Used for corrective as well as cosmetic reasons, contact lenses are used by millions of people world-wide, who need vision correction but do not want to stick to the boring glasses. It is a surprising fact but contact lenses have been around for thousands of years or at least, the theoretical idea of it has been. The brainchild of the Leonardo da Vinci, these corrective devices have become an inseparable part of the lives of many people today. He described and sketched the modern contact lenses way back in 1508. Although many of us might be using these lightweight and virtually invisible commercial lenses, how many us truly understand as to how they work. Here is a look at how they work to correct sight, and the types of contact lenses used.
How do Contact Lenses Actually Work?
To best understand the working of contact lenses, let us first understand the concepts of perfect and defective vision. To achieve a clear, perfect vision the light rays need to converge at the retina, that is exactly behind the eye ball. However, in case the light rays do not hit that spot on the retina, there are a number of common eye or vision defects which occur. The most common refractive errors are myopia (nearsightedness) and hyperopia (farsightedness). While people with myopia can see things clearly up close but not at a distance, those with hyperopia see things better that are at a distance than close up. The other significant vision problems are astigmatism and presbyopia. Astigmatism causes light images to focus on two separate points in the eye, due to an irregularly-shaped cornea. On the other hand, presbyopia also referred to as the aging eye', causes the eye to lose its ability, to shift focus between far and near objects.
Based on the vision problem, contact lenses are made to help focus the light directly on the retina. These thin, transparent discs are made to sit on the cornea and depending on the curvature of the lens, bend the light to whichever direction it needs to go. So while the people suffering from myopia use the 'minus' or concave lens which are thicker on the edges and thinner in the middle. The 'plus' or convex curve is recommended for people with farsightedness, and are made to be thicker in the middle and thinner at the edges. For people suffering from astigmatism, the lenses are designed to give the cornea a proper shape.
Well, the first question that came to my mind when I heard about this stuff was, how is it that you can keep on wearing lenses with any discomfort or rather without those thin discs falling off? The answer to this is quite simple, contact lenses manage to stay on due to the tear fluid and the eyelid pressure. No, you do not have to cry to keep your contact lenses on! What it essentially means is, that when the eye blinks, it provides lubrication to the cornea and acts as an adhesive for your contacts. This, combined with the pressure of the eyelids, hold the contact lenses in place.
Types of Contact Lenses
The original contact lenses were made of hard plastic which caused discomfort and required a lot of maintenance. With the introduction of soft flexible contact lenses, the entire scenario changed. Made from gel-like plastic, these lenses contained 39% to 79% of water. They were not only softer and much more comfortable to wear but with proper care they lasted longer too. Here is a list of the various types of lens available.
Corrective or Prescription Contact Lenses: The best way to correct the refractive vision disorders, corrective lenses are designed to improve vision and are usually prescribed by an optometrist.
Cosmetic Contact Lenses: A must-have for all the zombie movie lovers and those influenced by the glamorous actresses, colored contact lenses allow you to change the color of your eye to various degrees. Available for people with or without prescription needs, colored contacts are available in many hues, shades, and colors.
Disposable and Daily Wear Lenses: While disposable contact lenses have to be replaced every day, every few weeks or every few months, the daily wear lenses are to be removed nightly. The difference is due to the oxygen permeability of the lens.
Other than this, there are lenses used for therapeutic reasons, like protecting an injured or diseased cornea from the constant rubbing of blinking eyelids, thereby allowing it to heal. Likewise there are the toric lenses which are used to mask a small astigmatic correction. While there are a number of discount contact lenses available at stores, as well as online. Remember that before you can start using these lenses, check with your ophthalmologist or optometrist, to see which contact lens is best for your lifestyle. It is also imperative to have a yearly examination done before the initial use of contact lenses.