Ophthalmic drug delivery has always been a challenge for ophthalmologists and scientists from a variety of disciplines. It is estimated that the bioavailability of ophthalmic drugs is uncertain and is about 5% or less. This is a consequence of anatomical and physiological barriers, including tear drainage and epithelial transport limitations. Unique static and dynamic eye barriers exclude the penetration of xenobiotics and discourage the active absorption of therapeutic agents. Designing an ideal delivery regimen should involve increased bioavailability and controlled drug release at the target tissue, overcoming the ocular barriers.
Eye medications administered in the conventional form of eye drops or ointments are often characterised by low bioavailability. In addition, they require repeated daily administration, which, combined with low patient compliance, causes doses to be avoided or administered incorrectly, contrary to therapeutic recommendations. Attempts to increase the bioavailability of ophthalmic medicines by using various modern solutions such as viscous solutions, suspensions, emulsions, ointments, gels, polymer inserts, and colloidal systems are still unsatisfactorily challenging in pharmaceutical research. Hence, the use of contact lenses as drug delivery systems has been increasingly explored in recent years.
The main objectives for the development of DCR (drug-controlled release) based on SCLs (soft contact lenses) are:
to increase the drug delivery efficiency;
to improve patient compliance and reduce undesirable systemic side effects, especially in chronic diseases such as glaucoma and dry eye;
to enhance SCLs tolerance, particularly in patients affected by dry eye syndrome and ocular allergies;
to design “bandage contact lenses” modified with antimicrobial or anti-inflammatory agents for managing corneal wound healing.