Complications associated with diabetes have increased along with diabetes prevalence. Cataract in diabetic patients is a significant cause of vision loss. We aimed to investigate related factors such as comorbidities and co-medications to provide evidence for cataract prevention and management in diabetic patients. A nested case-control study was performed using the Korean National Insurance Health Service Database. Patients diagnosed with cataract after type 2 diabetes were defined as the case group and control group included patients never diagnosed with cataract. In a total of 117,610 subjects, the case group consisted of 14,352 patients after 1:1 risk set sampling. Among the covariates included in the analysis, atopic disorder was associated with increased development of cataracts in diabetes whereas dementia was associated with decreased prevalence of cataracts. Regarding dementia medications, patients with memantine and donepezil showed a significantly lowered risk of developing cataracts. The National Health Insurance System database may differ from actual medical treatment data to insurance claim date, and the effect on outcome cannot be measured due to a lack of clinical data on clinical measurement and severity. It is necessary to manage diabetic patients' comorbidities and co-medications in coordination with ocular complications.