The relationship between diabetic retinopathy and cognitive impairment

Recent studies have shown an increased risk for cognitive impairment and dementia in patients with diabetes. An association between diabetic retinopathy (DR) and retinal microvasculature disease and cognitive impairment has been reported as potential evidence for a microvascular component to the cognitive impairment. It was hypothesized that severity of DR would be associated with cognitive impairment in individuals with type 2 diabetes.

Three hundred eighty patients with type 2 diabetes were recruited from a population-based eye screening program and grouped by severity of DR as follows: no/mild DR (n=252) and proliferative diabetic retinopathy (PDR) (n=128). Each participant underwent psychosocial assessment; depression screening; ophthalmic and physical examination, including blood assays; and cognitive assessment with the Addenbrooke's Cognitive Examination-Revised (ACE-R), Mini-Mental State Examination (MMSE), and the Mini-Cog. General linear modeling was used to examine severity of DR and cognitive impairment, adjusting for confounders.

Severity of DR demonstrated an inverse relationship with cognitive impairment (fully adjusted R2=0.415, P<0.001). Ethnicity contributed most to the variance observed (16%) followed by education (7.3%) and retinopathy status (6.8%). The no/mild DR group had lower cognitive impairment scores on ACE-R (adjusted mean±SE 77.0±1.9) compared with the PDR group (82.5±2.2, P<0.001). The MMSE cutoff scores showed that 12% of the no/mild DR group (n=31) had positive screening results for dementia or significant cognitive impairment compared with 5% in the PDR group (n=6).

Patients with minimal DR demonstrated more cognitive impairment than those with advanced DR. Therefore, the increased prevalence of cognitive impairment in diabetes may be associated with factors other than evident retinal microvascular disease.