Hydrogel-based formulations for drug delivery to the anterior segment of the eye

The anterior segment of the eye is in peril of different injuries and diseases which could result in persistent corneal defects, opacification, and even loss of vision. Considering these disorders and diseases demanding permanent drug administration through the anterior segment of the eye, the traditional topical dosage form of target drugs such as eye drops is commonly applied. However, such drug administration seems inefficient due to quick drug evaporation and waste by blinking. Emerging advanced ocular drug delivery technologies, drug delivery systems to the anterior segment of the eye (DDASE) with increased drug retention time and bioavailability have been considered as alternative methods with high efficacy. This review summarizes recent research progress related to drug delivery systems administered on the anterior segment of the eye, with a particular focus on hydrogel-based formulations as an advanced one. Furthermore, hydrogel preparation and drug loading strategies in these systems along with their corresponding pros and cons are discussed in four groups of drugs commonly used for the treatment of disease of the anterior segment of the eye.