Effect of microplasmin on the clearance of vitreous haemorrhage from an experimental model in rabbits

Changes in the vitreous body after experimental vitreous hemorrhage in rabbit: An interdisciplinary study

PURPOSE

To explore the changes in vitreous body after vitreous hemorrhage and assess its prognosis from the perspective of vitreoretinal interface.

METHODS

The experiment was performed on 32 New Zealand rabbits (64 eyes), weighing 2500-3000 g for 4 months and unlimited gender, which was injected with 0.2 mL of autologous blood into the center of vitreous cavity-the study group (right eyes), and the control one was treated in the same manner with equal volumes of saline. The rabbits were randomly and equally divided into the following four batches according to the days of observation: Days 3, 7, 14, and 30 after injection. IOP and severity grading were evaluated before rabbits' execution and eyeballs were enucleated. The anterior segment was separated to flow out the vitreous body naturally to detect the liquefaction degree and viscosity. Then, chemical composition of electrolytes, PCT and bFGF were determined by colorimetry and enzyme-linked immunosorbent assay (ELISA). Finally, the incidence of posterior vitreous detachment (PVD) was observed after vitreous sampled. The studies were double-blind.

RESULTS

After injection, the extent of vitreous opacity and coagulum size decreased over time. Both the degree of liquefaction and the length of tow differed significantly between two groups at different time points (all p < 0.001). The liquefaction degree in the study group rose obviously from the Day 14, which the viscosity declined significantly on the initial time. Biochemical markers fluctuated temporarily, except for basic fibroblast growth factor (bFGF), which continued to rise and was correlated with the liquefaction degree (r = 0.658, p < 0.001). Besides, the incidence of PVD increased from the 14th day (p < 0.05), and it was highly positively correlated with the number of macrophages (r = 0.934; p < 0.001).

CONCLUSION

After vitreous hemorrhage, the changes of the vitreous body are relatively minor earlier (2-4 weeks), but irreversible later. Specifically, the degree of liquefaction increases with a decrease in viscosity, and the chemotaxis of macrophages and bFGF induce incomplete PVD.

Pharmacologic Vitreolysis in Vascular Diseases of the Retina

Vascular diseases of the retina such as diabetic retinopathy and vascular occlusions account for a large proportion of visual morbidity and blindness worldwide. The role of vitreous in the pathogenesis of these conditions has been increasingly recognized. Despite advances in the surgical technique of pars plana vitrectomy, the use of intravitreal agents for the lysis of vitreous has received attention, guided largely by promising results from the trials involving patients with non-vascular retinal diseases such as vitreomacular traction. The purpose of this review is to provide a comprehensive summary of the present knowledge on pathophysiologic basis of pharmacologic vitreolysis and its efficacy in vascular diseases of the retina. A review of completed and ongoing clinical trials will be presented, along with insights into future directions of this therapy.

[Pharmacological vitreolysis]

Posterior vitreous detachment (PVD) is a physiological ageing process. In many cases PVD is incomplete and pathological adhesions of vitreous collagen may be associated with tractional forces in the periphery where they can cause retinal breaks and lead to detachment of the neurosensory retina. In the macular area such tractional forces at the vitreoretinal interface can contribute to the formation of specific entities such as vitreomacular traction syndrome and macular holes which are associated with an impairment of visual acuity and disturbing metamorphopsia. Currently, pars plana vitrectomy with induction of PVD, peeling of epiretinal membranes and the ILM represents an effective and safe treatment option for these conditions. Pharmacological vitreolysis is a new and alternative, non-surgical approach to release tractional forces at the vitreoretinal interface by injecting an enzyme with proteolytic activity against fibronectin and laminin into the vitreous cavity. Certain forms of vitreomacular traction and smaller macular holes can be successfully treated in this way without surgical manipulation of the retinal surface. The role of the concept of pharmacological vitreolysis as a treatment option even for exudative macular diseases or as an adjunct to assist vitreoretinal surgical procedures is currently under investigation.