visual loss. TED is thought to be an autoimmune disorder that may occur in hyperthyroid, hypothyroid, or even euthyroid situations and most commonly affects the inferior and medial recti (producing esodeviations and hyperdeviations). Proptosis and eyelid dysfunction, most notably eyelid lag and retraction, are diagnostically helpful. TED management begins with an assessment of thyroid status.(C) 2009 American Academy of Neurology

Examination of the pupil can provide critical information in the evaluation of visual function. Pupillary examination is objective, requires little cooperation, and can be done in the unconscious patient, eg, allowing detection of traumatic optic neuropathy in an unconscious patient after a motor vehicle accident. Unlike other testing of visual function (acuity, colors, visual field) no subjective feedback from the patient is required, making pupillary examination a powerful tool in evaluating functional patients. Knowledge of the anatomy (sympathetic and parasympathetic pathways, iris sphincter, and dilator muscles) physiology (pupillary reactions, hippus) and examination techniques (swinging flashlight test) will be reviewed.(C) 2009 American Academy of Neurology