Types of contact lenses
Developments in materials and designs of contact lenses are constantly changing as newer technology improves on previous contact lenses. Recent developments include toric (astigmatism-correcting) lenses which are replaced on a daily basis and the development of lenses which allow enough oxygen to pass through the lens that they can be worn on an overnight basis.
Disposable contact lenses
Disposable contact lenses are lenses which are designed to be replaced on a regular basis , usually either daily, two-weekly or monthly. The more often a lens is replaced, the less the lens will become deposited with proteins and oils. Many of the problems that contact lens wearers experienced when contact lenses were replaced on an annual or two yearly basis are seldom seen nowadays. Disposable contact lenses are therefore a healthier alternative . Daily disposable contact lenses are a great option for people who only want to wear their contact lenses a few times per week, for example, for sports. They also remove the need for cleaning, since they are inserted in the morning (or before you play sports) and then thrown away afterward, offering exceptional convenience and good value for the money. Lenses which are replaced two-weekly or monthly are a good value if you want to wear lenses every day. They work out to be cheaper than daily disposable over the period of two to four weeks, although you will need to clean them nightly.
Leave-in (extended wear) contact lenses
Leave-in (extended wear) contact lenses are designed to be worn continuously for 30 days and nights and then replaced with a new contact lens. They offer the ultimate in convenience , since they usually don't need removing or mechanically cleaning. Other advantages include being able to see without struggling to find your glasses if you get up in the night, or not having to worry about removing lenses with dirty hands if you go camping. You also won't need to remember to carry bottles of solutions around with you if you go out with friends and end up staying out the night!
Gas permeable contact lenses
Gas permeable contact lenses are usually used for the correction of moderate levels of astigmatism. They provide excellent clarity of vision , especially in cases where the astigmatism is irregular (such as with keratoconus). They require a longer period of adaptation than soft lenses.Gas permeable contact lenses offer excellent long-term corneal health since they allow almost as much oxygen to pass through to the cornea as without a lens on the eye. Many of the problems associated with the reduced oxygen flow through the old-style "hard lenses" are seldom seen nowadays due to the developments in these modern gas permeable materials.
Myopia (short-sightedness or near-sightedness) is a condition in which the eyeball itself is either too long, or the front of the eye (the cornea) is too curved, or a combination of both. The result is that light from distant objects is focused in front of the retina (instead of on the retina). This makes doing things like driving and reading far-off signs difficult. Myopia can be corrected with either soft (disposable) contact lenses or RGP (gas permeable) contact lenses.
Hyperopia (long-sightedness or far-sightedness) is a condition in which the eyeball is too short, or the cornea is too curved, or a combination of both. The result is that light from objects is focused behind the retina. We can use some of the focusing power of the natural lens within the eye to help refocus the light, but this can lead to "eyestrain" or tired eyes, especially when working at near. The focusing ability of the eyes also reduces as we get older, making it more difficult to overcome the focusing problem. Hyperopia can be corrected with either soft (disposable) contact lenses or RGP (gas permeable) contact lenses.
Presbyopia is the loss of focusing ability of the eyes. The focusing lens inside the eye hardens as we get older, resulting in the closest point that we can focus on moving further and further back until reading small print becomes more and more difficult. This is why many people who have never worn spectacles find that they need a pair of reading spectacles when they reach their mid-forties. There are a number of contact lens designs available now which offer an alternative to glasses if you are having problems with your reading vision due to presbyopia.
Astigmatism is a condition in which the front of the eye (the cornea) is oval shaped instead of round. Some people describe it as having rugby ball shaped cornea instead of a soccer ball shaped cornea. There are two types of astigmatism, regular and irregular. Regular astigmatism is able to be corrected with glasses, soft (toric) and RGP (gas permeable) contact lenses.
The range of contact lenses available to correct regular astigmatism is constantly increasing. Many people with astigmatism have been told in the past that their eyes aren't suitable for contact lenses, due to limited designs available at the time. You should consult your eye-care practitioner to find out if you may be able to be fitted now with the increased ranges of contact lenses.
Irregular astigmatism is usually not well corrected with spectacles or soft contact lenses, unless it is fairly mild. It can be caused by conditions such as keratoconus and corneal scarring. RGP (gas permeable) contact lenses correct the vision by maintaining their shape on the cornea, with any corneal irregularity being filled by the tears behind the lens. Soft contact lenses, when tried with irregular astigmatism, tend to mold to the shape of the eye, thus transferring the distortion.
Keratoconus is a condition where the cornea thins and then slowly pushes forward in a cone shape. If an eye with astigmatism is described as a rugby ball lying on it's side, think of a cornea with keratoconus as a rugby ball with the pointed end facing forward. Early cases will often still see well with spectacles or soft contact lenses, but as the condition progresses, RGP (gas permeable) lenses are needed to better correct the distortion in vision.
Many new designs of gas permeable lenses are available for the correction of keratoconus, including large diameter contact lenses which can offer better centration and comfort than traditional lenses.
Dry Eyes and contact lenses
Many newer contact lens materials are available nowadays which offer better comfort to people with dry eyes than previous lens materials. Specially designed polymers have been developed which dry out less on the eye, resulting in less lens awareness, better clarity of vision and less reliance on rewetting drops. See your eye care practitioner to find out if you are suitable for one of the newer material type of contact lenses.