In order to maximize drug penetration through the cornea, an ophthalmic drug or its vehicle should possess which property?

Lipid solubility is essential for maximizing drug penetration through the cornea because the corneal epithelium is primarily composed of lipid-rich layers. For a drug to effectively permeate this barrier, it must be able to dissolve in the lipid components of the epithelium. Lipophilic drugs are able to integrate into these lipid layers, facilitating transcellular passage and improving overall absorption.

In contrast to lipid solubility, high pH may alter the ionization of a drug but does not directly enhance its capacity to penetrate the corneal tissues. High alcohol content can provide some penetration enhancements due to its ability to disrupt lipid layers, but excessive amounts may also lead to instability or irritation. A highly polar component can hinder penetration, as polar substances do not easily cross lipid membranes. Thus, lipid solubility is the key characteristic needed for effective drug delivery in ophthalmic formulations.