The presbyope has “trombone vision“—that telltale gesture of moving objects farther and farther away from the eyes in order to see them clearly. Most people opt for bifocal glasses or simply resign themselves to placing on a separate pair of glasses to read, sew, and do other tasks that require good close-up vision. However, there are several ways to correct this condition with contact lenses: bifocal contact lenses, “monovision” lenses, “compromise” contact lenses, having two pairs of contact lenses, and wearing reading glasses over contact lenses.

Bifocal Contact Lenses

Currently in the U.S. bifocal contact lenses are available in two types: conventional hard lenses and the newly released soft lenses. There are available basically two designs of either form of bifocal contact lens. Both of these, like spectacles, have two distinct powers, or prescriptions: one for near, one for far.

Crescent bifocal contact lenses most resemble bifocal eye-glasses. They have the prescription for distance at the top part of the lens, and the crescent-shaped segment at the bottom contains the prescription for close-up vision. As you gaze ahead normally, the distance power is used; as you gaze down, the near power goes into effect.

Because contact lenses naturally rotate on the eye during wear, some means of keeping bifocal lenses stabilized is necessary. Otherwise the crescent at the bottom would gradually drift toward the top where it would do no good—unless you held your newspaper over your head. These lenses are often weighted at the bottom with a thicker segment (prism), which utilizes gravity to keep the lens oriented. Crescent bifocals may also be truncated, a process in which the bottom edge is cut off to align it parallel with the lower eyelid margin. Another less effective modification that stabilizes bifocal lenses features orientation grooves cut into the top edge of the lens, providing a pathway for the inner surface of the upper lid to prevent rotation of the lens.

Like crescent lenses, concentric bifocal contact lenses also have two distinct powers, or prescriptions, but with a structural difference: the near prescription segment is in the shape of a ring acting as the outer rim of the lens; the distance power is a circle in the middle. With this lens, which resembles a bull’s-eye target, there’s no worry about its rotating on the eye. As with crescent bifocal lenses distant vision is effected by looking through the center, and near vision by looking down through the outer rim.

The best candidates for bifocal contact lenses are those who have been successfully wearing single-vision contacts for some time to correct myopia, hyperopia, or astigmatism. They will have the least problem with adjusting; but even so the success rate is low. The recent advent of the soft bifocal lens, however, should improve these statistics for the millions of presbyopes in this country, many of whom would no doubt be delighted to be able to wear bifocal contacts.

Fitting bifocal contact lenses is difficult (such factors as pupil size and lower lid position complicate the fitting process); manufacture of the lenses is more intricate than for the single-vision contacts; delivery time is slow; and the cost is necessarily higher than for conventional lenses. Many wearers report that bifocals are less comfortable than single-vision contacts, usually because the prism that prevents rotation adds bulk and makes the lens heavier.

New contact lens wearers not only have to adjust to lens wear in general but also have to adjust to the means of wearing a bifocal prescription. As in bifocal spectacles this involves learning how to adjust to the “jump” in vision that occurs every time you shift your gaze from near to far, or vice versa. Initially vision may be frustratingly poor —especially with hard lenses—during the adaptation period because the sensation of having a foreign body in the eye causes ocular physiological changes that lift the lower lid and the lens. Thus the bifocal segment is higher than it should be. Since this bifocal segment is so very small, there is very little tolerance in the proper positioning of the lens. As difficult as it is to achieve, perfect centering of the contact lenses is absolutely crucial for successful bifocal hard contact lens wear.

In response to these problems manufacturers are experimenting with design modifications. Multifocal or variable- focus contacts (available in hard and gas-permeable lenses) have not two, but many powers that gradually blend into each other, avoiding the annoying jump in vision. The lens contains all the different powers needed by the wearer to see clearly at any distance: near, far, and intermediate. The bifocal contact lens candidate will have to be patient and well motivated because it usually takes a few weeks until the lenses can be worn with comfort and provide good vision. Also some lens modifications and adjustments are usually the rule.

As many see it, the main advantage of hard lenses is that when fitted properly they provide the sharpest visual acuity for all the refractive errors—even better than spectacles can. It’s not uncommon for those who have nearsightedness, farsightedness, presbyopia, and most degrees of astigmatism to report 20/10 vision—that’s better than “normal”! Your prescription can be accurately ground into the front surface of a hard lens, and its smooth, firm, domelike undersurface, combined with the tears trapped beneath, forms a perfect refracting surface for the eye. A conventional soft lens, on the other hand, conforms to the shape of the cornea much like a tablecloth drapes over a table and so cannot completely correct astigmatism originating in the cornea. There are special new soft and gas- permeable lenses capable of correcting a relatively high degree of astigmatism, but hard conventional lenses are still the best for consistently correcting the higher amounts of astigmatism; besides, not everyone can deal with the soft lenses‘ disadvantages.

LOW COST

The next most popular plus is that standard hard lenses are the least expensive of all types of lenses. When properly handled and maintained they can last ten years and more. During that time tiny scratches and roughened edges that are bound to occur even during normal wear can be polished away at minimal cost. Also, the lens can be modified for any minor changes in prescription without ordering a new lens. Should you require a new lens, the prescription can be accurately duplicated and the lens can be replaced at minimal cost. In addition, the cost of cleaning and maintaining hard lenses is quite low.

