As of now, roughly 90% of all ocular drugs are delivered through the conduit of eye drops.  Although convenient and easy to use, eye drops are surprisingly inefficient, losing about 95% of the drug to absorption by the conjunctiva (the thin membrane that covers the inner surface of the eyelid and the white part of the eyeball) and through tear duct drainage.  This is a significant amount of drug dosage that is released into the blood stream, where it can have detrimental side effects in other places in the body.  For example, Timolol is a beta blocker that is capable of treating glaucoma by preventing the production of aqueous humor (intraocular pressure between the lens and the cornea that "inflates" the globe of the eye), thus lowering the pressure inside of the eye.  Although useful for this purpose, Timolol has several severe side-effects throughout the body, such as cardiac arrhythmias, bronchiospasms, depression, and heart failure. To better target the dosage to just the eye, it has been suggested to use particle-laden contact lenses for ocular drug delivery.  Ocular drug formulations such as Timolol can be encapsulated within microemulsion nanoparticles, then entrapped with a soft poly-2-hydroxyethyl methacrylate (p-HEMA) hydrogel contact lens.  Mircoemulsions are clear, thermodynamically stable liquid mixtures of oil, water, and surfactant.  An oil-in-water microemulsion uses the surfactant to decrease the tension between droplets of oil and the continuous water phase.  These microemulsions allow highly concentrated drugs to diffuse out of the lens allowing for long-term ocular drug delivery.  The drug diffuses from the lens into the tear layers surrounding the lens, ultimately passing into the eye.