Retinal Vascular Caliber and Risk of Retinopathy in Young Patients With Type 1 Diabetes

Alibrahim E, Donaghue KC, Rogers S, Hing S, Jenkins AJ, Chan A, Wong TY. Ophthalmology. 2006;113:1499-1503.

In the Diabetes Control and Complications Trial, 10% of patients with good glycemic control (A1C ≤6.87%) developed diabetic retinopathy (DR), but 43% of patients with poor glycemic control (A1C ≥9.49%) did not. This suggests that although A1C is an important predictor for the incidence and progression of DR, it does not fully explain the risk. In adults, retinal vascular caliber measured from fundus photographs has been associated with the risk of DR, diabetic nephropathy, and cardiovascular mortality. The Wisconsin Epidemiologic Study of Diabetic Retinopathy showed that larger arteriolar and venular calibers (AC and VC, respectively) predicted the progression of DR and the incidence of proliferative diabetic retinopathy (PDR) but not the incidence of nonproliferative diabetic retinopathy (NPDR). The purpose of this Australian case-control study was to determine whether similar associations between retinal vascular caliber and DR risk exist in children and adolescents with type 1 diabetes.

Cases and controls were identified from among 668 patients, ages 12-20 years, who had had a baseline retinal exam between 1990 and 2002; there were 172 patients who developed DR in this cohort who had had at least 1 follow-up retinal exam before age 20. Age- and gender-matched controls (n = 180) were randomly selected from among patients who did not develop DR after at least 2 years of follow-up (3 clinic visits). The median follow-up times for cases and controls were 3.1 years and 3.6 years, respectively. Retinal vascular caliber was assessed from 7-field stereo fundus photographs taken according to the Beaver Dam Eye Study protocol, which takes into account variations in AC and VC with the pulse,1 and graded according to Early Treatment Diabetic Retinopathy Study standards. AC, VC, and the ratio of AC to VC (A:V) were calculated for both eyes of all patients. Baseline photographs from 21 patients were ungradable, so results were computed from 166 cases and 165 controls. Cases and controls did not differ by any clinical parameter at baseline. Baseline A1C was slightly higher in cases (8.7 ± 1.4%) than in controls (8.5 ± 1.1%) but not significantly (P = .178). However, retinal AC was significantly larger among cases than among controls (AC = 6.3 μm, P = .004). Retinal VC was larger, but not significantly, among cases than among controls (P = .312). A:V was significantly larger in cases than in controls (0.63 ± 0.05 vs 0.61 ± 0.04, P = .011).

After controlling for age, gender, duration of diabetes, A1C, blood pressure, body mass index, and pubertal stage, the odds ratio for developing mild DR increased by 1.38 (P = .014) and 1.44 (P = .006) for each standard deviation increase in A:V and AC, respectively. No cases developed moderate or severe NPDR or any PDR. There was considerable overlap of retinal vascular caliber measurements between cases and controls; however, if these results are supported by future studies, patients with a large AC may be referred for more frequent retinal exams and more aggressive management of other risk factors for DR. These measures might include a lower A1C target.

Reference

1. Wong TY, Knudtson MD, Klein R, et al. Computer-assisted measurement of retinal vessel diameters in the Beaver Dam Eye Study: methodology, correlation between eyes, and effect of refractive errors. Ophthalmology. 2004;111:1183-1190.