About 17 percent of Americans 40 or older have some degree of cataracts in one or both eyes. That number increases to almost 50 percent of adults at the age of 80. A 2010 World Health Organization report says cataracts are the cause of 51 percent of blindness around the globe, or roughly 20 million people.

For more than 2,000 years, the treatment of choice has been surgical removal of the cloudy lens of the eye.

But researchers at the University of California in San Diego have developed eyedrops that may eradicate the majority of cataracts without requiring invasive surgery. The researchers have tested their steroid-based drops on a variety of laboratory animals and have obtained encouraging results, even though the scientists are not completely sure why the drops work. The next step is to get those tests into the human population.

Medical scientists know what cataracts are: a glob of abnormal proteins that cloud the clear lens inside the eye. They also know the symptoms of a cataract: blurriness, the appearance of halos around bright lights and lack of distinct colors. They just don't fully understand why they form in the eyes of some people and not in the eyes of others. Age certainly plays a part — it's rare for children and young adults to have cataracts. External factors such as radiation, trauma and some medications seem to lead to a higher population of people with cataracts.

Historically, surgery has been the sole method of treatment of cataracts. As far back as 30 C.E. Roman writer Aulus Cornelius Celsus mentioned eye surgery in his seminal book "De Medicinae."

More recently, surgery became easier and more successful. In the 1940s, Sir Nicholas Harold Lloyd Ridley of England successfully implanted a synthetic lens to replace the affected natural lens. In the 1960s, American opthomalogist Charles D. Kelman began using a method that uses ultrasonic waves, a process called phacoemulsification, to break up the cataract before an artificial lens is placed in the eye.

Whereas cataract surgery previously required a hospital stay, current surgical methods are done on an outpatient basis and follow the same basic technique. A small incision is made in the side of the eye followed by sucking the clouded lens out of the eye itself. Then the artificial lens, in a shape similar to that of a burrito, is inserted. The lens unfolds itself to take the same space as the natural lens and then anchors itself into place. This is currently the standard method, and recent science has developed three different types of artificial lenses.

A monofocal lens is the most common. It allows the patient after surgery to see clearly at one pre-determined distance: near vision (reading or knitting), intermediate vision (working at a computer or reading a car’s dashboard) or distance vision (anything farther away). Glasses or contact lenses may be needed for the two distances that were not chosen.

Toric lenses are implanted the same way as monofocal lenses, but are also able to correct a patient’s astigmatism (an irregular curvature of parts within the eye). Again, glasses or contacts may be necessary for objects at other distances.

Multifocal lenses are, as the name implies, able to provide clarity to objects near, intermediate or distant.

A hybrid of toric and multifocal lenses is currently awaiting final FDA approval.

The future of the surgery and any of these lenses, however, may be made obsolete by the development of those UC San Diego eyedrops.