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Bryce Chiang, Yoo Chun Kim, Mark R Prausnitz; The long posterior ciliary arteries block circumferential flow in the suprachoroidal space of the rabbit eye. Invest. Ophthalmol. Vis. Sci. 2014;55(13):484.
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A microneedle injection into the suprachoroidal space (SCS) uses a ~750 µm-long hollow needle to penetrate the sclera and deposit particles in the SCS. This technique allows for increased bioavailability at sites of action in the choroid and retina and possibly fewer ocular side effects. Previous studies have shown anisotropic spread around the injection site. We hypothesize that there are anatomical barriers that prevent circumferential flow in the SCS of rabbits.
In each experiment, a 33-gauge 750 µm-long microneedle was used to inject 50 µL of fluorescent particles into the SCS of an ex vivo rabbit eye, unless otherwise specified. After waiting 1 min, the eye was snap frozen and cut into 8 scleral petals. Fluorescent images of each eye were acquired and ImageJ was used for analysis. To determine the location of the barrier, injections 3-5 mm posterior to the limbus were made at the following locations: (A) superior, (B) supratemporal, (C) temporal, superior to the long posterior ciliary artery (LPCA), (D) temporal, inferior to the LPCA, (E) infratemporal, and (F) inferior. To determine the extent of the barrier function of the LPCA, intraocular pressure (IOP), injection volume, and particle size were varied. Injections were made either (A) superior or (C) temporal above the LPCA.
Injections made superior to the LPCA (i.e., Figure 1A, B and C) resulted in particle deposition only in the superior hemisphere. Likewise, injections made inferior to the LPCA (i.e., Figure 1D, E and F) resulted in particle deposition only in the inferior hemisphere. Changes in IOP, injection volume, and particle size did not change this pattern.
Particles and dyes injected superior to the LPCA are deposited in the superior hemisphere only, and vice versa, which indicates that the LPCAs served as a barrier to circumferential spread in the SCS. Ongoing studies will correlate this result in porcine and human cadaver eyes.
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