Differential vitreous dye diffusion following microplasmin or plasmin pre-treatment

Injectable PTHF-based thermogelling polyurethane implants for long-term intraocular application

BACKGROUND

Hydrogels show great potential to be used for intraocular applications due to their high-water content and similarity to the native vitreous. Injectable thermosensitive hydrogels through a small-bore needle can be used as a delivery system for drugs or a tamponading substitute to treat posterior eye diseases with clear clinical potential. However, none of the currently available thermosensitive hydrogels can provide intraocular support for up to 3 months or more.

METHOD

In this study, an injectable polytetrahydrofuran (PTHF)-based thermosensitive hydrogel was synthesized by polyurethane reaction. We examined the injectability, rheological properties, microstructure, cytotoxicity, and in vivo compatibility and stability of the hydrogels in rabbit eyes.

RESULTS

We found that the PTHF block type and PTHF component ratio could modulate thermogelation properties of the polyurethane polymers. The PTHF-based hydrogel implants retained normal retinal structure and function. Incorporating bioinert PTHF generated highly biocompatible and more stable thermogels in the vitreous cavity, with gel networks and the presence of polymer still observed after 3 months when other thermogels would have been completely cleared. Moreover, despite lacking hydrolytically cleavable linkages, the polymers could be most naturally removed from the native vitreous by bio-erosion without additional surgical interventions.

CONCLUSION

Our findings suggest the potential of incorporating hydrophobic bioinert blocks to enhance the in vivo stability of supramolecularly associated hydrogels for long-term intraocular applications.

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

PURPOSE

Microplasmin is known to alter the structure of the vitreous gel. The current experiments were designed to assess its ability to enhance clearance of an experimentally induced vitreous haemorrhage, and to compare it to ovine hyaluronidase.

METHODS

Twenty-five rabbits were used for this experiment, divided into five groups; groups 1-3 are microplasmin-treated eyes with 25, 75 and 125 μg, respectively. Group 4 treated with 55 IU of hyaluronidase, while group 5 was treated with normal saline (control). Eyes were injected in the mid-vitreous with 0.05 ml of autologous blood obtained from the marginal ear vein. One week later, all the groups were injected with the test solution injected in mid-vitreous as stated above. Clearance of the vitreous haemorrhage was assessed weekly indirect ophthalmoscopy for 8 weeks.

RESULTS

Microplasmin-treated eyes showed a significant clearance of the vitreous haemorrhage in a dose-dependent fashion, where group 3 (125 μg) had the highest clearance rate in comparison with control eyes. Hyaluronidase-treated eyes showed a similar clearance rate as group 3. In addition, group 3 showed a complete posterior vitreous detachment, which did not develop in hyaluronidase-treated eyes.

CONCLUSION

Microplasmin may be a useful agent to accelerate the clearance of vitreous haemorrhage.

Anatomic and pharmacokinetic properties of intravitreal bevacizumab and ranibizumab after vitrectomy and lensectomy

PURPOSE

To determine the anatomic characteristics and pharmacokinetic properties of intravitreally placed bevacizumab and ranibizumab after pars plana lensectomy or pars plana vitrectomy and to compare these with nonoperated control eyes in a rabbit model.

METHODS

Three groups of six Dutch-belted rabbits each underwent pars plana vitrectomy, pars plana lensectomy, or served as nonsurgical controls. Twelve days after surgery, 3 rabbits from each group underwent intravitreal injection in one eye with 1.25 mg/0.05 mL I-124-bevacizumab or 0.5 mg/0.05 mL I-124-ranibizumab. Serial imaging with integrated positron emission and computed tomography (PET/CT) were obtained on Days 0, 2, 5, 7, 14, 21, 28, and 35. Measured radioactivity emission in becquerels/milliliter was used to calculate the half-lives for each agent.

RESULTS

The intravitreally placed radiolabeled agents were contained within the vitreous cavity for the duration of the study. The average clearance half-lives with standard error for bevacizumab and ranibizumab after correction for radioactive decay were, respectively, 4.22 ± 0.07 days and 2.81 ± 0.05 days in unoperated eyes, 2.30 ± 0.09 days (P < 0.0001) and 2.13 ± 0.05 days (P < 0.0001) after vitrectomy, and 2.08 ± 0.07 days (P = 0.0001) and 1.79 ± 0.05 days (P < 0.0001) after lensectomy.

CONCLUSION

Intravitreal retention was longer for bevacizumab than ranibizumab within all study groups and was significantly reduced after vitrectomy and lensectomy for both agents. Consideration for more frequent intravitreal anti-vascular endothelial growth factor dosing regimens may be made for patients whose treated eyes have undergone previous vitrectomy or who are aphakic.