Minimally invasive, direct, real time measurement of drug concentration in the anterior eye

Computational modeling of intraocular drug delivery supplied by porous implants

New and efficient drug delivery to the posterior part of the eye is a growing health necessity worldwide. Current treatment of eye diseases, such as age-related macular degeneration (AMD), relies on repeated intravitreal injections of drug-containing solutions. Such a drug delivery has major drawbacks including short drug life, significant medical service, and high medical cost. In this study, we explored a new approach to controlled drug delivery by introducing unique porous implants. Our computational modeling contained key physiological and anatomical traits. Incompressible flow in a porous media field, including the sclera, choroid, and retina layers, is governed by Darcy law and the time evolution of the drug concentration was solved via three convection-diffusion equations in the three layers, respectively. The computational model was validated by established results from independent studies and experimental data. Simulations of the IgG1 Fab drug delivery to the posterior eye were performed to evaluate the effectiveness of the porous implants for controlled delivery. Overall, our results indicate that drug therapeutic levels in the posterior eye sustain for eight weeks similarly to those using intravitreal injection. We first evaluated the effects of the porous implants on the drug delivery in the posterior layers. Subsequent simulations were carried out with varying porosity values in a porous episcleral implant. We found that the time evolution of drug concentration is distinctively correlated to drug source location and pore size. A correlation between porosity and fluid properties for selected porous implants was revealed for the first time in this study.

Optical fiber-coupled ocular spectrometer for measurement of drug concentration in the anterior eye--applications in pharmaceuticals research

This paper describes in detail a novel optoelectronic system designed to measure drug absorption in the anterior segment of the eye following topical application of drug formulations. This minimally invasive measurement technique offers both a method for determining drug concentration in human eyes, and demonstrates an alternative to current testing processes in model animals, which require paracentesis of the anterior chamber of the eye. The optoelectronic technique can be used with formulations, which possess appropriate spectral characteristics, namely unique absorption or fluorescence spectra. Preliminary experiments using our measurement system have been performed in rabbit and man, where we have been successful in achieving the direct measurement of topically applied brimonidine, an alpha-2 agonist used in the treatment of glaucoma. This demonstrates the feasibility of performing real-time, in vivo testing of ophthalmic drug formulations in the eye of human test subjects. We further demonstrate the novel application of the optoelectronic system for detection of topically applied UV-absorbing compounds in rabbit cadaver eyes, with a view to evaluating potential ocular sunscreen formulations. In summary, this method can be applied for the rapid comparison of the penetration of different drug formulations into the anterior eye at greatly reduced cost and time.