Eye Exams for Contact Lenses

If you already wear or are interested in contact lenses, make sure you say so when you schedule your appointment for an eye exam. You'll need some extra time and additional tests such as an evaluation of your eye's surface (cornea) so that your eye doctor can make sure you receive a proper contact lens fitting.

You'll first undergo a routine eye exam in which your eye doctor will use a bright light to view and assess the structure of the outside of your eye. Your eye doctor also will observe how well your eye muscles function. A standard visual acuity test will be given to determine your ability to see letters or numbers on an eye chart. If you do require vision correction, then the eye doctor will determine the corrective lens prescription that will give you the best vision. [See also: What To Expect From a Comprehensive Eye Exam.]

Now that the standard eye exam has been completed, your eye doctor will need additional information before you can be fitted for contact lenses. You may be asked general questions about your lifestyle and preferences regarding contact lenses, such as whether you might want to change your eye color with color contact lenses or if you're interested in options such as daily disposables or overnight wear. Your eye doctor may also discuss the option of rigid gas permeable (RGP or GP) contact lenses, although most people today are fitted with soft lenses.

Your eye doctor may question you about how you might want to correct vision problems related to aging. At about age 40 or maybe older, you will develop a condition known as presbyopia that decreases your ability to see clearly at all distances. To correct presbyopia, your eye doctor may offer you the choice of multifocal or bifocal contact lenses or monovision, in which one contact lens corrects for near vision and the other contact lens corrects for distance vision.

Just like one shoe size doesn't fit all, one contact lens size doesn't fit all. If the curvature of a contact lens is too flat or too steep for your eye's shape, you could experience discomfort or even eye damage. Other aspects of a contact lens fitting include:

• Measurement of your eye's surface and curvature: An instrument called a keratometer, which is a type of digital camera, will be used to measure the curvature of your eye's clear front surface (cornea). With one version of the instrument, you sit and face the instrument. You then place your chin on a brace so that your head is held still while the instrument photographs your eye. The keratometer automatically assesses images of your cornea and creates mathematical representations of the curvature of your eye's surface (K-readings). These measurements help your eye doctor determine the proper curve and size for your contact lenses.
   
  Because the keratometer measures only a small, limited section of the cornea, additional computerized measurements of your cornea (corneal topography) may be done. Corneal topography provides extremely precise details about surface characteristics of the cornea by analyzing photographic images taken of the way light projected into your eye travels. With one version of a corneal topographer, you are seated with your forehead resting against a curved brace. Circular patterns of light then are beamed into your eye for photographic analysis. A computer creates and prints out the resulting surface "map" of your eye, with different contours represented by varying colors. [See also: Refraction: How the Eye Sees.]
   
  If your eye's surface is found to be somewhat irregular because of astigmatism, you may require a special design of lens known as a toric contact lens that is shaped to offset distortions of your eye to provide sharper vision. At one time, only rigid contact lenses could correct for astigmatism. But there are now many brands of soft toric lenses. Toric lenses also are available in disposable, multifocal, extended wear, and colored versions.
   

• Pupil and Iris Measurements: Other measurements will be taken with a pupil card, ruler, or pupillometer to determine your eye's pupil size. In a simple approach, a card or ruler showing different pupil sizes will be held next to your eye to determine the best match. Some automated systems of measuring the diameter of your pupil, sometimes both horizontally and vertically, involve placing a small, magnified screen in front of your eye sometimes with a hand-held instrument. The magnified image of your eye then is automatically converted to an accurate pupil measurement. Similar technologies also may be used to measure the diameter of the colored portion of your eye (iris). Pupil and iris measurements help achieve a proper sizing and orientation of your contact lens.
   

• Tear film evaluation: Contact lens fittings may also include a tear film evaluation. Your eye's moisture content may be evaluated through use of small strip of paper inserted underneath the lower eyelid. You close your eyes for about five minutes, and then the paper is removed to determine how much moisture your eye produced. Another method of detecting dry eye involves placing fluorescein dye in your eye through eye drops, and then evaluating how long it takes for the dye to be washed away by your eye's tears. If your eyes don't produce enough moisture and you have severe dry eye, contact lenses may not be right for you. Additionally, certain contact lenses such as those made of silicone hydrogel material may work better for eyes that are dry.
   
• Evaluation of your eye's surface and contact lens fit: The health of your cornea will also be evaluated using a biomicroscope. This lighted instrument with magnification will provide detailed information about your eye's surface as a baseline for your doctor to evaluate any future changes to your eyes related to contact lens wear. The biomicroscope can also be used to evaluate the fit of a trial pair of lenses, because it allows the doctor to observe alignment of the lens as it rests on the surface of your eye.
   
  Evaluating how the trial lens moves after each blink also helps your eye doctor see how much the lens moves with each blink to make sure that the fit is correct. As an example, your eye doctor will make sure that the edge of the lens following a blink does not angle away or make too much contact with the eye. You'll typically need to wear these trial lenses at least 15 minutes so that initial tearing of the eye stops and stabilizes, which helps in making a proper evaluation of how the lens fits your eye without the presence of excess moisture caused by tearing.
   
  In follow-up visits, your eye doctor may use a special dye (fluorescein staining) to place on your eye to check for defects and make sure your contact lenses are not damaging your eye's surface. You will need to remove your contact lenses before this test is performed.

After finding a contact lens that fits properly, is comfortable for you, and provides good vision, your eye doctor will write a contact lens prescription. This prescription will designate contact lens power, a shape matching the curvature of your eye (base curve), and diameter.

It typically takes about two office visits to complete the contact lens fitting. After that, your eyes will need to be examined once annually so that your eye doctor can monitor the health of your eyes. A few patients may need contact lens progress evaluations prior to the annual visit.

Once you are successfully fitted for contact lenses, keep in mind that you still will need extra evaluation to assess eye health. This means that even a routine contact lens eye exam typically costs more than a regular eye exam.