Topical administration

• Given as drops or ointment
• Required to act on surface
• Require corneal penetration

Corneal penetration

• Corneal penetration is good for low molecular weight drugs
• Outer corneal layer is mostly made up of epithelial cells - highly lipophilic, acts as barrier for hydrophilic drugs
• Inner stroma is hydrophilic - acts as a barrier for lipid-soluble drugs

• Some drugs have both lipophilic and hydrophilic properties and penetrate the cornea easily e.g. chloramphenicol
• Ocular surface inflammation can often reduce the hydrophobic nature of the endothelium
• Lipid layer of tear film may impede drug penetration

Topical steroids

• Need hydrophobic and hydrophilic capacity
• Chemical modifications to steroids alters its characteristics
  • Alcohol or acetate makes steroid more hydrophobic
  • Phosphate makes it more hydrophilic

Prednisolone acetate

• Hydrophobic
• Good penetration in uninflamed cornea
• Used post-operatively

Prednisolone phosphate