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Lens Types
Single Vision Lenses
Single vision lenses have the same optical power throughout the lens. Depending on the patient's eyeglass prescriptions these lenses may be appropriate for full or part-time use at distance only, near only, or both distance and near.
When a patient develops presbyopia they need a different optical power to see clearly at distance and near. Depending on the distance they are conducting their near visual tasks, different optical powers may be needed (e.g., one pair of eyeglasses may be needed to read a book, and another pair may be needed to see the computer or desktop which is at a farther distance). Although this can be accomplished with different single vision eyeglasses (e.g., one pair for driving, one pair for computer, and one pair for reading), most patients will find that a multifocal lens (bifocal, trifocal, or progressive) is more functional, convenient, and desirable.
Bifocals
Bifocal lenses have two different optical powers within the same lens. Usually one optical power is for distance and the other is for a specified near distance. The near section is located in the lower part of the lens so that near materials must be held in your inferior direction of gaze to see them clearly.
Trifocals
Trifocal lenses have three different optical powers within the same lens. Usually one optical power is for distance, one is for near, and the other is for intermediate (in-between distances).
Progressives (invisible or no-line multifocals)
Modern technology has allowed the development of ever-more advanced progressive lenses with easier adaptation. They are designed to be the most similar to "natural" vision possible. In a progressive lens, the distance power is located in the top part of the lens and the near section is located in the lower part of the lens. One of the main functional advantages of this type of lens is that there is also a "progression" of optical power throughout the lens from the distance section to the near section which can be used for various intermediate (in-between distance) visual tasks. Improved cosmetic appearance is a definite advantage since no lines are visible; it is for this reason they are also called invisible or no-line multifocals. Because there is some adaptation and there are some limitations with the use of these lenses, proper fitting, adjustment, and instruction on their proper use is particularly important.
Other Specialty Multifocal Occupational Lenses
If you were to look at a near object located above your head with normal multifocal lenses it would appear blurry since no near add would be present. Single vision eyeglasses for near can be used to accomplish these tasks, however, they cannot be worn continuously since they cause blurry vision at distance. Occupational bifocals and trifocals are available for this specialized task (Please ask our optometrist or staff for more information).
Computer Lenses for Presbyopia
Ophthalmic companies have developed task-specific lenses which have been designed for computer/reading use only. These lenses are similar to a progressive lens with the near section located in the lower part of the lens, but the top part of the lens contains an intermediate distance optical power for computer use (these lenses are blurry for distant objects). Although for most of our patients progressives lenses work very well at the computer, these task-specific lenses offer larger optical areas for intermediate and near tasks such with the computer and reading.
Select one of the following topics for more information about eyeglasses from the Mission Eye Clinic:
> Understanding Your Eyeglass Prescription: Common Refractive Errors
> What to expect when you receive your new eyeglasses
> Proper Care of Your Eyeglasses
> We are especially experienced in eyeglass problems and difficult prescriptions