A few examples of Contact lenses are:
The shortest replacement schedule is single use (daily disposable) lenses, which are disposed of each night. These may be best for patients with ocular allergies or other conditions, because it limits deposits of antigens and protein. Single use lenses are also useful for people who use contacts infrequently, or for purposes (e.g. swimming or other sporting activities) where losing a lens is likely.
Two-week Replacement Disposables
The main advantage of wearing disposable lenses is that you put a fresh pair of lenses in your eyes every two weeks. Another advantage is ease of care with multipurpose solutions.
One-month Replacement Disposables
Similar to two-week replacement lenses but you throw them out every 30 days.
Conventional Contact Lenses
These are the original soft contact lenses. It is recommended these lenses be replaced on a yearly basis. Conventional lenses are more care intensive than disposable lenses.
Color Contact Lenses
Certain soft contact lenses come in colors to either enhance your eye color or completely change it.
Toric for Astigmatism
Toric lenses are made from the same materials as regular contact lenses but have a few extra characteristics:
• They correct for both spherical and cylindrical aberration.
• They may have a specific 'top' and 'bottom', as they are not symmetrical around their center and must not be rotated. Lenses must be designed to maintain their orientation regardless of eye movement. Often lenses are thicker at the bottom and this thicker zone is pushed down by the upper eyelid during blinking to allow the lens to rotate into the correct position (with this thicker zone at the 6 o'clock position on the eye). Toric lenses are usually marked with tiny striations to assist their fitting.
• They are usually more expensive to produce than non-toric lenses
Bifocal Contact Lenses
Multifocal soft contact lenses are more complex to manufacture and require more skill to fit. All soft bifocal contact lenses are considered "simultaneous vision" because both far and near vision corrections are presented simultaneously to the retina, regardless of the position of the eye. Of course, only one correction is correct, the incorrect correction causes blur. Commonly these are designed with distance correction in the center of the lens and near correction in the periphery, or vice versa.
These lenses were the original contact lenses made several decades ago from a plastic called PMMA. For a long time they were the only kind of lens but they are seldom used anymore as they have several drawbacks and have been superseded by “rigid” lenses. Rigid, or gas permeable, lenses are similar to hard lenses in design and appearance, however as the name suggests, the material they are made of is permeable to gases.
Soft lenses are slightly larger and more flexible than rigid or hard lenses. Soft lenses are made of materials which soak up water, and it is this uptake of water that allows oxygen to transfer to the cornea. Soft lens material itself is impermeable, so the oxygen is transmitted via the water.