CONVENIENCE

A lot of people who wear hard lenses like the fact that they’re easy to keep clean and don’t require the sterilization and special rinsing solutions that soft-lens care entails. With hardlenses all you do is rub a few drops of germicidal solution over the lens, rinse with plain tap water, and you’re done. This is especially important if you’re a frequent traveler who doesn’t need the extra weight and bulk of several bottles of liquid sloshing around your luggage. (Not to mention the mild annoyance of a thermal disinfecting unit, which may also require a hefty electric current adaptor in some countries.) A hard lens is also easier to handle than the floppy, slippery soft lens. This is particularly true for older people. Once you have the knack, insertion and removal are a snap.

ATMOSPHERIC CONDITIONS

Since the plastic from which they are made is hydrophobic (does not absorb water), dry air doesn’t affect the quality or the comfort of the lens.

COLOR

The fact that hard lenses can be tinted almost any color does more than enhance the color of your eyes. From a practical standpoint it makes them easier to retrieve when dropped, easier to locate when decentered, and reduces the light sensitivity and glare that may occur with clear hard-lens wearing. Most often hard lenses are tinted blue, gray, or green, but other tints are available.

VERSATILITY

Hard lenses have tremendous versatility. Most standard rigid lenses are corneal lenses, which fit over the cornea only. But scleral lenses exist too. These are large contact lenses that cover the white of the eye and are used for certain prosthetic and cosmetic purposes. Fenestrated lenses, which have tiny holes drilled through them, and vented lenses, which have tiny ridges carved in the undersurface to permit a better exchange of gases, allow greater tear flow.

There are also bifocal contact lenses. Special corneal cosmetic contact lenses can be used to provide an artificial color to the eyes. They’re useful for actors and actresses and others who would like to improve or intensify their eye color. The entire lens, except for the clear, central visual area, is painted or dyed until opaque. A red-tinted X-Chrom lens is also available, which allows the color-blind to approach near normal color perception. Another type of cosmetic contact lens is completely opaque, covers the cornea and sclera, and is used to provide a new appearance for a disfigured or damaged eye.

Though the eye is quite durable, it’s also an irreplaceable, delicate, sensitive, and highly sophisticated organ. Your eye is directly connected to your brain by the optic nerve and is closely related to other systems of your body. It shouldn’t be considered independently, and before you walk off with a pair of contact lenses you should undergo a complete medical eye examination by an ophthalmologist.

Such an exam is much more than a simple mechanical test of your eye as an optical instrument. It determines what prescription you’ll need. It also determines whether you’ll be able 26 to wear contact lenses safely and comfortably, and reveals clues that form a picture of your optical health and your physical condition in general. It also yields the measurements needed to “fit” you with the right pair of lenses—these measurements must be extremely accurate if you’re going to be comfortable wearing lenses. To do all this, your eye doctor uses a variety of instruments and techniques that may seem baffling and mysterious to the potential contact lens consumer. Space- age technology has invaded ophthalmology, and your eye physician’s examining rooms may resemble the inside of a spaceship; the instruments approximate cousins of Star Wars character R2D2, with futuristic beeps and digital readouts. Whether your doctor has the latest in equipment or not, the examination can be a fascinating process if you let it; and you should feel free to pepper him with questions.

History. This first step may seem casual and unscientific, but it’s very important. Your eye doctor will ask you “Why are you here?” and discuss with you your motivation, occupation, leisure activities, systemic diseases and medications, eye diseases and medications, and allergies, complaints about your vision, whether you get headaches, and whether you’ve worn contacts before, what type they were and any problems you had while wearing them. (If you do wear contact lenses, you should keep them out of your eyes at least twenty-four hours before your exam, though seventy-two hours is preferable.)

Refraction. This step determines the prescription your lenses will need to correct whatever refractive error—nearsightedness, farsightedness, astigmatism, or presbyopia—you may have. We’ve come a long way from the days when a simple wall eye chart sufficed. Nowadays the doctor usually first instills special eye drops that dilate your pupils before using the two instruments, the Phoroptor and the retinoscope, to come up with your lens prescription.

First comes the Phoroptor, that familiar contraption that makes the examinee look like the ultimate bug-eyed Martian. As you gaze at the eye chart (projected on the wall), the physician tries out several lens combinations, repeatedly asking you “which is better, first or second?” Out of its billions of possible lens combinations, the examiner determines and fine-tunes your prescription. After this subjective test (you’re judging which lens corrects the best), the results are read off the Phoroptor in order to check the prescription by doing an objective test for refraction. As your eyes gaze at a distant target through the prescription in the Phoroptor, the doctor peers into your eyes with the retinoscope. Through the dilated pupils the light of the retinoscope creates a measurable shadow and light movement on your retina, which enables him to check the accuracy of the prescription.

Curvature of the Cornea. Using a keratometer, an optical scanning device, the ophthalmologist determines the exact “topography” of the cornea. A system of mirrors measures the horizontal and vertical meridians of the cornea. This determines the steepness or flatness of the cornea and its degree of corneal astigmatism, an important part of the overall refractive error picture, and instrumental in determining whether you need a hard or soft lens.

