Final answer:
Topical ophthalmic drugs are designed to penetrate the cornea through diffusion to treat conditions within the anterior chamber, but their effects on the posterior or vitreous chambers are minimal due to the nature of diffusion and selective permeability.
Step-by-step explanation:
Topical ophthalmic drugs penetrate the cornea by diffusion and tend to be absorbed into the anterior chamber having little effect in the posterior or vitreous chambers. The anterior chamber contains the aqueous humor, a watery fluid that fills the space in the eye anterior to the lens. Because diffusion is a slow process and occurs over small distances, topical ophthalmic drugs effectively reach the cornea through the thin tear layer that covers it. However, given the nature of diffusion and selective permeability, these drugs usually have limited effect on the more distant posterior and vitreous chambers of the eye.