Neuro-ophthalmology: Visual Fields

Visual field testing is an important part of the assessment of the afferent visual system. This chapter reviews the clinical process of visual field evaluation and the localization of lesions that affect the visual system. The visual field can be thought of as an island with an outer edge beyond which one cannot see and with an elevated center. The normal extent of the peripheral field of vision from the center is 90° to 100° temporally, 75° inferiorly, and 60° nasally and superiorly. Visual fields are subjective and should be considered only 1 part of the examination of the visual pathways.

Optical Coherence Tomography in Multiple Sclerosis

Optical coherence tomography (OCT) grew out of a convergence of rapid advancements in femtoseconds optics research and fiber optic commercial technology. The basic concept of OCT is to “see” into tissues using light echoes, analogous to the sound echoes of ultrasonography. Multiple A-scans are assembled into a B-scan two-dimensional image of the tissue of interest. Retina is an ideal tissue for evaluation by OCT, since the eye is designed to minimize light scattering through the anterior chamber and vitreous. OCT has had a significant impact on the field of multiple sclerosis, where it has allowed direct imaging of the myelin-free segments of axons and cell bodies of retinal ganglion cells. Together with precise functional measurements of the afferent visual system, the addition of robust structural measurements of retinal injury has allowed for an unprecedented ability to correlate clinical effects with the degree of neuronal loss. In addition, OCT has proven helpful to distinguish different forms of demyelinating disease, such as multiple sclerosis (MS) and neuromyelitis optica, and has provided ideal outcome measures in remyelination and neuroprotection trials.

Transient Vision Loss

Transient vision loss is common and often results from a transient loss of blood supply to the afferent visual system, although there are many other potential causes. In this chapter, we begin by listing the common causes of transient vision loss. We next discuss the approach to transient vision loss. We emphasize the importance of the history, since physical examination and workup may be unrevealing. We then review the diagnostic evaluation, with a focus on investigations for transient vision loss that is vascular in etiology. Lastly, we discuss the management approach for patients with a cardiac source of embolism or internal carotid artery stenosis.

Microstructural visual system changes in AQP4-antibody–seropositive NMOSD

Objective:To trace microstructural changes in patients with aquaporin-4 antibody (AQP4-ab)-seropositive neuromyelitis optica spectrum disorders (NMOSDs) by investigating the afferent visual system in patients without clinically overt visual symptoms or visual pathway lesions.Methods:Of 51 screened patients with NMOSD from a longitudinal observational cohort study, we compared 6 AQP4-ab–seropositive NMOSD patients with longitudinally extensive transverse myelitis (LETM) but no history of optic neuritis (ON) or other bout (NMOSD-LETM) to 19 AQP4-ab–seropositive NMOSD patients with previous ON (NMOSD-ON) and 26 healthy controls (HCs). Foveal thickness (FT), peripapillary retinal nerve fiber layer (pRNFL) thickness, and ganglion cell and inner plexiform layer (GCIPL) thickness were measured with optical coherence tomography (OCT). Microstructural changes in the optic radiation (OR) were investigated using diffusion tensor imaging (DTI). Visual function was determined by high-contrast visual acuity (VA). OCT results were confirmed in a second independent cohort.Results:FT was reduced in both patients with NMOSD-LETM (p = 3.52e−14) and NMOSD-ON (p = 1.24e−16) in comparison with HC. Probabilistic tractography showed fractional anisotropy reduction in the OR in patients with NMOSD-LETM (p = 0.046) and NMOSD-ON (p = 1.50e−5) compared with HC. Only patients with NMOSD-ON but not NMOSD-LETM showed neuroaxonal damage in the form of pRNFL and GCIPL thinning. VA was normal in patients with NMOSD-LETM and was not associated with OCT or DTI parameters.Conclusions:Patients with AQP4-ab–seropositive NMOSD without a history of ON have microstructural changes in the afferent visual system. The localization of retinal changes around the Müller-cell rich fovea supports a retinal astrocytopathy.

Transient Visual Loss

Transient visual loss is common and often due to a transient loss of blood supply to the afferent visual system, although there are many other potential causes. We review the approach to the patient with transient visual loss in this chapter, with special attention to vascular causes.