MRI study of subconjunctival and intravitreal injections.

Previous magnetic resonance imaging (MRI) studies to investigate the routes of penetration and barriers in ocular delivery have provided insights into the mechanisms of transscleral and intraocular drug delivery. The objective of the present study was to investigate ocular penetration and clearance after subconjunctival and intravitreal injections using a contrast agent at concentrations higher than those in the previous studies. This high concentration approach was hypothesized to allow the visualization of the contrast agent in the eye that could not be achieved previously. Subconjunctival and intravitreal injections of contrast agent Magnevist, a model hydrophililc probe, were performed in rabbits, and the distribution and clearance of the probe after the injections were examined by MRI. After subconjunctival injection in vivo, significant contrast agent penetration into the anterior chamber was observed but not into the vitreous. A clearance pathway of the hydrophilic probe from the subconjunctival depot to the regions near the periocular fat behind the eye was found. After intravitreal injection in vivo, the contrast agent was observed in the anterior chamber, optic nerve, and tissues surrounding the eye during clearance. MRI continues to provide insights into the transport barriers and clearance pathways of hydrophilic molecules in ocular delivery.