Contact Lenses: an introduction

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Simply put, contact lenses are thin, transparent, plastic discs resting on the cornea of your eye. The way they work is of course a tad more complicated. Contact lenses correct so called refractive errors such as myopia, or nearsightedness, and hyperopia, also known as farsightedness.

For people who don’t need contact lenses, light enters the cornea and is focused perfectly in one single point on the retina. The light converts into signals that are developed into images in the brain. Refractive errors occur when the eye is unable to focus light onto the retina this way, and can lead to blurry vision. Myopia, for example, usually happens when the eyeball is too long and light from distant objects gets focused in front of the retina instead of on it. Close objects will look fine, while distant objects will appear blurry. In this case, a concave contact lens will divert the light so that it comes out correctly on the retina.

The type of refractive error will decide the shape of the contact lens needed. In technical terms, the strength of the contact lens will be expressed in dioptres, which is a measurement of how much the lens bends light. A layer of tear fluid on the surface of your eye, together with the pressure of your eyelid, will keep the contact lens in place, and each blink of the eye lubricates the cornea and ensures that no impurities can stick to the contact lens.

Many people prefer contact lenses to eyeglasses as they are much closer to natural sight. This is partly because contact lenses correct the refractive error closer to the eye and follow its movement, while also providing a natural field of vision.

The first ever contact lenses were made of the same hard plastic that is used to make Plexiglas. Hard contact lenses caused wearers a lot of discomfort since they didn’t allow oxygen to pass through to the cornea, which is a necessity for basic eye health. Soft contact lenses are generally much more comfortable and quicker to get used to, largely because they are hydrophilic, which means that they absorb water and hence are oxygen permeable. This also allows the wearer to keep their contact lenses in for a longer time. In America, according to the Food and Drug Administration, 82% of contact lens wearers use soft contact lenses.

The middle ground between hard and soft lenses is the rigid, gas-permeable contact lens from the 1970s, which combines the benefits of PMMA (from the early, hard contact lenses), silicone, and a type of plastic called fluoropolymers. This makes it more durable than soft contact lenses while still letting oxygen through to the cornea and providing crisp vision for a long time.

Contact lenses are available for daily wear, being removed each night before going to bed, or extended wear, in which case they can be worn for up to a week without removing them. There are contact lenses that change your eye colour and those that protect your eyes from UV-radiation. A recent, popular addition to the contact lens family is the daily disposable, which like the name suggests is a daily lens that is thrown away at the end of each day. One reason for its popularity is the convenience of not having to care for your contact lenses, compared to bi-weekly and monthly contact lenses which require a lot of cleaning and disinfecting. Less common are the corneal reshaping contact lenses which are worn overnight to reshape the cornea so that your vision will be temporarily fine the following day.

People with certain eye conditions are less suitable for contact lens wear. If you are diabetic or have a history of corneal infections, your Optician is likely not to recommend you to wear contacts, and the same goes for people who are regularly exposed to chemical fumes or dust. In the past, sufferers of dry eye syndrome were very rarely prescribed contact lenses since these would dry up their eyes way too quickly, but with recent technology things are changing, and certain brands are in fact specifically designed to meet the demands of contact lens wearers with dry eye syndrome.

In cases of much distorted corneas, like in some people suffering from keratoconus, a very different approach to contact lens wear may be required. With the so called piggybacking technique the wearer would need two contact lenses for each eye, a rigid gas-permeable contact lens sitting on top of a soft lens to keep it in place. In people with papillary conjunctivitis, however, the eyes secrete proteins. This makes soft contact lens wear impossible, as the deposits would build up on the lens and make them cloudy. Daily disposable contact lenses are often recommended, as there isn’t enough time for the proteins to build up in one day, and sometimes rigid gas-permeables can work since proteins don’t generally stick to them.

If you want to try your luck with contact lenses, you need to visit your Optician to get a prescription. Contact lenses are classified as medical devices, and it is UK law that contact lens suppliers are not allowed to sell contact lenses to people who don’t have a valid prescription. Once your Optician has examined your eyes and given you a contact lens prescription, it is entirely up to you whether you want to order your lenses straight from them or from an online supplier. Many former eyeglass wearers swear by their contacts and say that they could never go back – hopefully you’ll be one of them.

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