Table 2.

Longitudinal studies assessing the glycated hemoglobin thresholds for retinopathy

Ref.	Study population characteristics	Assessment of retinopathy	Method of determining cutoff	Cut off
Tsugawa et al[48]	3 yr follow-up; number = 19987 Japanese subjects; age ≥ 21 yr; diabetes not excluded	Nonmydriatic 45° retinal photograph	Test for nonlinearity in multivariate logistic regression models with restricted cubicspline Multivariate logistic regression with categories of HbA1c as independent variable	Possible threshold at HbA1c levels between 6% and 7% 6.5%-6.9%
van Leiden et al[49] Hoorn study	7.9-11.0 yr follow-up; number = 233; age 50-74 yr; analyses in total study group and in subjects without diabetes	Ophthalmoscopy and fundus photography	Logistic model with categories of HbA1c (adjusted for age, sex, hypertension, glucose metabolism category)	No threshold found

HbA1c: Glycated hemoglobin.