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Before soft contact lenses were introduced, hard contact lenses made of PMMA, or polymethyl methacrylate, were used. They did not allow for oxygen transfer to the cornea and often caused the cornea to swell. For this reason, hard contact lenses are considered obsolete and are rarely used in the modern day.
Soft contact lenses are the most common type and account for over 85% of contact lenses dispensed. Traditional soft contact lenses are made of soft plastic polymers and water. They allow oxygen to permeate through the lens material to the cornea and are generally very comfortable.
The advantages of soft contacts are that they are almost instantly comfortable and come in many different prescriptions and designs. The potential disadvantage is that (for some prescriptions) they do not offer the same visual acuity as gas permeable lenses.
Your eye care professional, like the high-quality eye doctors at McDonald Optical in Iowa City, can help you determine which design will be best for your prescription.
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Some advantages of disposable contacts include:
- They are soft lenses designed to be discarded daily, weekly, bi-weekly, or monthly.
- By replacing lenses regularly, long-term protein deposits (which can affect vision, comfort, and the eyes’ health) do not build up.
- Disposable contacts are convenient and require less maintenance than traditional soft lenses.
- Disposable lenses are also available in most prescriptions.
As a point of precaution, those who wear disposable contacts should be aware that the contacts must be replaced at their designated time to avoid eye infection.
Extended wear contact lenses are gas-permeable or soft lenses worn continuously for up to 30 days.
While extended wear lenses offer the convenience of not taking them out at night, sleeping in contact lenses results in a higher risk of developing infections, corneal ulcers, and abnormal blood vessel growth in the cornea. Therefore, more frequent follow-up is required, and some doctors will not recommend extended wear lenses.
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Gas Permeable Lenses
Rigid Gas Permeable (RGP) or just Gas Permeable (GP) lenses are sometimes mistaken for old-fashioned hard contact lenses. In truth, they’re actually more pliable, more comfortable, and most importantly, allow oxygen to the cornea.
Gas-perm lenses transmit more oxygen to the cornea than traditional soft contact lenses do, and because gas permeable lenses are rigid, they do not change their shape when you blink and can offer sharper vision than soft contacts. This means they’re much more durable than soft lenses, and because they do not contain water, proteins and lipids do not adhere to them as quickly as with soft lenses. As a bonus, GP lenses also come in numerous bi-focal and multi-focal designs.
GP lenses are much more durable than soft lenses, and because they do not contain water, proteins and lipids do not adhere to them as quickly as with soft lenses. They also come in numerous bi-focal and multi-focal designs.
Unfortunately, the most significant disadvantage to GP lenses is that they are not immediately comfortable like with soft lenses. In general, they take 3 to 4 days to adapt to, and they need to be worn regularly (although not every day) to achieve maximum comfort. Also, they can dislodge from the eye more easily than soft lenses because they are smaller in size.
Toric Contact lenses
Toric contact lenses are designed to correct for astigmatism. They are available in both soft and gas-permeable designs.
These lenses have one power vertically and another horizontally and are weighted at the bottom, allowing the lenses to center correctly on the eye. Toric lenses are more difficult to fit and generally require more time from the patient and eye doctor for fitting and adaptation.
Bifocal Contact lenses
Bifocal contact lenses, similar to bifocal glasses, have more than one power to allow an individual to have a clear vision, near and far. They are available in both soft lens and gas permeable lens designs.
Another alternative to bifocal contacts is monovision correction. With these lenses, one eye is used for distance and the other eye for near or reading vision. Both of these lens types require more time from the eye doctor for fitting. They also need more time for the patient to adapt to their differences.
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