A contact lens is a thin lens placed directly on the surface of the eye and is a comfortable convenient alternative or addition to wearing glasses. Leonardo Da Vinci is frequently credited with introducing the idea of contact lenses in 1508, although his methods were not practical. Modern contact lenses have been in use for decades, and the technology is constantly changing and developing as manufacturers realise the need to improve the comfort, safety and vision needs of contact lens wearers. With these significant developments comes the assurance that there is a contact lens solution for each of the 150 million contact lens wearers worldwide.
Contact lenses are very versatile and are a good choice of vision correction for people who enjoy an active lifestyle, who want to look and feel more natural or who want a full field of vision wherever they look. There are a number of different options available for different vision conditions.
CONTACT LENSES FOR REFRACTIVE ERRORS
A refractive error occurs when the eye cannot accurately focus the light entering the eye, resulting in blurred vision. The most common refractive errors are myopia (shortsightedness), hyperopia (farsightedness), astigmatism and presbyopia, which is generally associated with aging.
For people who are shortsighted or farsighted there are numerous options, including hard or soft contact lenses. Most people choose to wear soft contact lenses which are generally more comfortable. There are a number of soft contact lenses to choose from. Daily wear contact lenses are worn on a daily basis and removed at night. Within this category are various disposable lenses which, as their name implies, are thrown away after use. The advantage of disposable lenses is convenience, no need for cleaning solutions, and a reduced risk of infection, but they can be expensive. Extended wear contact lenses can be worn while one is sleeping but need to be removed for cleaning at least once a week. They come with an increased chance of infection.
Gas-permeable lenses are the most common type of hard lenses. They are made of a stiff but permeable material which allows oxygen to connect with the surface of the eye. Due to their rigid nature, they may take time to adjust to, they need to be disinfected every day and should not be slept in. They are often preferred by people who have allergies or tend to get protein deposits on their soft contact lenses.
People with astigmatism have an unusual eye shape, and that shape can lead to blurred vision at all distances. Toric lenses are specifically designed for astigmatism. They differ from regular contact lenses in that they have different powers in different meridians and there is only one correct way to wear them. Rigid gas-permeable lenses are particularly helpful with astigmatism.
Traditional contact lenses are made to correct just one type of vision issue, but presbyopia, which is associated with aging, presents a different challenge. For example, a person may need a prescription for distance vision as well as one for close work. A simple solution could be to wear reading glasses over contact lenses for near vision, but some people prefer not to have the added inconvenience of glasses. There are contact lens options which deal effectively with both issues. Monovision involves the use of single-vision lenses to focus one eye for distance vision and the other for near vision. The brain then learns to see clearly at all distances. Multifocal contact lenses are comparable to glasses with bifocal or progressive lenses, in that they have prescriptions for both distance and near vision and are designed to provide a gradual transition between the two.
A scleral contact lens is a large firm contact lens that rests on the white of the eye, the sclera, rather than covering only a portion of the cornea. All modern scleral lenses are made with highly breathable, rigid gas permeable lens materials so that, although they cover the entire cornea, plenty of oxygen reaches the front surface of the eye to keep it healthy and comfortable. Scleral lenses may also be used to improve vision and reduce pain and light sensitivity for people suffering from disorders or injuries to the eye, such as severe dry eye syndrome, irregularly shaped corneas due to keratoconus, complications following eye surgery as well as discomfort wearing conventional contact lenses.
THERAPEUTIC SOFT LENSES
Soft lenses which do not have a prescription built into them are often used in the treatment and management of non-refractive conditions of the eye. A bandage contact lens allows the wearer to see while protecting an injured or diseased cornea from the constant rubbing of blinking eyelids. They may be used in the treatment of conditions including dry eyes, corneal abrasions and erosion, keratitis, corneal edema, chemical and burn injuries among others.
PHOTOCHROMIC CONTACT LENSES
Photochromic contact lenses are contact lenses that work in a similar fashion to photochromic glasses and are of particular benefit to people with light sensitivity. They appear clear indoors, gradually darkening when exposed to sunlight. While not intended to replace sunglasses, they do offer comfort to people who find bright light and glare disturbing, as well as providing some protection from harmful ultraviolet (UV) rays and the blue light from LED screens.
LENSES FOR COLOUR VISION DEFICIENCY
There is no cure for colour vision deficiency or colour blindness, as it is commonly known. However, some manufacturers claim that using special tinted glasses or wearing a red-tinted contact lens on one eye may increase some people's ability to compensate for missing colour filters in the eye and help them to differentiate between certain colours. Further evidence is however needed.
COLOURED CONTACT LENSES
Coloured contact lenses may be simply cosmetic to change the appearance of the eyes, or they may contain a prescription to correct a refractive error as well. Cosmetic lenses need to be treated like all contact lenses to avoid the risk of infection – they should be prescribed by an optometrist, cleaned regularly as directed by the optometrist, not be shared with others and definitely not bought at markets or party stores. Some coloured contact lenses completely cover the iris dramatically changing eye colour, while others merely tint the iris, highlighting the natural colour of the eyes.
CONTACT LENSES AND TECHNOLOGY
Contact lens technology is a fertile area of ongoing research with new developments emerging at a rapid rate. To provide medical professionals a means to monitor and manage their patients' health, some companies are working on contact lenses which will display information related to chronic medical conditions, such as glucose levels in diabetes and elevated eye pressure in glaucoma sufferers. Others are researching contact lenses which can deliver medication, for example eye drops that need to be inserted regularly or antihistamines to people with allergies. Telescopic lenses could help those with macular degeneration move between normal and magnified vision literally in the blink of an eye! A similar effect could be obtained with auto-focusing contact lenses.
Augmented reality is the ultimate demonstration of how technology can change our perception of the world. In the near future we could be experiencing augmented reality through our contact lenses, allowing us to display images, play videos and open web browsers right in our line of vision. We could be taking photographs just by blinking, creating maps in front of us as we walk, and seeing objects, once blurry in the foreground, come into focus. Science fiction or a likely reality?