Ocular Drug Delivery
Barriers, formulations, implants, and PLGA — delivering drugs to the eye
Ocular drug delivery presents unique challenges due to the anatomical barriers of the eye. The cornea, tear film, and aqueous drainage system limit drug penetration and contact time. Understanding these barriers and the strategies used to overcome them is central to effective prescribing and counselling for eye conditions.
Why Ocular Drug Delivery is Challenging
The eye has multiple protective barriers that limit drug absorption. The cornea — with its lipophilic outer layer and hydrophilic stroma — blocks most drugs from penetrating effectively. Tear film turnover through blinking washes approximately 80% of a topical eye drop away within 5–15 minutes, meaning only a small fraction of the instilled dose reaches the target tissue.
Strategies to Overcome Ocular Barriers
To overcome these barriers, several strategies are used: prodrugs (such as latanoprost) are formulated to be more lipophilic for better corneal penetration and are converted to the active drug inside the eye; viscosity enhancers and gels prolong contact time; and intravitreal injections or implants bypass all anterior barriers to deliver drug directly to the posterior segment.
Optometrists and Ocular Prescribing
Optometrists play an important role in ocular prescribing. Depending on their registration level and qualifications, they may supply medicines under a range of legal classifications — from general sales list (GSL) to prescription-only medicines (POM) — and may work as independent or supplementary prescribers. Pharmacists should understand both the formulation choices and the prescribing rights relevant to ocular medicines.