Retinal imaging has an illustrious history tracing back to 1850, when Hermann von Helmholtz invented the ophthalmoscope. Several of the newest imaging technologies may hold value to many neurodegenerative disorders besides those affecting the retina. The first is a structural technology known as optical coherence tomography. It allows each cellular layer of the retina to be visualized with 3μ axial resolution and image reconstruction. It carries applications for ocular diagnostics and therapeutic tracking, particularly for retinal ganglion cell axon loss in glaucoma and congenital X-linked retinoschisis (Apushkin et al., 2005). It also holds utility for MS by virtue of its ability to image loss of fibers in the retinal nerve fiber layer, which is a common manifestation of MS (Fisher et al., 2006).
Another new structural technology is adaptive optics. Its resolution is so great that it allows individual photoreceptors to be imaged. Pioneered by David Williams and colleagues at the University of Rochester, the technology has confirmed that human color vision depends on three color receptors—red, green, and blue cones—as first postulated in the early 1800s by Thomas Young.
A final tool is the development of metabolic biomarkers, which potentially could be localized together with structural imaging (Gu et al., 2003). Combination techniques would allow dynamic tracking of functional disruptions and pathophysiology with high resolution and in real time, said Sieving. He described an animal model in which monkeys’ retinal ganglion cells are labeled and then, after their retrograde transport, are individually visualized in the retina. He stressed the potential for overlap with other neurodegenerative diseases, pointing out, for example, that elevated level of homocysteine is a metabolic biomarker not only for age-related macular degeneration but also for cardiac disease. He ended his presentation with the message that the science is poised to take advantage of ultra-high-resolution imaging tools to develop dynamic functional markers for studying neurodegenerative retinal diseases as well as other neurodegenerative disease. The insights gained can be applied to understanding pathophysiology as well as providing outcome measures for clinical trials.