How is the corneal stroma classified in terms of lipophilicity?

The corneal stroma is classified as hydrophilic primarily due to its composition, which largely consists of water and collagen fibers. The stroma is about 78% water and contains glycosaminoglycans (GAGs) such as keratan sulfate and dermatan sulfate, which are hydrophilic in nature. This high water content facilitates the diffusion of nutrients and ions, which are crucial for maintaining corneal transparency and overall eye health.

The presence of collagen and other matrix components in the stroma also contributes to its hydrophilic characteristics, as these structures can interact with water molecules and help maintain the stroma's hydration state. This property is significant when considering how drugs and other substances behave when administered topically to the eye. Hydrophilic compounds diffuse more readily through the stroma compared to lipophilic substances, which prefer a lipid-rich environment.

In contrast, lipophilic materials do not easily mix with or penetrate water-dominated environments like the stroma, making it challenging for such substances to effectively penetrate this layer. Therefore, classifying the corneal stroma as hydrophilic aligns with its physiological and structural properties, as well as its functional roles in the eye.