Ocular Drug Delivery Routes: Diseases Overview and Advanced Administration Methods

The eye is anatomically divided into two: the anterior segment and the posterior segment. The anterior segment comprises structures located at the front of the eye, including the cornea, iris, ciliary body, pupil, aqueous humor, and lens. In contrast, the posterior segment encompasses structures located at the back of the eye, such as the vitreous, retina, choroid, macula, and optic nerves. Numerous diseases arise due to anomalies occurring within these ocular tissues. When formulating drugs for ocular conditions, it is crucial to consider the specific segment of the eye affected by the disease. Various routes of drug administration and dosage forms are available for delivering medications to the eye. These include topical forms such as solutions, emulsions, suspensions, ointments, and gels. Additionally, drugs can be administered through routes such as intravitreal, suprachoroidal, intracorneal, or subconjunctival. Furthermore, novel methods of drug delivery to the eye have emerged, including inserts, films, contact lenses, and microneedles. The aim of this review is to discuss innovative drug delivery systems and explain in detail the different routes of drug administration to the eye with examples from the current literature.