Eye Matters
August 21, 2009
Contact Lens designs and intervals

Last week, we continued the discussion on contact lenses. We also grouped them according to a) what they’re made of b) their design c) how long they can be worn without removal and d) how often they should be disposed of.

Today we will discuss the disposal intervals of contact lenses. Even with the best care available, it is imperative to replace contact lenses frequently.{{more}} This helps to prevent contamination and the buildup of deposits (usually protein) on the lenses. Frequent replacement also helps reduce the risk of eye infections.

Depending on how frequently they should be discarded, soft contact lenses are classified as follows:

A) Daily disposables (to be discarded every single day)

B) Bi-weekly disposables (to be discarded after two weeks -usually used for daytime wear)

C) Weekly disposables (to be discarded after one week -usually used for overnight wear)

D) Continuous wear (to be discarded every four weeks -usually used for 30 day wear)

E) Planned replacement lenses (to be discarded every few months decided by the eye doctor)

Gas permeable contact lenses do not need to be discarded as frequently as soft contact lenses. This is because they are more resistant to protein buildup and other lens deposits. They can be used for a year or longer before they need replacement.

Now let’s talk about contact lens designs. There are many designs available for the correction of various types of vision challenges.

Spherical contact lenses are typically the rounded designs that correct nearsightedness (myopia) and farsightedness (hyperopia).

Toric contact lenses correct astigmatism as well as myopia or hyperopia. They are created at different angles. One for myopia or hyperopia and the other for astigmatism

Bifocal or Progressive contact lenses are lenses that have different zones for distance and near. These are used for most people over the age of 40 who are also in need of reading glasses.

There are also custom lenses that are made for hard to fit eyes. They are less common and are only used for special situations such as correcting irregular shaped corneas. A condition known as keratoconus.

Before we wrap up this week’s discussion, I would like to answer a question that was sent to me by e-mail.

Question: Can a contact lens get lost behind my eye?

Answer: The answer is no. There is a thin membrane that covers your eye and is connected to the inside of your eyelids, making it physically impossible for the contact lenses to get lost. The contact lens may slide into the uppermost corner of your eye, but they do not get lost. They just need to be coaxed back down.

That’s all for this week folks. Next week we will discuss other contact lens features such as coloured contact lenses, special effect lenses, prosthetic lenses, UV inhibiting lenses and hybrid lenses.

Dr Kenneth Onu is a resident Consultant Ophthalmologist at the Beachmont Eye Institute/Eyes R Us. Send questions to: Beachmont@gmail.com

Tel: 784 456-1210