References (location) | Study design | Study sample | Age (years at baseline) | Assessment of retinal microvascular abnormalities | Cognitive measure and outcome | Key findings | Comments and quality rating* |
Ferguson et al20 (UK) | Cross-sectional | Clinic-based 74 men and women, with type 1 diabetes | 20–45 | Ophthalmoscopic and photographic assessment for retinal microaneurysms (MA, two or more in one eye) | WAIS-R (PC, BD, OA and DSS) | Z score in subjects with MA versus without | MA related to poorer cognitive measures on two of four tests of performance IQ (BD, DSS), information-processing speed and attention/concentration |
Cognitive and retinal assessments undertaken simultaneously | Classified as present versus absent | IT and CRT (ms) | PC: −0.13 vs 0.07, p = 0.39 | Hypertension, prevalent neuropathy, microalbuminuria, advanced retinopathy, CNS disease, alcohol or drug abuse excluded | |||
VFT | BD: −0.55 vs 0.32, p<0.01 | Adjustment for severe hypoglycaemia exposure, gender, premorbid IQ and duration of diabetes; 8/9 | |||||
PASAT (2 s errors) | OA: −0.13 vs 0.07, p = 0.44 | ||||||
DSS: −0.28 vs 0.19, p = 0.04 | |||||||
IT: 0.29 vs −0.15, p = 0.03 | |||||||
CRT: 0.44 vs −0.23, p = 0.003 | |||||||
VFT: 0.07 vs −0.04, p = 0.72 | |||||||
PASAT: 0.30 vs −0.16, p = 0.03 | |||||||
Ryan et al18 (US) | Prospective cohort | Clinic-based 103 men and women, with type 1 diabetes | 40 | Photographic grading of proliferative retinopathy (PDR) | Digit Vigilance Test, DSS, GPT, Part B of the Trail Making test | Z change score over 7 years from baseline in subjects with | PDR related to greater decline in cognitive measures of psycho-motor efficiency |
Cognitive function measured at baseline and after 7 years; retinopathy assessed at baseline and biennially | Classified as present versus absent | A composite Z score derived from the four tests | (1) PDR at baseline versus without (at both time points) −0.50 vs −0.22, p<0.02 | Alcohol or drug abuse, head trauma, PD excluded | |||
(2) Incident PDR (follow-up) versus without (at both time points)−0.56 vs −0.22, p<0.02 | Adjustment for incident (AN, DSP, ON, CAD, PVD), SBP, and duration of diabetes; 7/11 | ||||||
Kadoi et al19 (Japan) | Prospective cohort | Hospital-based 180 men and women with type 2 diabetes scheduled for CABG surgery | 64 (SD 11) | Ophthalmoscopic grading of retinopathy | Mini-Mental State Examination, Rey auditory verbal learning test, GPT, Part A of the Trail Making test, Part B of the Trail Making test, Digit Span Forward | OR for cognitive impairment in subjects with retinopathy versus without at 7 days: 2.0 (95% CI 1.3 to 3.0) p = 0.01; at 6 month: 2.1 (95% CI 1.2 to 2.7) p<0.01; at both: 2.4 (95% CI 1.4 to 2.9) p<0.01 | Retinopathy related to an increased risk of short- and long-term cognitive impairment after CABG surgery |
Cognitive function measured preoperatively and at 7 days and 6 months after surgery; retinopathy assessed preoperatively | Classified as present versus absent | Cognitive impairment defined as a decline from preoperative testing of more than 1 SD on at least 2 of the six tests | PD, renal or active liver disease, type 1 diabetes excluded | ||||
Adjustment for AAA, hypertension, HbA1c, insulin therapy, Svo2 less than 50% of time; 8/11 |
*Bold numbers indicate the quality rating.
AAA, ascending aorta atherosclerosis; AN, autonomic neuropathy; BD, block design; CABG, coronary artery bypass grafting; CAD, coronary artery disease; CI, confidence interval; CRT, choice reaction time; DSP, distal symmetric polyneuropathy; DSS, Digit Symbol Subtest; GPT, Grooved Pegboard Test; HbA1, glycosylated haemoglobin; IT, inspection time; OA, object assembly; ON, overt nephropathy; OR: odds ratio; PASAT, Paced Auditory Serial Additional Task; PC, picture completion; PD, psychiatric disorder; PVD, peripheral vascular disease; SBP, systolic blood pressure; Svo2, jugular venous oxygen saturation; VFT, Verbal Fluency Test; WAIS-R, Wechsler Adult Intelligence Scale—Revised.