[Pharmacological vitreolysis]

The vitreous plays an important role in the development and progression of vitreoretinal diseases. Vitrectomy is the treatment modality of choice in these cases. However, mechanical vitrectomy is incomplete. Therefore, alternative strategies have been pursued including pharmacological means such as enzymes. The goal of pharmacological vitreolysis is to make the surgical intervention easier and less traumatic.

Different substances have been investigated, including chondroitinase, dispase, hyaluronidase, plasmin, and microplasmin. Besides preclinical investigations, hyaluronidase and microplasmin (ThromboGenics Ltd., Dublin, Leuven) have been tested clinically. Results from the literature are reported herein.

Plasmin and microplasmin are both capable of inducing posterior vitreous detachment (PVD) in a dose- and time-dependent manner. There are no morphological or functional changes of the retina at therapeutic doses. Two phase II studies published to date demonstrate both efficacy and safety. Phase III studies are ongoing, and results are expected during 2010. Other enzymes tested show limitations in that retinal damage may occur (dispase) or liquefaction (hyaluronidase) occurs without cleavage of the vitreous cortex from the retina.

Microplasmin induces PVD. Results from clinical trials show that microplasmin helps to detach the vitreous cortex from the retina. This may be advantageous in terms of complete vitreous removal and less traumatic intervention compared to mechanical techniques, such as vitrectomy and peeling of the internal limiting membrane.