Following adjustments for age, gender, education, vascular risk factors (including hypertension, diabetes mellitus, hyperlipidemia, and smoking), as well as accounting for intereye dependencies, the outcomes of the subgroup analysis indicated the following: in the NCI group, no significant differences (p > 0.05) in microvascular densities were observed between APOE ε4 carriers and APOE ε4 non-carriers; conversely, within the CI group, APOE ε4 carriers exhibited notably reduced densities in SVC (p = 0.006) and DVC (p = 0.048) when compared to non-carriers. Here, APOE is linked to diabetes mellitus.