Dr. Teresa D Hrach OD
Contact Lenses, Contact Lens, eye examination
Just as 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:
Cornea measurements. An instrument called a keratometer will be used to measure the curvature of your eye's clear front surface (cornea).
The keratometer analyzes light reflections from your cornea and determines the curvature of your eye's surface. These measurements help your eye doctor choose 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 performed. Corneal topography provides extremely precise details about surface characteristics of the entire cornea.
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 analysis. A computer creates and prints out the resulting surface "map" of your eye, with different contours represented by varying colors.
Using a slit lamp
An eye doctor uses a biomicroscope to inspect the surface of an eye. This type of evaluation is needed before you are fitted with contact lenses. (Image: National Eye Institute)
Sometimes, corneal topography measurements are combined with wavefront measurements that can identify higher-order aberrations of the eye. These combined measurements can help your eye doctor determine the type of contact lenses that will give you the sharpest vision possible.
If your eye's surface is found to be somewhat irregular because of astigmatism, you may need 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 versi
, Contact Lenses
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