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M. Vezina, M. Bussieres; Assessment of Techniques for Sub-Retinal Administration in Rabbits. Invest. Ophthalmol. Vis. Sci. 2008;49(13):5613.
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Sub-retinal administration of a therapeutic agent can be advantageous when it is desirable to localize exposure close to a discrete region of interest within the retina (as opposed to a generalized exposure from an intravitreal injection), or when a local depot delivery is required for slow release. Like intravitreal injection, it has the added advantage of bypassing the blood-retinal barrier. Several techniques were evaluated to determine a reliable method of subretinal delivery in the rabbit.
Fifteen New Zealand White rabbits underwent subretinal injections with or without partial vitrectomy. Animals were anesthetized with ketamine/xylazine and the eye exposed by a lateral canthotomy followed by retraction of the eyelids to obtain a pseudo-proptosis. Dental dam was fitted over the globe for final exposition. A topical anesthetic was applied. Hydration of the eye was maintained with a methylcellulose or balanced salt solution. The pupils were dilated and under a surgical ophthalmic microscope/BIOM, a 25G fiber optic light source was inserted for visualization of the retina. A 41G needle, connected to a microextension tube and 1cc syringe was used to administer the sub-retinal injection. The needle was passed into the eye via a 20G sclerotomy. In some animals, prior to sub-retinal injection, a partial vitrectomy was performed with the integrity of the globe maintained by a BSS+ infusion. The injections were administered in one or two phases. Either a direct 50 to 150 µL injection of methylene blue solution (for visualization) was administered to different regions of the retina, or a small saline bleb was created to cause the initial lift of the retina, followed by inflation of the bleb with methylene blue solution.
The most successful blebs were located in the vicinity of the optic disc or myelinated nerve fibers. Bleb creation was more difficult as distance from the optic disc increased. The vitrectomy did not provide any advantage for larger volumes of administration as blebs up to 150 µL were successfully created without it. Using saline to first lift the retina, provided some advantage against reflux that could occur during direct injections, however, on several occasions this method proved to be worse with the low viscosity solution that was used.
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