How do contact lenses work

Our eyes are simply amazing. Scientists estimate that the human eye can see over ten million colors, and distinguish between 1 million of them. Now, color is really nothing more that the brain’s interpretation of light of a certain wavelength. The human eye can only detect light with a wavelength between 380 nanometers and 740 nanometers.

Our eyes have cells called rods and cones which allow us to see the way we do. The cones can detect three kinds of light, red, blue and green – all the colors that we see are combinations of these three. Because of this, the average human being is a trichromat. New research shows, however, that some women have cones that can see a fourth color, a kind of orange. These women are known as tetrachromats, and they perceive depth and texture a lot better than most normal humans.

These women are lucky. A high percentage of normal people need vision correction at some point in their lives. That is why spectacles were around for a long time; no one knows who invented them, but it is generally agreed that wearable spectacles originated from Italy, Florence, at around the 1280s. Since then spectacles have been used widely all over the world. In 1784, Benjamin Franklin invented the bifocals.

The problem with spectacles was that they were associated with age, and many people did not like to advertise that their vision was faulty. In 1887, Adolf Flick invented the glass contact lenses. They were a far cry from the comfortable, easy-to-apply contact lenses we have today; however, people like the idea, and a market for contact lenses grew.

Nowadays, the typical contact lens is made from soft, transparent plastic which molds to the shape of the eye. These plastic disks are designed to fit over the cornea, that is, the tough outer layer of the eye. The inner part of the disc aligns perfectly with the curve of the cornea. The outer part is shaped to work like a pair of spectacles – to correct the user’s vision.

The cornea is tough and is not damaged by the plastic lens. The lens does not fall out because there is a layer of moisture under the lens which keeps it sticking to the cornea. The eyelids also help to keep them in place, but they do a far more important job – keeping the eye clean under the lens. Every time the user blinks, the eyelids move the lenses slightly. This keeps the lenses covered in moisture, and at the same time washes away dirt that may accumulate either above or below the contact lens.

Many people nowadays opt for the contact lens. Contact lenses are comfortable; people who use them hardly feel a thing after putting them on. Spectacles, while easier to put on and take off, can be a hassle. They come off and on during the day, and have to be wiped whenever they fog up. People also tend to lose them or break them, which does not happen with contact lenses.

There are several different types of contact lenses. There are disposable lenses, which are used for a day and then thrown out. Then there are the daily wear lenses which last for a year and have to be removed nightly. The special oxygen permeable lenses, also called RPGs, transmit oxygen and reduce bacteria.

Then there is the large variety of tinted contact lenses, for those who want to change their eye colour temporarily. Provided they are cleaned and maintained regularly, contact lenses are quite safe and can last a long time.

Last updated on Sep 5th, 2010 and filed under Vision Care. Both comments and pings are currently closed.

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