Purpose: To investigate the intraocular distribution kinetics of 70-kDa dextran after subconjunctival injection.
Methods: The right eye of 15 mice received a single subconjunctival injection of a 1.5-microL solution of 0.25% 70-kDa tetramethylrhodamine-dextran (TMR-D). The distribution of fluorescent labeling in eye sections was examined by fluorescence microscopy at 0.25, 1, 4, 24, or 72 hours after the injection. The brightness and homogeneity of fluorescence in the sclera, choroid, and retina were scored near the injection site, on the side of the globe opposite the injection site, and adjacent to the optic nerve head. Fluorescence intensity within the sclera and choroid adjacent to the optic nerve was assessed quantitatively by imaging densitometry.
Results: TMR-D readily diffused transsclerally and dispersed throughout a large portion of the sclera, uvea, and cornea. Shortly after the injection, homogenous fluorescence was observed in the sclera and choroid on the same meridian as that of the injection site. This fluorescence gradually decreased in intensity with distance from the injection site. At the opposite meridian, fluorescence in the choroid was more intense than in the adjacent sclera and could be traced up to the ciliary muscle. TMR-D was also observed in the retinal and optic nerve vessels. The intensity of scleral and choroidal fluorescence adjacent to the optic nerve reached a maxima at 1 hour, and then decreased slowly, with half-lives of approximately 16 and 100 hours, respectively. Visible fluorescence was maintained at least until 72 hours in the sclera, choroid, iris, and cornea. Specific fluorescent labeling was never found in the contralateral eyes.
Conclusions: Macromolecular 70-kDa dextran can be readily delivered to the mouse retina and uveal tissues by subconjunctival injection through transscleral diffusion, local hematogenous spread, and possibly movement through the uveoscleral outflow pathway. Subconjunctival injection may be a useful approach for delivering macromolecules to the retina and uvea.