Ocular drug absorption

ocular drug absorption

Ocular drug absorption describes how medicines delivered to the surface of the eye move into eye tissues and sometimes into the bloodstream. When you put drops in the eye, the liquid first mixes with the tear film and then must cross barriers such as the cornea and conjunctiva to reach target tissues. The cornea is a key barrier: its outer layer repels water-loving molecules, while deeper layers favor lipid-soluble drugs, so a medicine's chemical properties affect how well it gets through. Tear production and blinking wash away drops quickly, which means only a small percentage of the applied dose actually reaches the intended site. Because of these challenges, many eye medicines have low usable bioavailability and need frequent dosing or special formulations like gels, ointments, or slow-release inserts. Some of the drug can also drain through the tear duct to the nose and be absorbed into the body, which may cause side effects away from the eye. Doctors and pharmacists consider absorption factors when choosing the dose, formulation, and how to advise patients to apply their medicines. Simple measures such as proper placement of drops and blocking the tear drainage can increase local absorption and reduce systemic exposure. Newer technologies aim to overcome physical barriers with nanoparticle carriers, implants, or contact-lens based delivery to improve effectiveness and convenience. Understanding how absorption works helps patients and clinicians get the most benefit from eye treatments while minimizing risks. If a medicine does not seem to be working, problems with absorption are often a reason to review technique, formulation choice, or dosing schedule.