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Damian E. Berezovsky, Samirkumar R. Patel, Bernard E. McCarey, Hans E. Grossniklaus, Mark R. Prausnitz, Henry F. Edelhauser; In Vivo Evaluation of Fluorescent Microparticles Injected in the Rabbit Suprachoroidal Space Using Hollow Microneedles. Invest. Ophthalmol. Vis. Sci. 2011;52(14):2058.
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Particles up to 500nm have been delivered to the suprachroidal space (SCS) of the rabbit eye using hollow microneedles. The purpose of this study was to deliver a suspension of 1µm and 10µm fluorescent particles into the SCS of live rabbits, and to confirm their presence using fluorophotometry, fundus photography and histology.
Four NZW rabbits received a 100µL suprachoroidal injection of 1µm or 10µm fluorescent polystyrene particles (FluoSpheres®,Invitrogen). Injections were performed using a 1mL syringe and a hollow metal microneedle, 700-800µm in length, inserted 5mm posterior to the limbus. Intraocular fluorescence was measured using a fluorophotometer before and after injection, then weekly through 2 months. Fundus photographs (color and fluorescence) were obtained from both eyes 2 months after injection. Eyes were subsequently enucleated and submitted for routine histology.
All injections were well tolerated without complications. Baseline retina/choroid fluorescence (expressed as ng/mL fluorescein) was 8.9±2.1 ng/mL for all rabbits. Immediately following injection, retina/choroid fluorescence rose to 4237 ng/mL and 7287 ng/mL (1µm particles), and 327 ng/mL and 382 ng/mL (10µm particles). These levels were maintained through 2 months. Color fundus photography 2 months after injection revealed normal-appearing fundi in all eyes, with no signs of scarring or damage. On fluorescence imaging, eyes injected with 1µm particles showed diffuse fluorescence throughout the posterior fundus, visible behind the choroidal vasculature. Eyes injected with 10µm particles showed a mottled pattern of fluorescence throughout the posterior fundus. Histological examination confirmed the presence of microparticles within the SCS and choroid.
This study demonstrates successful delivery of 1µm and 10µm fluorescent particles to the rabbit SCS, using a hollow metal microneedle technique. Once injected, these particles can be found throughout the posterior SCS and choroid, remaining in this location for 2 months. Normal appearance of the fundus 2 months after injection suggests that suprachoroidal injection is well suited for the delivery of microparticles for sustained drug release.
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