When we split OCI group into MCI and AD dementia groups, only total SCD-Q9 score was the independent risk factor of MCI [OR: 1.390, 95% CI: 1.232–1.568, p < 0.001], whereas carrier status of APOE ε4 did not show any relationship (p = 0.191). Here, APOE is linked to Schnyder corneal dystrophy.