Types of contact lenses
There are two main types of contact lenses: soft and rigid.
Soft contact lenses are the most commonly prescribed type of contact lenses. Around 90% of all the contact lenses prescribed are soft lenses. Soft contact lenses are made from soft, flexible plastics, known as hydrogels, which contain water. The water allows oxygen to pass through the lens to the eye. This is important, as the cornea (the clear front surface of the eye) obtains its oxygen supply directly from the air.
Most soft contact lens wearers find that they adapt to the lenses quickly and they are comfortable straight away (unlike rigid lenses, which require some adaptation). This makes soft lenses suitable for people who do not want to wear their lenses every day, such as a footballer or netballer who only wears their lenses when they are playing.
Soft lenses are particularly suitable for sports, as they are difficult to accidentally dislodge. Soft lenses are suitable for correcting most refractive errors. Special “toric” lenses can be used to correct astigmatism. Soft lenses can be tinted to enhance or change the colour of the eyes.
Rigid lenses are made from plastics that are less flexible than those used for soft lenses. While the earliest materials used to make these lenses did not allow any oxygen to pass through the lens, the materials used today are permeable to oxygen, which is why these lenses are most commonly referred to as “rigid gas permeable” or “RGP” lenses. Some of the newer materials allow almost as much oxygen to reach the eye as if no lens was being worn.
Rigid lenses provide better vision than soft lenses, as the optics can be better controlled, and are suitable for a wider range of refractive errors. In some conditions in which the front surface of the eye becomes distorted, such as keratoconus, rigid lenses are the only way of satisfactorily correcting vision.
Rigid lenses require some adaptation on the part of the wearer. Typically they are less comfortable than soft lenses for the first week or two of wear, but after that they do not cause any discomfort. Adapting to rigid lenses is a bit like breaking in a new pair of shoes – initially they may be a little uncomfortable, but soon you can wear them all day without even noticing you have them on.
Rigid lenses are more durable than soft lenses, so they do not need to be replaced as often.