LOCAL APPLICATION
Local application of drugs for the treatment of superficial eye diseases is a very satisfactory route. When the desired site of action of the drug is inside the eye then the problems of ocular barrier arises.
Corneal Barrier
For practical purposes cornea can be considered to consist of three layers. The outer and inner layers. The epithelium and the endothelium prevent water soluble agents, e.g. ionised molecules passing into the eye, but permit the passage of lipid soluble agents whereas the corneal stroma resists the passage of lipid soluble agents but freely allows the passage of water soluble agents.
Drugs with dual capability are usually capable of changing from lipid solubility to water solubility of ionisation. The effectiveness of corneal barrier may be considerably reduced by damage to the corneal epithelium.
Scleral Barrier
The sclera, unlike cornea, does not act as a differential solubility barrier and is relatively porous. However, there is unidirectional flow across the sclera from inside to outside of the eye. The intraocular pressure may be partially responsible for this.
OPTOMETRY-SHARP VISION
Optometrist