| In recent years, most ophthalmologists have realized that the posterior vitreous plays a key role in numeous vitreoretinal diseases, and the abnormal vitreoretinal junction is the pathologic fundation of these deseases. So the atraumatic cleavage of the vitreoretinal adhesion is important in the management of these diseases. Pars plana vitrectomy is the most efficient method, but to those whose vitreoretinal adhere firmly it can not remove the cortex completely and often cause some complications. So the evaluation of various pharmacologic adjuncts, either alone or in conjunction with pars plana vitrectomy, to help with vitreoretinal separation has been the subject of numerous previous studies. Dispase is a metalloenzyme known to be a potent type IV collagenase obtained from Bacillus polymixia. The efficacy of Dispase in inducing PVD has been proved, this study is to evaluate the relationship between time , dose and efficacy, and to observe the toxicity to the retina after intravitreal injection with Dispase in the rabbit eyes.40 young New Zeal rabbits were randomized into 5 groups (8 in each group, respectively), that received 0. 006U(group A), 0.012U(group B), 0. 03U(group C), 0. 05U/0. 05ml (group D) of Dispase. Group E were injected witha volumetric equivalent dose of 0.01 M sterile phosphat-buffered saline (PBS) as control. All animals were initially examined with ophthalmoscopy to exclude any preexisting vitreoretinal abnormalities. All the eyes were used as study eye.Stock solution of Dispase at a concentration of 2. 4U/ml at - 20℃ were prepared in sterile calcium-and magnesium-free 0.01 M PBS one day before operation, then being stored at - 4℃ until further use. The animals were anesthized, 0. 05ml Dispase or PBS was injected into the midvitreous cavity. 20 rabbits (4 in each group) were killed at 15, 30, Ih, Id postoperatively, the globes were enucleated and processed for scanning electron microscopy (SEM)to determine the state of posterior vitreous cortex and for histology. The globes enucleated at 1d were also examined with transmission electronic microscope(TEM). The other 20 rabbits were examined with optical coherence tomography(OCT) at 2h, 1d and 1w postoperatively to evaluate the extent of induced PVD.To evaluate the toxicity , the 20 animals examined with OCT were also followed with ophthalmoscopy and electroretinography (ERG) up to 6w. During the period,1 animal in each group was euthansized at 1w and 4w, all the animals were euthansized at 6w postoperatively, and the globes were enucleated and examined with TEM and light microscope. Rusults (1) SEM demonstrated that PVD could not be induced in the 0. 006U group or in the PBS group; In the 0. 012U group, PVD started at 30min, partial PVD formed at 1h and complete PVD induced at 1d postoperatively; In the 0.03U group, PVD started at 15min, complete PVD induced at Ih postoperatively; In the 0.05U group, PVD started at 15min, complete PVD induced at 30min postoperatively. (2) OCT showed that 0. 006U of Dispase and PBS could not induce PVD; In the other three groups , OCT showed induced PVD in 13 eyes at 1d postoperatively: 3 in 0. 012U, 5 in 0. 03U, 5 in 0. 05U. No more PVD were found at 1w postoperatively. (3)The direct observation withophthalraoscopy observed that the eyes receiving PBS and Dispase 0. 012U had no significant change postoperatively. Preretinal or vitreous hemorrhage were found in the groups with Dispase 0. 03U. In group 0. 05U , 2 cataracts and 2 lens subluxation were found. (4) No significant changes were found in both a- and b-wave latency in The ERG. Mean a-wave amplitude of the group receiving 0. 05U of Dispase were remarkably reduced at the first week (P<0. 05), then returned to normal at the second week. Mean b-wave amplitude of all the groups receiving Dispase were remarkably reduced at 1d postoperatively (P<0. 05); the group 0. 006U and 0. 012U returned to normal within 1w; 0. 03U returned to normal during 2w; 0. 05U returned to normal till 6w postoperation. (5) No retinal damage were found in all... |
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