While eyes are amongst of the most accessible organs in a human body, several issues related to ocular physiology remain unanswered. Our group is combining mathematical modeling with In vitro and ex vivo experiments to develop an understanding of various physiological processes in the eyes and to understand factors that contribute to ‘dry eyes’, which is the most common ocular ailment, and also to develop possible treatments and efficient drug delivery vehicles.
We have developed a model for drainage of tear fluid from the eyes through the canaliculi, and have coupled this with a model for the transport of ions and water through the conjunctival epithelium. The combined model is able to predict the steady state tear film thickness, salt concentration and the electrical potential in the eye, and the dependency of these on physiological parameters such as tear secretion rates, salt concentration in the secreted tears, elastic properties of canaliculi, tear evaporation rates, etc. We also predict the dynamic tear film thickness and salt concentrations after fluid instillation, and the effect of various parameters on the rates at which the instilled tear fluid leave the eye. All the predictions are in excellent agreement with the experimental results available in literature. This model helps us understand various aspects of tear film dynamics and also helps us identify potential dry eye treatments.
Our model for tear also correctly predicts that only about 1% of the ophthalmic drugs instilled as drops enter the eyes. The other 99% of the drug enters systemic circulations and can produce toxic effects. Our group has been exploring the feasibility of entrapping ophthalmic drugs in soft contact lenses for ophthalmic drug delivery. We have demonstrated that a contact lens can deliver about 50% of the entrapped drug compared to 1% for delivery by drops. We have explored various approaches for entrapment of drugs in contact lenses such as loading by soaking, direct addition of drug in gel during polymerization, and loading the drug into nanoparticles and entrapping the nanoparticles in the gel. Direct entrapment and loading by soaking are effective means for trapping drugs but these can provide drug release only for a period of a few hours for a number of important ophthalmic drugs. However, the nanoparticle-laden contact lenses fabricated in our lab can provide drug delivery for extended period of time.
We hope that our efforts in this area will lead to significant improvements in the understanding of ocular dynamics and also help in developing new ‘dry eye’ treatments and also lead to development of contact lenses for delivery of ophthalmic drugs.