Glasses & Contact Lenses
Glasses: Protecting your Assets
In California, we are fortunate to be able to enjoy outdoor living almost year around. However, studies suggest that long hours of sun exposure may be dangerous to your eyes. Cataracts, skin cancer, macular degeneration and pterygium have all been implicated as consequences of UV (ultraviolet and invisible) radiation from the sun. Protection from UV-absorbent sunglasses and a brimmed hat are recommended whenever you are out in the sun long enough to get a suntan or sunburn. The variety of sunglasses for sale can be confusing. Sunglasses should block 99% of ultraviolet rays. The price of a pair of sunglasses and the material from which they are made are no indication of the effectiveness of UV filtering.
Color and darkness of lenses are no indication of the ability to protect. Tint color only affects the perception of color, so that dark grey or dark green tints probably allow the most normal color vision. Lenses that block all blue light are usually amber and make your surroundings look yellow or orange. This tint makes distant objects appear more distinct, especially in snow or haze. Darkness may be a risk if the lenses are not properly blocking ultraviolet rays. Since the pupil of the eye dilates in dimmer light, an unprotected eye would receive more than the normal dose of toxic rays if the lenses are dark.
Polarized lenses are great for reducing glare, especially for driving and boating. Although polarization does not block UV, they are usually combined with UV blocking substances to provide maximum comfort and protection. Mirror finishes, on the other hand, reduce the amount of visible light passing through, but are not fully UV repellent.
Although price is not the only feature, you can check lenses to determine if they are made properly. Non-prescription glasses may be held to look at a rectangular pattern, such as a floor tile or a window panel. At a comfortable distance, covering one eye, move the glasses side to side as well as up and down. The lines of the rectangle should remain straight, especially in the center of the lens. Lenses are not unbreakable, but they must meet impact standards set by the Food and Drug Administration. Plastic lenses are less likely to shatter than glass lenses, but plastic scratches more easily.
The natural human lens is an effective UV absorber. In the past, people who had undergone cataract surgery, in which the natural lens is replaced with an artificial intraocular lens, were at increased risk of UV damage. Currently, however, the materials used for this surgery are usually fully UV absorbent. Contact lenses are not necessarily UV absorbent, but are increasingly being produced with UV protection. In addition, there are certain drugs that make the skin more sensitive to light (photosensitizing). These include: psoralens (for psoriasis), tetracycline, doxycycline, allopurinol, and phenothiazines. In summary, the best sunglasses offer 100% UV absorption, contain a medium tint, and are of best optical quality. Yet they don't have to be expensive.
Most people suffer from some form of refractive error. Regardless how well one sees, there is some form of optical correction which will improve sight.
Some people are nearsighted, or myopic, so that their vision without correction is better up close than far away. This affects about 50 million Americans, supplying the vast majority of spectacle wearers and contact lens users. Almost all persons start with glasses. Spectacles, or glasses, are the easiest to use. Easy to put on and easy to remove. Simple to decide when to wear them, moment to moment. The lower the prescription power, the thinner the lens, the less the distortion of vision with spectacles. As lens power grows, thickness and weight increase, as well. Spectacles provide physical safety. Lenses are extremely shatter-resistant. Frames protect the eyes and the orbits from direct injury. Over time, glasses are usually a less costly form of vision correction.
While glasses correct vision well, contact lenses are increasingly popular. Contact lenses may correct nearsightedness, farsightedness (hyperopia), astigmatism or presbyopia (reading). Despite the mind-boggling assortment of lens systems on the market, not all patients can wear all lenses.
The first-time contact lens wearer may be of any age. Infants with congenital cataracts benefit from contact lenses after cataract surgery. This would be the only situation in which the contact lens wearer is not fully responsible for care and maintenance of the lenses. When asked if an adolescent is old enough to wear contact lenses, the answer is based on the child's ability to fully care for the lenses, rather than age.
Originally quite thick, few patients still wear hard contact lenses. These lenses provide excellent clarity, correct astigmatism and are very durable. Care and maintenance is simple and forgiving. Cost is low.
Rigid gas permeable contact lenses (RGPs) have generally replaced hard lenses. Made of state-of-the-art materials, these lenses also provide excellent vision, correct astigmatism and are very durable. Gas permeable contacts have an extended wear time. Most importantly, their nutritional permeability keeps the cornea much healthier, increasing safety. RGPs may be used for therapeutic care, as in keratoconus, corneal scars and corneal injuries. In color blindness, specially tinted lenses may provide some color perception.
All lenses have a finite life expectancy, and, in general, soft lenses must be replaced more often than RGPs. Soft lenses may be categorized as daily wear (removal every night), extended wear, astigmatic (toric), and planned replacement.
Standard daily wear soft lenses are replaced as the lenses become coated with deposits. A plethora of contact care systems greets the consumer at the store. Sensitive patients should consider non-preserved systems to minimize chance of allergy. Extended wear soft lenses were developed to extend, or increase, the wear time of soft lenses. While some patients may sleep in these lenses, the increased wear time often serves to allow more hours of daily wear. More recently, "disposable" lenses have come to market. Originally planned to diminish reactions to contact lens allergies and solutions, planned replacement lenses have become extremely popular. One variety provides daily wear lenses every two weeks. Another variety is kept in the eye 24 hours a day for one week, discarded and replaced with a brand new lens. More recently, daily disposable lenses have been offered as lenses to be discarded after each use.
More mature patients not only have to deal with their refractive error for distance, nearsightedness or farsightedness, but also the increased need for optical help at near, for reading. Provided in glasses with bifocals or multifocal progressive lenses, contact lenses also play a role. Contact lenses may be prescribed to correct distance vision while using reading glasses. To avoid glasses altogether, monovision or bifocal contacts may be tried. Monovision takes advantage of the innate difference in vision between the two eyes, leaving one corrected for distance and the other for near. In appropriate cases, bifocal contact lenses may be successful.
The notion that contact lenses are carefree devices is slowly giving way to the realization that these are medical devices that must be handled and worn with care. Used properly, contact lenses are relatively safe. On the other hand, if things go wrong, they can do so in a major way. It is known that the more hours a contact lens is worn, the greater the risk of infectious corneal disease. Contact lens wear, even on a daily wear basis, entails more risk than do spectacles. Scrupulous attention to wear and care routines and frequent follow-up examinations are necessary to avoid or minimize the risk of complications.