Muscle Range and Coordination. How well do your eyes work together? Do they point to and focus at various distances equally? How well do you judge distance and space (depth perception, or stereopsis)? To find out, the eye doctor uses a muscle light and special prisms.

Outer and Middle Layers of the Eye. Next comes the slit lamp, an electrical microscope that lights up and magnifies your eyelids, cornea, iris, lens, and fluid of your eye in order to reveal any disease, damage, inflammation, or other abnormality. A special stain called fluorescein is used in conjunction with a cobalt-blue filter to detect any corneal defects or abrasions not visible with the naked eye.

Inner Layers of the Eye. Through the dilated pupil, the retina and its blood vessels can be seen with an ophthalmoscope, which illuminates and enlarges the doctor’s view. This is the point at which early signs of diabetes, hardening of the arteries, hypertension, and other general disorders of the body can be detected.

Eye Pressure. This is the “glaucoma test.” The doctor anesthetizes your cornea with special eye drops, and measures the pressure of the eye fluid with a tonometer. Though the instrument actually touches your cornea, you don’t feel a thing because of the anesthetizing eye drops. This test is especially important for anyone over the age of thirty, although it is unusual for glaucoma to occur before the age of forty. There is also a “noncontact” tonometer which utilizes a puff of air to measure the eye pressure. Although not as accurate as a tonometer, this instrument is an excellent screening device and eye drops are not instilled.

Tear Function. Tears lubricate and cleanse your eyes and also provide the cornea with oxygen. A sufficient supply of tears is a must for comfortable contact lens wear. “Dry eyes” can be countered with special eye drops if the problem is slight. To make sure it isn’t a contraindication, the ophthalmologist performs the Shirmer test: special strips of paper placed under the lids to gauge the amount of tear production. After about five minutes the test strips are removed and the amount of tear absorption is measured and evaluated.

Visual Field. In certain instances (suspicion of glaucoma, retinal abnormalities, optic nerve disorders, neurologic disorders, headaches, and so on) a test of your peripheral vision is important. To measure your peripheral (side) vision, a special computerized instrument is used. (If you like video games, you’ll love this part of the test. If you don’t, the challenge may leave you a bit limp.) First each eye is tested separately, then together. Your head is kept immobile as you face a large dome, perforated with a scattering of pin-sized holes. As you gaze ahead steadily at a red-lit cross in the center of the dome, minuscule flashes of light go off through the holes, one at a time, at various distances from the center cross. Every time you see a “star” light up in this mini-planetarium, you hit a button; meanwhile the computer keeps score by adding up the correct “strikes.”

Your ophthalmologist will evaluate all the information thus gleaned from all parts of the ocular examination and decide whether or not you—and your eyes—are a good candidate for contact lenses, and if so, what type. Those who “pass” the exam then go on to the next step, the contact lens fitting.

Nearsightedness (Myopia). This occurs when the eyeball is too long for the lens’s focal capacity. The patient’s cornea and lens focus the image of a distant object in front of the retina, so vision is blurry except when looking at nearby objects. Myopia affects one quarter of the world and seems to be on the rise, though it’s a mystery why. Most contact lens wearers are myopes.

Farsightedness (Hyperopia). This occurs when the eyeball is too short. As a result the lens of the eye can’t bring near objects into focus by the time the image reaches the retina. (Theoretically the focal point is behind the retina.) Therefore close objects are blurry, and distant objects are clear. In mild cases distant objects are seen clearly enough so constant visual correction is not required. In severe cases distance vision may also be affected, so the hyperope needs to wear some form of vision correction constantly; these are more likely candidates for contact lenses, though the percentage is far lower than for myopia.

Astigmatism. This is a bit harder to understand. Astigmatism is a refractive error that usually results from a cornea that isn’t perfectly round, but shaped more like a football than the usual basketball shape. Imagine the cornea as a dome divided into segments by lines drawn across its surface that intersect at its center, like the segments of an orange. The normal eye, with a spherical cornea, has the same curved lines all around. The astigmatic’s  aspherical cornea has differently curved lines like one half of a lemon, with any given line either flatter or steeper than the one perpendicular to it. Therefore the vertical and horizontal components of both near and far images can’t focus together. As a result the image appears blurry. Occasionally the crystalline lens—not the cornea—is at fault in astigmatism. Astigmatism is very common and often occurs in addition to myopia or hyperopia.

Presbyopia. This is part of the aging process (usually after the age of forty) and is due to the gradual loss of elasticity of the crystalline lens of the eye. As the lens loses its flexibility, one has more and more difficulty focusing on nearby objects. You’ll know your eyes are “getting old” if your arms seem too short when you read, or if you have trouble performing close-up tasks like threading a needle. Presbyopia will occur in addition to the “Big Three”—myopia, hyperopia, and astigmatism—but pure presbyopes only require a correction during close-up tasks.

Nearly half our population has one or more of these refractive errors. Fortunately all of them can be corrected witheyeglasses or contact lenses. In nearly all cases the contact lens does it better.