Analysis of optic disk color changes in Alzheimer's disease: a potential new biomarker

In the present study, we evaluated changes in the retinal nerve fiber layer (RNFL) and optic disk color (i.e., the level of paleness as an indirect sign of axonal loss) in patients with Alzheimer's disease (AD) compared with healthy controls. The usefulness of this method as a new biomarker for AD was also evaluated.

Fifty-six patients with mild or moderate AD and 56 sex-and age-matched healthy subjects were included in this cross-sectional study. All subjects underwent a complete neuro-ophthalmologic examination, including analysis of the RNFL thickness with Cirrus optical coherence tomography (OCT). One photograph of the optic disk was obtained using a Canon CF 60 DSi retinograph, and new colorimetric analysis software (Laguna ONhE) was used to detect color changes in the photographs based on hemoglobin (Hb) values as reference pigment.

Mean Hb percentage and Hb content in the outer ring, which corresponds with the neuroretinal rim, calculated by the Laguna ONhE program were significantly lower in AD patients than in healthy controls (P<0.005). OCT measurements revealed that the mean RNFL thickness was significantly decreased in AD patients compared with healthy controls (P<0.003).

Analysis of the optic disk color assessed by Laguna ONhE software revealed papillary paleness due to axonal loss and perfusion alterations, even in the early stages of AD. Application of this simple method in routine clinical practice may provide a good biomarker of AD.