Determinants of eye drop size.

Ophthalmic solutions are available for multidose or single-dose administration in a wide variety of glass and plastic dropper bottles which deliver drops with a volume between 25 and 70 microl. From a biopharmaceutical and economic point of view, however, smaller volumes of 5 to 15 microl should be instilled. In this review, the technical, pharmaceutical, and therapeutic aspects of eye drop formation and delivery are presented. The different types of containers are described and the determinants of eye drop size are discussed, such as the design and physical characteristics of the dropper tip and bottle, the physico-chemical properties of the solution, and the manner in which the patient dispenses the drops. Preferred and alternative instillation techniques and aids to facilitate the administration of eye drops by elderly patients are described.