One size does not fit all when it comes to contact lenses. Your eye doctor will need to take some measurements to properly fit your contact lenses. Contact lenses that do not fit properly could cause discomfort, blurry vision or even damage the eye. Here are some of the measurements your eye doctor will take for a contact lens fitting:
In order to assure that the fitting curve of the lens properly fits the curve of your eye, your doctor will measure the curvature of the cornea or front surface of the eye. The curvature is measured with an instrument called a keratometer to determine the appropriate curve for your contact lenses. If you have astigmatism, the curvature of your cornea is not perfectly round and therefore a “toric” lens, which is designed specifically for an eye with astigmatism, would be fit to provide the best vision and lens fit. In certain cases your eye doctor may decide to measure your cornea in greater detail with a mapping of the corneal surface called corneal topography.
Pupil or Iris Size
Your eye doctor may measure the size of your pupil or your iris (the colored area of your eye) with an instrument called a biomicroscope or slit lamp or manually with a ruler or card. This measurement is especially important if you are considering specialized lenses such as Gas Permeable (GP) contacts.
Tear Film Evaluation
One of the most common problems affecting contact lens wear is dry eyes. If the lenses are not kept adequately hydrated and moist, they will become uncomfortable and your eyes will feel dry, irritated and itchy. Particularly if you have dry eye syndrome, your doctor will want to make sure that you have a sufficient tear film to keep the lenses moist and comfortable, otherwise, contact lenses may not be a suitable vision option.
A tear film evaluation is performed by the doctor by putting a drop of liquid dye on your eye and then viewing your tears with a slit lamp or by placing a special strip of paper under the lid to absorb the tears to see how much moisture is produced. If your tear film is weak, your eye doctor may recommend certain types of contact lenses that are more successful in maintaining moisture.
Contact Lens Trial and Prescription
After deciding which pair of lenses could work best with your eyes, the eye doctor may have you try on a pair of lenses to confirm the fit and comfort before finalizing and ordering your lenses. The doctor or assistant would insert the lenses and keep them in for 15-20 minutes before the doctor exams the fit, movement and tearing in your eye. If after the fitting, the lenses appear to be a good fit, your eye doctor will order the lenses for you. Your eye doctor will also provide care and hygiene instructions including how to insert and remove your lenses, how long to wear them and how to store them if relevant.
Your eye doctor may request that you schedule a follow-up appointment to check that your contact lenses are fitting properly and that your eyes are adjusting properly. If you are experiencing discomfort or dryness in your eyes you should visit your eye doctor as soon as possible. Your eye doctor may decide to try a different lens, a different contact lens disinfecting solution or to try an adjustment in your wearing schedule.