Sixty percent of the 161 million Americans who wear prescription eyewear choose eyeglasses. Wearing eyeglasses is one of the simplest ways to correct vision problems.
To see images clearly, light rays must focus directly on the retina, the light-sensitive nerve layer that lines the back of the eye. There are different kinds of focusing problems, called refractive errors, which may require corrective lenses. In the case of myopia or nearsightedness, the eye is too long. Light rays focus before reaching the retina and images appear blurry. In hyperopia or farsightedness, the eye is too short, so light rays have not yet focused when they reach the retina. Astigmatism describes an eye with a cornea that is oval shaped instead of round, causing light rays to hit the retina in more than one place.
Eyeglass lenses compensate for an eye that is too long or too short by adding or subtracting focusing power. The lenses create just the right amount of focusing power so light rays focus directly on the retina.
A plus (+) in front of the first number of the eyeglass prescription means the lens corrects farsightedness. A minus (-) in front of the first number means the lens corrects nearsightedness. If a second and third number are present in the prescription, they indicate astigmatism. The higher the first number in the prescription, the greater the correction in the lens.
Lenses are available in glass, regular and high index plastic, and polycarbonate. Although they scratch less easily, glass lenses tend to be heavier and often slide down the nose. Plastic and polycarbonate lenses are lighter and safer than glass but scratch easily. Scratches cannot be removed but they can be avoided or minimized with appropriate care. Scratch resistant coatings can be applied to plastic and polycarbonate lenses but some of these coatings crack if exposed to extreme heat or cold.
Frames come in many shapes and sizes, so it is important to pick a frame that is best for you. Factors to take into consideration when selecting a frame include facial features, age, activities and the prescription itself. Often a strong prescription requires thicker lenses, which can affect your choice of frames.
Ask about the quality and expected lifetime of the frame and if there is a frame guarantee.
Sunglasses are popular for comfort and fashion, but now there is medical evidence supporting the use of sunglasses to protect the long-term health of the eyes.
More than a dozen studies have shown that spending hours in the sun without proper eye protection can increase the chances of developing age-related eye diseases like cataracts and macular degeneration. Ophthalmologists now recommend wearing UV-absorbent sunglasses and brimmed hats when in the sun long enough to get a suntan or sunburn.
People mistakenly confuse the ability of sunglasses to block UV light with the color and darkness of the lenses. In truth, UV protection comes from a chemical coating applied to the surface of the lens. Shop for sunglasses that absorb 99 or 100% of all ultraviolet (UV) light. Some lens manufacturers’ labels say “UV absorption up to 400 nm.” This is the same thing as 100% UV absorption.
In addition to UV light, sunlight also has low levels of infrared rays. Infrared wavelengths are invisible and produce heat. The eye seems to tolerate infrared well. Research has not shown a connection between eye disease and infrared light ray exposure.
Polarized lenses cut reflected glare, like sunlight bouncing off water, pavement, or snow. Sunglasses with polarized lenses are popular and useful for fishing, driving, and skiing. Polarization has nothing to do with UV light absorption, but many polarized lenses are now made with a UV-blocking substance.
Wraparound glasses are shaped to keep light from shining around the frames and into the eyes. Studies have shown that enough UV rays enter around ordinary eyeglass frames to reduce the benefits of protective lenses. Large-framed, close-fitting wraparound sunglasses protect the eyes from all angles. Wraparound sunglasses should be considered by commercial fishermen, mountain climbers, skiers, or anyone who spends time at high altitudes or on the water.
EXTENDED-WEAR CONTACT LENSES
Some people do not consider wearing contact lenses because they think the required cleaning, disinfecting, storing, and inserting are too much trouble. They may also want the option of occasionally napping or sleeping with their contacts in their eyes.
Extended-wear contacts are designed to appeal to these people. They require less maintenance than daily wear lenses and because they are thinner and allow more oxygen to reach the eyes, they may be left in the eye overnight.
To use extended-wear contact lenses, you must be free of external eye disease, have normal tear function, and be motivated to take care of them.
Infection is the most significant complication of extended-wear contact lens use. They must be removed at least once a week and thoroughly cleaned and disinfected. Many studies show the cornea is put at increased risk of infection by wearing contact lenses overnight. The risk of developing an infection in the cornea is 10-15 times greater for those who wear extended-wear contacts overnight than for those who use daily wear soft lenses. This risk increases with the number of consecutive days the contacts are worn overnight. Infections may range from simple conjunctivitis to blinding endophthalmitis, which is a serious infection that travels through all layers of the eye.
The decision to accept the risks and benefits of extended-wear contacts requires a process of evaluation between you and your doctor. Once you are carefully fit for your contact lenses, follow-up exams with your ophthalmologist to ensure continuing eye health is important. As with any contact lens, extended-wear contacts should be removed at the first sign of redness or discomfort.
Many types of tinted contact lenses are available. They can enhance and even change the color of one’s eyes for cosmetic purposes, for costumes, or provide special effects for the movie industry.
Tinted contacts can make light eyes more blue, green or hazel. They can alter the color of the eyes, such as making brown eyes blue.
Tinted lenses have been used in the movies since 1939. In the movie “Ghostbusters,” actors playing gargoyles wore red contact lenses. Reptile lenses were crafted for the commander in “Star Trek” and white contact lenses were used for the Hulk in “The Incredible Hulk.” Recently, these costume lenses have become available to the general public.
Tinted contacts may also be used to disguise or improve the appearance of an abnormal eye. They can be used to conceal corneal scars, irregular pupils and to hide shrunken, unsightly eyes. Sometimes tinting a lens can make the lens easier for a person with poor vision to handle. These tints are more subtle handling tints.
Contact lenses for the general public, including those with no correction, are considered medical devices. They must undergo clearance for safety by the Food and Drug Administration (FDA). Color additives used by the manufacturers of costume contact lenses must also be approved for use. Additives in unapproved lenses may be toxic.
Purchase only tinted contacts prescribed by an ophthalmologist, and never share lenses with someone else.
HOW TO CARE FOR CONTACT LENSES
The key to avoiding the irritation and infection sometimes associated with contact lens wear is proper cleaning.
There are two main types of lens care systems: heat and chemical disinfection. The appropriate choice depends on the lens type, duration of lens wear and an individual’s own biochemistry. Regardless of the type of disinfection system you choose there are a number of common steps that must be followed:
- Always wash your hands prior to handling your contact lenses.
- Remove one lens and place it in the palm of your hand. Apply a few drops of a contact soap, usually called cleaning solution. Rub the soap onto both sides of the lens surface to help remove deposits, debris, protein build-up, and any bacterial film. Removing surface deposits and other debris not only contributes to improved vision and comfort but also reduces the risk of infection and allergy. Soft extended-wear contacts may be the most likely to develop a protein build-up that can lead to lens-related allergies.
- After thoroughly cleaning the lens, rinse it with commercially available sterile saline solution. Homemade saline solutions have been linked to serious eye infections and should never be used.
- After cleaning and rinsing, lenses need to be disinfected. You and your ophthalmologist will pick the best system for you, but make sure you understand the instructions and follow them. Heat and chemical disinfection methods each require several hours of disinfection time.
- After disinfecting, rinse the lens with sterile saline before putting it in your eye.
- Your empty contact lens case should be thoroughly rinsed with warm water and allowed to air dry. All contact lens cases need to be cleaned frequently, including disposable lens cases.