Not uncommonly, patients present with complaints of visual loss in which the neuro-ophthalmic history and examination fail to provide a ready diagnosis. In fact, the final common pathway for unexplained visual loss and suspected nonorganic disorders is typically the neuro-ophthalmologist. Such patients may have no evident structural abnormalities of the eye, and the patient's complaints and history may not suggest any of the afferent visual disorders discussed in the previous chapters. This chapter discusses a variety of disorders that should be considered in patients who have unexplained visual loss.
Patients with unexplained visual loss may have subtle, undiagnosed ocular disease as the cause of their visual complaint. The neuro-ophthalmologist must therefore maintain an open mind during the entire examination, devoting as much attention to the slitlamp and retinal examinations as is given to testing the visual fields. The neurologist may need the help of an ophthalmology colleague, especially in patients with unexplained afferent visual complaints. This chapter discusses anterior segment and retinal disorders that mimic neuro-ophthalmic disorders.
ANTERIOR SEGMENT DISORDERS
Tear film disorders, such as dry eye syndrome, commonly cause transient visual blurring that may range in duration from seconds to hours in one or both eyes (see Table 1–3). Dry eye syndrome is very common in women older than 40 years, but is also associated with collagen vascular disease (Sjögren syndrome and many others), medications, systemic disorders (such as sarcoidosis), and neurological conditions (eg, progressive supranuclear palsy [PSP], Parkinson disease, facial nerve palsies). Patients frequently describe blurring that begins 2 to 3 minutes into a task requiring concentration, such as reading or driving. Sometimes the blurred vision clears momentarily with a blink. The patient's visual acuity may vary widely between examinations. A foreign body sensation and conjunctival injection are often present, but may not be prominent. Tear film disorders resulting in inadequate tear coverage can actually cause excessive tearing, but this reflex tearing consists of watery tears that fail to adhere to the ocular surface. Meibomian gland dysfunction and blepharitis can cause destabilization of the tear film and further exacerbate dry eye syndrome (Box 6–1).
BOX 6–1. TEAR FILM
The importance of the tear film in maintaining clear vision is not always appreciated by physicians. In addition to providing nutrients to the cornea, the tear film provides a smooth surface over the corneal curvature to optimize the optics of the eye. Tear film dysfunction is a very frequent cause of blurred vision, eye pain, red eyes, and tearing.
The tear film is complex, consisting of three distinct layers: (1) an inner mucous ...