Optical coherence tomography in Alzheimer's disease

Alzheimer’s disease (AD) is a neurodegenerative disorder, which starts as mild cognitive impairment (MCI) several years before its full-blown clinical manifestation. In the last two decades, optical coherence tomography (OCT) has been used to measure a significant loss in peripapillary retinal nerve fiber layer (RNFL) and in macular thickness and volume in patients affected by a form of mild to severe dementia. These morphological abnormalities correlate to some extent with the severity of the disease as evaluated with neuropsychological tests. Furthermore, these structural measures correlate with electrophysiological parameters of pattern electroretinogram, reflecting integrity of the innermost retinal layers, but not with those of the visual evoked potentials, reflecting activity of the post-chiasmatic visual pathway. The latter evidence suggests that RNFL thickness reduction is related to neuronal degeneration in the ganglion cell layer and not to a retrograde degeneration from changes in the post-chiasmatic visual pathway. These data suggest a possible role of OCT in monitoring the progression of AD and in assessing the effectiveness of purported AD treatments.