Eyeglasses, Sunglasses, and Magnifiers (cont.)
Trifocals and variable lenses
Some people will require multiple distances or focal lengths for a wide variety of tasks, including near and intermediate tasks. Near tasks include reading and sewing, while intermediate tasks include computer use or reading piano music while performing, for example. When presbyopia advances, our eyes lose the ability to see intermediate as well as near items. For these special needs, a trifocal lens may be required. This allows for clear distance, intermediate, and near vision. The trifocal lens is generally placed in the same location as the bifocal, with a smaller segment closer to the center of the lens.
A further advance is the variable focus lens, in which the lines between the bifocal and the distance lens are eliminated, providing a gradual transition from near to far. Varilux is a common brand name among numerous others. Many people prefer these more expensive lenses because the transition line is so annoying. It may take several weeks to become accustomed to this type of lens. These lenses provide the intermediate distance in the region between the bifocal and the distance segments, thus creating a trifocal capability as well.
In some cases, customers may also be asked for the "pupillary" distance. This is actually the interpupillary distance, the distance between the pupils (the openings) of the eyes. This distance is usually measured in millimeters.
We do not recommend nonprescription glasses as a permanent solution to significant eye problems because they usually are not as accurate as prescription lenses. In addition, the use of OTC glasses could lead to the postponement of an eye examination that could reveal a serious underlying problem. However, OTC glasses are okay to keep as "backups" for times when prescription glasses have been misplaced or are being repaired.
Sunglasses
Sunglasses that can be purchased without a prescription come in
hundreds of models with varying shapes, materials, and colors.
A must-have feature for all sunglasses is complete (100%)
protection against the potentially damaging effects of the
sun's ultraviolet-A and ultraviolet-B rays. Avoid buying dark
sunglasses that do not offer 100% UV protection. Dark glasses
prompt the pupil of the eye to dilate (enlarge), allowing UV rays to
enter. So, if dark glasses lack complete UV protection, they can
promote damage to the eye.
Ultraviolet rays are well-known causes of the following eye conditions:
- Macular degeneration: in which the pigment cells in the center of the retina slowly change during the dry form of this disease, creating distorted vision. The rapid form, or wet macular degeneration, can lead to sudden vision loss.
- Cataract: in which the clear crystalline lens of the eye develops progressive clouding and opacity. People from high altitudes, equatorial regions, and those with outdoor occupations generally develop cataracts at a younger age due to increased lifetime UV exposure.
- Pterygium: in which the clear surface membrane (conjunctiva) overlying the white part of the eye (sclera) gradually becomes cloudy and elevated, then grows toward the center of the cornea. Advanced cases can lead to vision loss. Once again, people from equatorial regions are much more likely to develop pterygium.
- Basal cell carcinoma: in which abnormal skin cells turn cancerous, particularly on the lower lids where there is more UV exposure than the upper lids. When detected early, basal cell carcinoma of the eyelid can be cured with surgical excision.
- Squamous cell carcinoma: in which abnormal conjunctival cells form a cancerous growth on the surface of the eyeball. This tumor type is more dangerous and invasive than the more common basal cell carcinoma, and
it also benefits from early detection.
Some favorable features that consumers should be aware of include
the following:
- Polarization: Polarized sunglasses reduce glare from snow,
water, highways, and other reflective surfaces. Consequently, wearers
see better and squint less. These advantages can be crucial to
automobile drivers, airline pilots, heavy-equipment operators, and
athletes.
- Impact resistance: Impact-resistant sunglasses resist
breakage when dropped or mishandled. Glasses made of a trade-name
plastic called CR-39 are lighter than glass and more impact-
resistant. Glasses made of high-index plastic are even lighter than
CR-39 glasses. In addition, these lenses have a coating that protects
them against scratching.
- Photochromicity: Photochromic sunglasses have lenses that brighten or darken in response to the intensity of sunlight. This transitional lens treatment does not in and of itself provide UV protection, a common misconception. Thus, be sure to look for the UV protection rating of photochromic lenses as a separate value.
- Water-sheeting: Lenses with this feature help preserve
visual acuity when water (from the rain, the sea, waterfalls, etc.)
strikes the lens. With water-sheeting, the water forms in a see-through sheet on the lens rather than individual droplets that
block or distort vision.
Next: Magnifying glasses »
- Cataracts - Learn about cataracts and how they form. Discover cataract symptoms, treatment options, tests, signs and causes. Find out how it relates to other eye disorders, such as glaucoma and macular degeneration.
- Eye Care - Get information on eye care tips and eye health, disorders and treatment with OTC eye-care products, and when to see an ophthalmologist about an eye infection or condition.
- Macular Degeneration (Age-Related Type) - Read about age-related macular degeneration (AMD, ARMD) causes, symptoms, diagnosis, risk factors (hereditary), treatment, research and vision loss statistics.
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