Vitreous humor: composition, characteristics and implication on intravitreal drug delivery.

Intravitreal administration of drug molecules is one of the most common routes for treating posterior segment eye diseases. However, the properties of vitreous humour changes with the time. A number of ocular complications such as liquefaction of the vitreous humour, solidification of the vitreous humour in the central vitreous cavity and detachment of the limiting membrane due to the shrinking of vitreous humour are some of the factors that can drastically affect the efficacy of therapeutics delivered via intravitreal route. Although significant research has been conducted for studying the properties of vitreous humour and its changes during the ageing process, there have been limited work to understand the effect of these changes on therapeutic efficacy of intravitreal drug delivery systems. In this review, we plan to discuss the biological composition and biomechanical properties of vitreous humour, methods to study the properties of vitreous humour and the changes in these properties and their relevance in ocular drug delivery field. We aim to provide a useful insight into these aspects which can aid the process of development of novel intravitreal drug delivery systems.