Diagnosis of Alzheimer's disease by analyzing the roughness of the retinal layers

Abstract

PurposeAlzheimer’s Disease (AD) is the most common cause of dementia. Retinal thickness changes had been reported in different stages of the disease, being these changes a biomarker of AD progression. There is increasing evidence that thinned and thickened regions are interspersed throughout the retinal layers of AD patients, resulting in the roughness of their bounding surfaces and thickness maps. The aim of this work is to prove the roughness of retinal layers, as assessed by the fractal dimension (FD) of their thickness maps, is an early biomarker of AD.MethodsA complete ophthalmological exam and cognitive test (Mini Mental State Examination) was carried out in 24 healthy volunteers and 19 patients with mild AD. Total retinal thickness and retinal layers thickness were studied by optical coherence tomography (OCT) and thickness retinal maps were obtained. From the whole retinal area scanned on each subject only a central square region available from all sample subjects was kept for roughness analysis. In this square, the FD of the thickness map of each retinal layer was calculated as an index of its roughness.ResultsThe FD of retinal layers is significantly higher (p < 0.05) in the AD group, compared to the healthy group. The correlation of FD with cognitive score, visual acuity and age reaches statistical significance in 7 layers. Nearly all (44 out of 45) FD correlations among layers are positive and half of them (23) reached statistical significance (p < 0.05). Factor analysis revealed two groups of retinal layers whose roughness evolves independently: the first includes two layers related to the outer segments and may be influenced by dysregulation of the choroidal vascular network; and the second includes the remaining layers, and may be associated with the inflammatory process of the retina.ConclusionsRoughness is a holistic feature of retinal layers that can be assessed by FD of their thickness maps and is an early biomarker of AD.