How Often Should You Get Contact Lens Eye Measurement?

About 36 million people in America wear contact lenses, with 80 percent of them wearing soft lenses daily. Contact lens eye exams including measurements are recommended once a year. At the most, you shouldn't go longer than two years between measurements. People with diabetes, a family history of eye diseases or poor health may need to have their eyes looked at more often. Eye exams for contact lenses are different than those for eyeglasses and use different tests for proper lens fitting.

Curvature and Size Measurement

• Contact lens measurements are usually taken annually. They are necessary because one lens doesn't fit everyone. For instance, the curvature of the eye may be too steep or flat. Eye doctors measure the eye surface and curvature with an instrument called a keratometer. The keratometer determines how curved the eye surface is and analyzes light reflections from your cornea. The measurement is used to determine the curve and size of the contact lens. A corneal topography may also be done to analyze the manner in which light projected into the eye travels. This will provide very specific details about the eye's surface characteristics. The corneal topographer projects light beams into the eye. A surface map of the eye is then produced by computer, showing the different contours and measurements of the eye.

Pupil Measurement

• The doctor may use a ruler or card to measure the pupil. These have different pupil sizes on them and are held next to your eye to figure out which is the best match to your eye measurement. There are also automated instruments to measure pupil size. They are much more precise and can also measure the vertical and horizontal diameters of the pupils.

Tear Production

• Contact lens fittings may also include an evaluation of tear production. The doctor will insert a small piece of paper beneath the lower eyelid. The eyes are kept closed for five minutes, then the doctor removes the paper. If you have dry eyes, there won't be much moisture on the strip. Instead of using this method, the doctor may apply eye drops or a paper strip containing fluorescein dye to the tear layer on your eye to evaluate how long it takes for your tears to evaporate. If your eyes are too dry or you don't make an adequate amount of tears, contact lenses may not be the solution for you. You may also be prescribed contact lenses with silicone hydrogel material which are better for dry eyes.

Lens Fit

• The health of your cornea is also an important factor in contact lens measurement exams. After you are fitted with contact lenses, you'll be given a trial pair. You must go for a second visit to evaluate whether the measurement and prescription are correct. A biomicroscope will magnify the cornea and tissues to show the eye doctor changes that may be caused by wearing contact lenses. The instrument is also used to determine whether a trial pair of contact lenses fit correctly by evaluating the movement and alignment of the lens on the eye surface. This instrument will also be used at annual contact lens appointments.