A new insight into retinal vein occlusion pathogenesis

Introduction
To evaluate (ex vivo) the characteristic of fibrin clotting in patients with retinal vein occlusion.

Material and methods
Fifty nine patients with a history of retinal vein occlusion were enrolled in the study. The diagnosis of retinal vein occlusion was based on the typical fundus appearance, supplemented by digital photography, fluorescein angiography, and optical coherence tomography. The control group consisted of 59 subjects matched for age, sex, body mass index, medications, and cardiovascular risk factors. The ex vivo fibrin clots obtained from citrate plasma samples from all patients were used for the measurement of clot permeation, expressed as the permeability coefficient, Ks (Darcy constant). The turbidity of fibrin clot formation, reflected by the “lag phase” of the turbidity curve and maximum absorbance at plateau (ΔAbmax), tissue-plasminogen activator (t-PA) – induced fibrinolysis characterized by maximum rates of increase in D-dimer levels (D-Drate) and maximum D-dimer concentrations (D-Dmax) were evaluated. The time required for 50% decrease in maximum clot absorption (t50%) was chosen as an additional marker of clot susceptibility to fibrinolysis.

Results
Patients with retinal vein occlusion were characterized by the unfavourable plasma fibrin clot properties. Clot permeability was 30% lower, as compared to the controls (p<0.0001), the “lag phase” was 11% shorter (p<0.0001) indicating faster fibrin formation, and the ΔAbmax was 19% higher (p <0.0001), indicating thicker fibrin fibers. The D-Dmax indicating thrombotic mass available for fibrinolytic agents was 22% higher in the RVO group (p <0.0001) and the t50% was 29% longer (p <0.0001) compared with controls. Only the D-Drate was similar in both groups (p = 0.223). The differences remained statistically significant after adjustment for fibrinogen, glucose, and platelet count.

Conclusions
The results indicate that in patients with retinal vein occlusion, less porous plasma fibrin clots composed of thicker fibrils with the reduced permeability and susceptibility to lysis are found, as compared to controls. Plasma fibrinogen and C-reactive protein levels are recognized as the most important modulators of fibrin function.