Topical Application onto the Eyelid Skin: Is it a Feasible Delivery Route of Ophthalmic Drugs?

Topical application of ophthalmic drugs remains to be the preferred delivery method. Eye drops lead the pharmaceutical forms due to ease of application. Despite the poor bioavailability of drugs administered topically, especially related to the dilution and excretion by tear fluid, the absence of controlled drug delivery, and the poor compliance within pediatric and senior populations, eye drops and ointments are still the first choices in eye--related disorders management. Only a few studies have explored the eyelid skin as a site for drug application and transdermal delivery as an alternative route of administration of ophthalmic drugs. Such works have validated the delivery of drugs into the ocular tissues through the eyelid barrier. The eyelid represents a differentiated skin barrier concerning the thickness, the structure of the stratum corneum, the vasculature, and the amount of lipids. This work intends to question why the eyelid, being an accessible, non-invasive, comfortable route of administration is not considered a feasible route for ophthalmic drugs. The eyelid structure is presented, and the anatomical and physiological distinctive characteristics are presented. The work also presents the research work on topical drug application to the eyelid skin that has been published so far.