A formulation for an eye treatment includes a photosensitizer and a permeability enhancing composition. The permeability enhancing composition includes one or more permeability enhancers. The permeability enhancing composition has a hydrophilic and lipophilic balance increases a permeability of an area of the eye for the photosensitizer. The hydrophilic and lipophilic balance can be characterized by a Hydrophile-Lipophile Balance (HLB) number. For example, the area of the eye may include a corneal epithelium, the photosensitizer may include riboflavin, and the permeability enhancing composition may have a corresponding HLB number between approximately 12.6 and approximately 14.6.
