Retinal alterations in mild cognitive impairment and Alzheimer's disease: an optical coherence tomography study

Retinal nerve fiber layer thickness (RNFL) measured by means of Optical Coherence Tomography (OCT) has been used as a marker not only of ophthalmologic diseases but also of neurodegenerative diseases such as Alzheimer's disease (AD) and mild cognitive impairment (MCI). The purpose of this work was to demonstrate that patients with amnestic MCI show an intermediate RNFL thickness between normality and AD, and a macular volume and thickness as well. In a cross-sectional study we consecutively recruited 18 patients with AD, 21 with MCI, and 41 healthy controls. OCT was performed in all of them to measure circumpapillary RNFL thickness in µm, as well as macular volume and thickness. In the analysis of variance we saw that RNFL was thinner in MCI patients compared with controls, and it was also thinner in AD patients compared with MCI patients and controls. With regard to the macular measurements in mm(3), MCI patients had the greatest macular volume in comparison with AD patients and controls. In turn the controls had greater macular volume than AD patients. The decreased RNFL thickness in MCI and AD patients suggests loss of retinal neurons and their axons. The increased thickness and macular volume have never been reported before in aMCI. This finding could be explained by inflammation and/or gliosis in early stages of AD. OCT could be a useful marker of AD for early detection and monitoring progression.