SPP1 and Alzheimer disease: We found significant upregulation of OPN expression in AD retinas, quantified as fluorescence intensity over threshold in each field of view (400 μm2) (AD: 3.0 ± 0.6, n = 24/3 fields/patients) compared to age matched controls (CTRL: 0.7 ± 0.2, n = 27/4 fields/patients; p < 0.001) (Figure 5B).