■ Techniques for visualizing these structures have progressed over the last century and a half, from illustrations based on ophthalmoscopy to newer technologies whose resolution can provide a nearly cellular level of detail.

■ Stereo photography is a widely used, albeit subjective, means of assessing optic nerve head topography.

■ Optic nerve head analyzers were the first instruments to use computers to assess the optic nerve head, by analyzing either stereoscopic photographs or the deflection of parallel lines of light. ■ Scanning laser ophthalmoscopy uses a diode laser to provide a three-dimensional image of the fundus. The confocal system helps remove stray light, increasing image quality.

■ The Heidelberg Retinal Tomograph II is a scanning laser ophthalmoscope that scans along multiple planes of depth, creating a three-dimensional image. This scan can provide quantitative topographic detail of the optic nerve head, which calculates optic nerve head parameters that may be useful in the clinical assessment of glaucoma.

■ The Scanning Laser Polarimeter (GDx) analyzes the “retardation” of polarized light to calculate the RNFL thickness, which makes it a useful test to assess nerve fiber layer defects in glaucoma.

■ Optical coherence tomography (OCT) uses low-coherence reflectometry to produce high-resolution, two-dimensional, cross-sectional images of the optic disc, retinal nerve fiber layer and macula. RNFL thickness measured with OCT has been shown to have good correlation with visual field defects in glaucoma. OCT has been used to study RNFL thickness in many other conditions, but its clinical utility in these settings is not yet established.

■ Enhancement of the optic nerve on MRI helps to identify inflammatory optic neuropathies. Ultra high resolution MRI may one day be available for extremely high resolution optic nerve images.

■ New imaging technologies can provide objective measurements that aid in the detection and evaluation of neuroophthalmic disease, especially optic nerve cupping associated with glaucoma, but they should only be used in conjunction with the clinical exam.

■ Ocular imaging technologies can be useful for the neuro-ophthalmologist, especially in identifying retinal pathology in cases of otherwise unexplained visual loss. Neuroimaging (i.e., MRI) of the optic nerve however, is an integral part of the evaluation of most patients with neurogenic visual loss.