In the past three decades, the application of nanotechnology in ophthalmology has gained considerable progress for the treatment of ocular diseases including anterior and posterior diseases. Results strongly suggest that delivery of ocular medicines, especially those based on macromolecular agents such as proteins, peptides, and nucleotides, are greatly enhanced by the use of nanotechnology. Generally, ophthalmic drugs are delivered to ocular tissues by precorneal instillation and intravitreal injections. An ideal ocular drug delivery system should have certain desirable properties, such as excellent corneal and conjunctival penetration, prolonged residence time, sustained release, and easy administration. It should also be nonirritating and noncytotoxic. This review places in perspective the importance of nanoparticles in the pharmacokinetics and disposition of ocularly administered drugs. Furthermore, the safety and compatibility of nanoparticles for ocular administration are specifically discussed.