Contact Lenses 101

Contact Lenses 101: An overview

Medical Contact Lens vs. Elective (Cosmetic) Contacts

Contact lenses are considered medically necessary if a patient can see well only with contact lenses, and not with glasses. Usually, this is due to an irregular front surface of the eye (cornea) that causes the incoming light to be scattered rather than focused on the back of the eye (retina). Some of the more common causes of this are corneal trauma, post surgical corneal irregularity and keratoconus. Keratoconus is a condition that causes a progressive steepening and deformation of the corneal surface. The cornea becomes thin and "cone shaped" and in some cases requires surgery if contact lens wear is not successful.

In all these cases, the contact lens creates a smooth surface on the front of the eye that allows light to be focused on the retina. Usually rigid gas permeable lenses are prescribed to correct corneal surface irregularities. If you cannot tolerate these lenses customized soft lenses or a combination of soft and rigid lenses are used.

If you suspect you might have such a condition, you need an eye exam to diagnose which condition you have. You may arrange an eye exam at Casey Eye Institute, or with your regular eye doctor. If you see fine with glasses but would like to wear contact lenses for any reason (better side vision, no raindrops on your glasses, better for sports), it is called an elective or cosmetic contact lens fit. We do both types of contact lens fittings at the Casey Eye Institute.

Some insurance companies will provide benefits for medical contact lens fittings. Coverage varies from one carrier to another. We encourage you to check your coverage with your insurance company prior to contact lens fitting.

Daily Wear vs. Extended Wear

Many people want the convenience of putting their lenses in and leaving them in for a week at a time, sleeping with the lenses on. This is called extended wear, and is very convenient. However, it is less healthy for the eyes. "Daily wear" lenses are removed each evening for cleaning and disinfecting, and are more healthful for most patients. Sleeping in contact lenses can cause many problems, including greatly increasing the risk of eye infections. 

Eye infections are serious, and if an ulcer forms on the cornea, your eye health and vision maybe permanently compromised. Sleeping in contact lenses can cause edema, which is swelling, and if the cornea (the front of the eye) is swollen, it becomes cloudy and you can't see through it very well. So, please, don’t sleep in your contact lenses unless specifically prescribed lenses by your eye doctor.

RGPs vs. Soft

There are two main types of contact lenses, soft lenses (hydrogel or hydrophilic) and rigid gas permeable (GP) lenses. Soft lenses are very flexible, and are generally larger in diameter than RGPs. Soft lenses are generally very comfortable right from the start, but some prescriptions may not provide vision as crisp as RGPs. Soft lenses are preferably disposable (see section on disposables vs. conventionals), as it is healthier to change the lenses regularly. RGPs are stiffer (they are the improved 'hard' lenses), and usually smaller. They are comfortable after you become adapted to them, and may give crisper vision for certain prescriptions. A pair of RGPs generally are used for at least a year. Both soft and rigid contact lenses are good. Your prescription will determine which type of lens will give you the best combination of comfort and clarity.

Disposable, Planned Replacement and Conventional Lenses

These terms are used for soft lenses. We use the word "conventional" when referring to a soft lens that is used for an entire year. These are generally used for very high prescriptions that require custom-made lenses. "Disposables" are lenses that are discarded after one use, two weeks, or every month, depending on the lens design and prescribed replacement schedule. before being discarded. Planned replacement lenses are tossed on a schedule, ranging from monthly to every six months, depending on the lens and the condition of the eyes. 

The advantage of replacing the lens more often is that it's better for your eye health to have a fresh clean lens periodically. The more often the lens is replaced, the better. You discard the lens before protein, mucas and other environmental contaminants have a chance to build up, and before the lens has time to deteriorate. One-day lenses are preferable, as you don't need to clean them at all, and you have a fresh, sterile lens each day. The one-day lenses also eliminate reactions to cleaning or other allergies, since you don't have to use or buy solutions. However, not all prescriptions come in one-day lenses.

Since the disposable and planned replacement lenses were developed, there are many fewer complications from contact lens wear.

RGPs (rigid gas permeable lenses) are worn for at least a year, but we consider them separately from the soft lenses and don't call them "conventionals." The material they are made from does not deteriorate in the way soft contact lens materials can, so RGPs can be healthful to wear for longer than a year.

Special Uses of Contact Lenses

Contact lenses have many uses in addition to replacing glasses. If your glasses are very thick, or if you have a very complicated prescription, contact lenses may be used with thinner glasses to give you better vision than with glasses or contact lenses alone. The glasses can be a bifocal if needed, and will be thinner and lighter weight than they would be without the contact lenses.

If one eye has a prescription much different than the other eye (anisometropia) so that the glasses lens is much thicker over one eye, you can wear a contact lens can be used in only one eye. Then both glasses lenses can be equal and thinner. Also, many people with this type of prescription wear contacts only, without glasses.

Bifocal Contact Lenses

Presbyopia is a condition in which the eyes won't focus up close the way they used to. Presbyopia affects everyone. It is a normal, aspect of aging, and usually starts sometime after age forty. There are several contact lens options to help with presbyopic eyes.

We can prescribe contact lenses to give the best distance vision with each eye, in conjunction with reading glasses. This works best for people who must have the best distance and/or near vision possible, or those who don't mind reaching for reading glasses.

The other options for helping near vision in presbyopes with contact lenses compromise clear vision somewhat, so you must be motivated to accept slightly blurred vision at distance and at near which could allow more freedom from glasses. Both of the next two options can be done in either soft or rigid contact lenses.

Bifocal contact lenses are available. They offer less clarity of vision than bifocal glasses, but they do allow both of the eyes to see at distance and up close, decreasing the need for reading glasses.

Monovision is where we set one eye for distance vision and the other eye for near vision. It takes the brain a few weeks to adjust but, as with bifocal contact lens wear, works quite well after you adapt. Driving at night can be more difficult with monovision.


It used to be that people with astigmatism couldn't wear contacts, or could only wear rigid gas permeable (RGP) contacts. New technology has allowed the development of soft "toric" lenses (that's what we call lenses for astigmatism) for almost any prescription. These lenses may be fit over several visits. The vision is generally very good with toric lenses, but might not be as crisp as with glasses, especially for people with a high amount of astigmatism. Depending on your prescription, eye health, and vision needs, we may recommend either soft or RGP lenses.

Colored Contact Lenses

There are several brands of colored contact lenses now available. The one-day and two-week disposables are favorites with most patients. There are colored lenses that add just a little extra color to blue and green eyes, and there are lenses that completely change the eye color for eyes of any color. There are also fancy, scary lenses for Halloween.

Brands of Contact Lenses

There are many different brands and types of contact lenses. The lens best for you depends on your visual and eye health needs. After we've analyzed the data from your eye exam, we determine which lenses may work best for you. If there are several options, we will involve you in the decision making process. Our goal is to prescribe you into the type of lenses which will be the most comfortable and healthy for your eyes, and give you the clearest, functional vision.

Reading a Contact Lens Prescription

The prescription for contact lenses includes more information than the prescription for eyeglasses. Special measurements will need to be taken of the curvature of the eye. In addition, the physician will determine if the eyes are too dry for contact lenses, and if there are any corneal problems that may prevent a person from wearing contact lenses. Trial lenses are usually tested on the eyes for a period of time to ensure proper fit.

The contact lens prescription should  includes the following:

  • Specific name (like the make and model) of the contact lens
  • Contact lens power (measured in diopters, like eyeglasses)
  • Contact lens base curve
  • Diameter of the lens