The Clinical Significance of Venous Filling Time through Panretinal Photocoagulation in Proliferative Diabetic Retinopathy

The relationship between fundus fluorescein angiographic findings and serous macular detachment in diabetic macular edema

PURPOSE

To investigate whether the serous macular detachment (SMD) shown by optical coherence tomography is associated with types of maculopathy, severity of retinopathy, the effect of macular and retinal photocoagulation, and retinal circulation times in diabetic macular edema.

METHODS

Patients were grouped as SMD+ (Group 1) and SMD- (Group 2). Fundus photography and fluorescein angiography were evaluated regarding the type of maculopathy; severity of retinopathy and also arm-retina time, arteriovenous transit time, and venous filling time; and the applied macular and panretinal laser treatment.

RESULTS

Diffuse maculopathy was seen more frequently in eyes with SMD, whereas ischemic maculopathy was more frequent in eyes without SMD. There was no significant difference regarding severity of retinopathy and retinal circulation times between groups. The frequency of patients with complete panretinal photocoagulation and grid laser photocoagulation was found to be higher in Group 2.

CONCLUSION

Serous macular detachment can occur in eyes with increased vascular permeability in macula. Serous macular detachment may be an important finding in terms of the possible existence of diffuse maculopathy and the need of additional panretinal photocoagulation, but absence of SMD may point at ischemic maculopathy.

Regulation of retinal blood flow in health and disease

Optimal retinal neuronal cell function requires an appropriate, tightly regulated environment, provided by cellular barriers, which separate functional compartments, maintain their homeostasis, and control metabolic substrate transport. Correctly regulated hemodynamics and delivery of oxygen and metabolic substrates, as well as intact blood-retinal barriers are necessary requirements for the maintenance of retinal structure and function. Retinal blood flow is autoregulated by the interaction of myogenic and metabolic mechanisms through the release of vasoactive substances by the vascular endothelium and retinal tissue surrounding the arteriolar wall. Autoregulation is achieved by adaptation of the vascular tone of the resistance vessels (arterioles, capillaries) to changes in the perfusion pressure or metabolic needs of the tissue. This adaptation occurs through the interaction of multiple mechanisms affecting the arteriolar smooth muscle cells and capillary pericytes. Mechanical stretch and increases in arteriolar transmural pressure induce the endothelial cells to release contracting factors affecting the tone of arteriolar smooth muscle cells and pericytes. Close interaction between nitric oxide (NO), lactate, arachidonic acid metabolites, released by the neuronal and glial cells during neural activity and energy-generating reactions of the retina strive to optimize blood flow according to the metabolic needs of the tissue. NO, which plays a central role in neurovascular coupling, may exert its effect, by modulating glial cell function involved in such vasomotor responses. During the evolution of ischemic microangiopathies, impairment of structure and function of the retinal neural tissue and endothelium affect the interaction of these metabolic pathways, leading to a disturbed blood flow regulation. The resulting ischemia, tissue hypoxia and alterations in the blood barrier trigger the formation of macular edema and neovascularization. Hypoxia-related VEGF expression correlates with the formation of neovessels. The relief from hypoxia results in arteriolar constriction, decreases the hydrostatic pressure in the capillaries and venules, and relieves endothelial stretching. The reestablished oxygenation of the inner retina downregulates VEGF expression and thus inhibits neovascularization and macular edema. Correct control of the multiple pathways, such as retinal blood flow, tissue oxygenation and metabolic substrate support, aiming at restoring retinal cell metabolic interactions, may be effective in preventing damage occurring during the evolution of ischemic microangiopathies.