Neurocognitive Assessment and Retinal Thickness Alterations in Alzheimer Disease: Is There a Correlation?

BACKGROUND: The relation of retinal thickness to neuropsychological indexes of cognitive impairment in patients with Alzheimer disease (AD) remains an area of investigation. The scope of this investigation was to compare volume and thickness changes of neuronal retinal layers in subjects with AD with those of age-matched healthy controls and to estimate the relation between cognitive functioning evaluated by neuropsychological assessment and thickness changes of the retina.
METHODS: This was a prospective single-site study where we evaluated 25 subjects with probable AD matched for age, sex, and education to 17 healthy control subjects (HC). All participants underwent a full medical evaluation, neuropsychological assessment, and optical coherence tomography (OCT) to evaluate the peripapillary retinal nerve fiber layer (pRNFL) thickness, ganglion cell complex (GCC) thickness, and macular volume.
RESULTS: The pRNFL thickness of AD patients showed a significant overall reduction compared with healthy controls (P = <0.0001). Furthermore, pRNFL was reduced in each retinal quadrant, particularly the inferior, nasal, and superior quadrants. GCC thickness and macular volume were reduced in AD patients in comparison with HC (P = 0.004; P = 0.001). Of particular interest was the correlation between OCT findings and neuropsychological assessment; we did not find a significant association of retinal thinning with worse MMSE score, but reduction of macular volume was associated with worse constructional praxis performance. Impairment of semantic-lexical and processing speed was associated with attenuation of macular GCC thickness.
CONCLUSIONS: OCT can show early thickness changes in AD patients with subtle memory disturbances. These results suggest that correlations between retinal thinning and cognitive performance warrant further investigation.