Transcorneal Drug Absorption into the Eye

Since most eye medications need to enter the eye for a pharmacological effect, ocular drug delivery is a major issue in ocular research. Generally, three routes into the eye have been described in the literature [24]  

The transcorneal route. This is still the major pathway for ocular drug delivery, representing the direct pathway into the eye and is applicable for most of drug substances. 

If the medical drug is applied topically to the eye, another important factor for ocular drug delivery and penetration has to be taken in account that is, the precorneal clearance which rapidly reduces the drug amount available for penetration. Thus, it is a major factor to take into consideration while evaluating (transcorneal) absorption. So far, due to experimental limitations, not much thought has been given to precorneal clearance in cell-based in vitro models. 

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