Choroidal Thinning as a New Finding in Alzheimer's Disease: Evidence from Enhanced Depth Imaging Spectral Domain Optical Coherence Tomography

Background: The involvement of retina and its vasculature has been recently described in Alzheimer's disease (AD). However, none of the previous works have yet investigated the choroid in vivo. Objective: Spectral domain optical coherence tomography (SD-OCT) and enhanced depth imaging (EDI) technique is non-invasively used to assess choroidal thickness in patients with AD and to determine whether the peripapillary retinal nerve fiber layer (RNFL) and central retinal thickness are reduced compared to normal subjects. Methods: Forty-two eyes of 21 patients (mean age, 73.1 +/- 6.9 years) with a diagnosis of mild to moderate AD and 42 eyes of 21 age-matched control subjects (mean age, 70.3 +/- 7.3 years) were included in this prospective, cross-sectional study. All the subjects underwent neuropsychological (MMSE, ADAS-Cog, and CDR) and ophthalmological evaluation. The SD-OCT images of the choroid were obtained by EDI modality. Choroidal thickness was assessed by manual measurement. The following parameters, measured automatically by the OCT software, were also analyzed for each eye: 1-mm central subfield (CSF) retinal thickness, peripapillary RNFL thickness. Results: Choroidal thickness was significantly thinner in AD than in control eyes (p < 0.05). No difference in CSF retinal thickness was found between groups (p > 0.05). Mean peripapillary RNFL thickness in all four quadrants was similar between groups (p > 0.05). OCT measurements were not correlated with any of the tested psychometric parameters (p > 0.05). Conclusion: Compared with healthy subjects, patients with AD showed a significant reduction in choroidal thickness. Choroidal thinning may represent an adjunctive biomarker for the diagnosis and follow-up of this disease.