We thank Wong et al. (1) for their interest in our study (2) in which we showed that retinal vessels in diabetic patients with increasing stages of diabetic retinopathy experience a continuously decreasing response to flickering light. We believe that the issue raised by Wong et al. is very important.

The study by Nguyen et al. (3) showed that arteriolar and venular calibers are structurally larger in patients with diabetes. In this study, retinal vessel diameter was measured from digital retinal photographs, a static vessels analysis.

As previous studies showed the reduced autoregulation of retinal vessels in diabetic patients without visible signs of diabetic retinopathy, we have used the provocative test with flickering light to perform a dynamic analysis of retinal vessels. In our study, the vasodilation of retinal arteries and veins decreased continuously with increasing stages of retinopathy.

Wong et al. hypothesized that pre-dilation of retinal vessels in diabetic patients may alter the response to flickering light. To prove this hypothesis, we adjusted the vasodilation for central retinal vein equivalent and central retinal artery equivalent, which were quantified in all diabetic patients and 29 healthy subjects. This analysis of our data had not been performed previously. After adjustment for age, sex, antihypertensive treatment, and central retinal artery equivalent or central retinal vein equivalent, we still observed a continuous reduction in vasodilation of arteries and veins with increasing stages of retinopathy (trend test P = 0.002 and P = 0.027, respectively). We also observed narrow arteries in severe stages of diabetic retinopathy (data not published).

We conclude that the reduced provoked vasodilation of retinal vessels may indicate an underlying pathological process and is to a certain degree influenced by baseline vessel diameter. The dilation of arteries may progress to constriction in severe stages of diabetic retinopathy. Therefore, dynamic and static analysis of retinal vessels should be combined to accurately detect and describe vascular and functional damage.

Nguyen TT, Cheung N, Wong TY: Influence of flickering light on the retinal vessels in diabetic patients (Letter).
Diabetes Care
. DOI: 10.2337/dc08-0227
Mandecka A, Dawczynski J, Blum M, Müller N, Kloos C, Wolf G, Vilser W, Hoyer H, Müller UA: Influence of flickering light on the retinal vessels in diabetic patients.
Diabetes Care
Nguyen TT, Wang JJ, Sharrett AR, Amirul Islam F, Klein R, Klein BE, Cotch MF, Wong TY: The relationship of retinal vascular caliber with diabetes and retinopathy: the Multi-Ethnic Study of Atherosclerosis (MESA).
Diabetes Care

W.V. is CIO, shareholder, and founder of IMEDOS.