Fig. 3

Ocular barriers to drug delivery: (a) the tear film is consist of the mucin, aqueous, and lipid layers; (b) the corneal layer is composed of the endothelium, Descemet’s membrane, stroma, Bowman’s membrane, and epithelium; (c) the conjunctival barrier; (d) the blood-aqueous barrier begins at the ciliary body stroma and is formed by the basement membrane, pigmented and non-pigmented cells and is specified with the basement membrane; (e) the blood-retinal barrier is composed of Bowman’s membrane, RPE, photoreceptors, horizontal cells, bipolar cells, amacrine cells, and the retinal ganglion cells [26]