The purpose of this study was to generate intravitreal
plasmin after
intravitreal injection of
tissue plasminogen activator (TPA) and cryopexy, and to assess its proteolytic effect on the vitreoretinal border region.Twenty-four hr after a mild cryopexy, 25 microg recombinant
tissue plasminogen activator (TPA) was injected into the vitreous cavity, the fellow eye received an
intravitreal injection of the same volume of buffered
salt solution. Light, scanning and transmission electron microscopy was performed in 24 eyes that underwent
vitrectomy 1 week later.
Plasmin was measured prior and 2 hr after intravitreal TPA injection (4 eyes).
Hyaluronic acid (8 eyes) and
vitronectin (4 eyes) were measured 1 week after TPA- or BSS-injection and compared to untreated controls. In all eyes treated with TPA, histopathologic examination by scanning and transmission electron microscopy demonstrated a complete detachment of the vitreous from the surface of the retina as well as from the posterior surface of the lens. After BSS-injection, vitreous cortex attachment to the retina was demonstrated in all eyes. Two hr after TPA-injection,
plasmin increased to 9.75 mU ml(-1)(s.d.+/-2.3). Neither a decrease of
hyaluronic acid nor an increase of
transglutaminase, that might alter the vitreous structure leading to a collapse of the vitreous, were detected in treated eyes. There was no increase of
vitronectin indicating proliferative activity.A temporary breakdown of the blood-retinal barrier by cryopexy combined with
intravitreal injection of TPA is a sufficient technique to induce a
posterior vitreous detachment enzymatically. The method may be useful prior to mechanical
vitrectomy.