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Lisa Pohl, Kai Januschowski, Sven Schnichels, Jose Hurst, Martin Prinz, Christine Hohenadl, Charlotte Reither, Martin Stephan Spitzer; Hydrophilic vitreous substitute based on cross- linked hyaluronate - assessment of effects on retinal function and intraocular pressureusing alternatives to animal testing . Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):5732.
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Vitreous substitutes are needed as tamponades after vitrectomy for retinal detachment. Hydrophilic biopolymers such as cross-linked hyaluronate are promising substances with the potential to overcome the drawbacks associated with current hydrophobic tamponade materials. Before a potential use in humans, biocompatibility of these hydrogels with respect to retinal function and intraocular pressure (IOP) needs to be demonstrated.
Sterilized cross-linked hyaluronate (Princess Volume, Croma Pharma, Austria) with a refractive index of 1.33 (identical to human vitreous) was injected through 23 or 20 G needles either into ex vivo vitrectomized pig eyes or on top of bovine retinal flat mounts.<br /> Using this non-animal testing strategy, hydrogel biocompatibility was evaluated by measuring the scotopic electroretinogram (ERG) of the isolated perfused bovine retina and continuously assessing the IOP in the anterior chamber of the whole pig eye.
In the experimental setup of the isolated perfused bovine retina the B wave dropped by 22% 5 min after application of the hydrogel, which had been injected during a stop of perfusion for 120 s. At the same time the A wave showed a slight increase of 5.8%. At the end of the measurement, the B wave had decreased by 7.8% (p=0,099;n=5) while the A wave revealed an increase of 13.7 % (p=0,108;n=5).<br /> <br /> In the whole eye pig model the swelling of the hydrogel caused a 9.68% increase in IOP after 24 hours which, however, was not significant (p=0,479;n=8).
According to the ERG results no negative or toxic effects with respect to retina functionality were observed in the isolated perfused retina model. The slight increase of IOP caused by hydrogel swelling is not considered a problem in clinical use and may even enhance the tamponading effect when used as a vitreous substitute. Thus, the hyaluronate hydrogel met two important criteria required for vitreous replacements. The use of the described ex vivo models will allow to reduce the number of animal experiments.
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