A. If they are, something is wrong. Contact the fitter at once.

Q. Can you tell that someone is wearing contact lenses?

A. Usually not.

Q. Can they be coloured?

A. Yes. Lenses can be tinted almost any colour.

Q. Is that expensive? A. No.

Q. I’m worried about lenses slipping round behind my eyes. Does this often happen?

A. No, never, It’s impossible!

Q. I need glasses for reading only. Would I be suitable for contact lenses?

A. No. Stick to your glasses.

Q. I have astigmatism. Does this mean I can’t wear contact lenses?

A. Not at all. Hard lenses cover astigmatism. It is even possible to have special soft lenses for astigmatism.

Q. What is spectacle blur?

A. Temporarily blurred vision in glasses after wearing contact lenses.

Q. Is that serious?

A. No. Not unless very severe and persistent.

Q. What causes it?

A. Either a moulding of your corneas into a new shape, or a slight swelling from accumulation of fluid in the corneal outer layer.

Q. My friend wears very thin, hard lenses. Is that a good idea? A. The smaller the better, so long as they give good vision.

Q. She says she never gets spectacle blur. Why is that?

A. Very small lenses are less liable to cause this, because the corneas have a better oxygen supply.

Q. Why is oxygen important?

A. Corneas, like all living tissues, need oxygen to survive. As they can’t get it via the blood because they do not contain blood vessels, they have to get it direct from the atmosphere.

Q. What happens if I get a bit of grit behind a contact lens? A. You will know all about it. This doesn’t happen often.

Q. What should I do?

A. Take out the lens and wash it.

Q. But suppose the grit stays in my eye?

A. Get someone to remove it with the corner of a clean handkerchief, or see your doctor. Don’t use your lenses meantime.

Q. Is it very difficult to insert and remove contact lenses?

A. The difficulties in insertion are largely psychological. Removing lenses is easy, but it takes a bit of practice to learn todo it quickly.

Q. Is it a good idea to use a rubber sucker to remove lenses?

A. No. Not unless you can be certain that the lens is on the cornea.

Q. I am long-sighted, 45, and beginning to have pr^oblems reading. Also, my distance vision is sometimes a little blurred. Do you recommend contact lenses?

A. Yes. They should solve all your problems for a number of years. Eventually, of course, you will need reading glasses as well as contact lenses, but you will be spared bifocals.

Q. Is it true that contact lenses can prevent short sight from progressing?

A. No.

Q. Is it true that short sight can be cured by an operation on the cornea?

A. The procedures are dangerous and the effect often temporary. Permanent damage may occur. Not recommended.

Q. Shall I require to change my contact lenses as often as I change my glasses?

A. No. Much less often. You may save money in the long run.

Q. I sometimes see double with one eye when wearing my lenses. Is this serious?

A. This suggests that one lens is not centring properly. Not serious, but you should tell your fitter.

Q. My vision often fogs up but clears when I blink. What should I do?

A. Blink more. Contact lens wearers sometimes get into a bad habit of inadequate blinking. Make sure you don’t!

Q. Why is it important to put the plug in the sink when washing my lenses?

A. If you drop the lens you’ll never retrieve it!

Q. Do you recommend tinted lenses?

A. Yes, but not too deeply tinted. Tinted lenses relieve the light sensitivity that most wearers have, initially. They are also easier to find if dropped in water.

Q. Can I use a clean tissue to clean my lenses? A. No. Tissues always cause scratching.

Q. What should I use then?

A. Your finger tips — thoroughly washed first, of course.

Q. Is it easy to insert contact lenses in someone else’s eyes?

A. Very. Easier than putting them in your own — providing they will keep their eyes open properly.

Q. My mother has had cataracts removed. Could I learn to put in and remove her contact lenses for her?

A. Very easily. The specialist will be delighted to instruct you and your mother will bless you!

Q. What is the difference between an ophthalmic optician and an optometrist?

A. No difference.

Q. Who may fit and prescribe contact lenses?

A. An ophthalmic optician, an ophthalmic medical practitioner or an ophthalmologist.

Q. What is an ophthalmologist?

A. A doctor who is a specialist in the disorders of the eye.

Q. Whom should I see if I have major complications from contact lens wear?

A. An ophthalmologist. Your family doctor will refer you.

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.

Soft lenses‘ raison d’être can be easily summed up in one word: comfort. If hard lenses can be compared to a new pair of shoes, soft lenses seem to fit like an old pair of broken-in sneakers. Many wearers claim they don’t feel a thing, and are completely unaware of them from the word go. Hard-lens wearers who had previously given up on these lenses are especially astounded by the lack of eye sensation because they have something with which to compare the soft lenses. No wonder more than half of all the new contact lenses that are sold are soft! And the percentage is increasing, although not quite as fast as a few years ago.

The soft revolution in contact lenses began over twenty years ago in Czechoslovakia, when chemist Otto Wichterle began experimenting with a plastic called HEMA (hydroxyethylmethylmethacrylate). HEMA had been used in surgery because of its compatibility with human tissue; it seemed to be a good candidate for contact lens material because it was also optically clear. Working in his kitchen with equipment he constructed from his children’s Erector set, Wichterle concocted the first soft contact lenses. After testing was completed, more efficient and sophisticated production lines were set up. The rest, as they say, is history. The new soft lenses seemed like a cure-all—the lenses were comfortable, and in most cases the vision was good.

New Developments in Soft Contact Lenses

The first soft lenses became available in the United States in 1971. To say there have been some changes made since then would be an understatement. The original and still highly popular Bausch & Lomb Soflens was (and still is) spun-cast of good old HEMA. But the field of soft contact lenses is a lively, dynamic, ever-changing one, with new lenses constantly coming into the market. There are now dozens of brands—numerous types of plastic whose chemical ingredients roll trippingly off the tongue (2-hydroxyethylmethacrylate, N-[1, 1-Dimethy1-3- oxobutyl]-Acrylamide and Methacrylic acid is an example). These plastics differ entirely from the synthetic material of hard contacts. Unlike PMMA, which is basically comprised of a single monomer (a substance made of low-weight molecules), soft, or hydrogel, contact lenses are made of various polymers (compounds of high molecular weight derived by combining many smaller molecules, such as monomers). These polymers, most of which are still based on HEMA, are made from a selection of at least eight different components, plus several “crosslinking” agents that bind the polymers together. The physical properties of hydrogel materials resemble living tissue more than any other class of biosynthetic material. Various methods of manufacture have also been developed, including lathe-cutting (the plastic is ground while in a hardened state) and mold-casting.

The impetus for all this ongoing activity springs from the remaining imperfections of the soft contact lens. Although a remarkable breakthrough, the soft lens is by no means a cure- all and cannot be worn by everyone. Thus the drive for improvement continues. For example, the industry is making significant headway with astigmatism and bifocals, heretofore huge flies in the ointment as far as contact lenses were concerned. The new soft toric lenses enable soft-lens wearers with appreciable amounts of astigmatism to see more sharply than with traditional soft lenses. (However, they still do not provide the crispness of vision that a hard lens can provide.) In the fall of 1981 soft bifocal lenses first became available to the public. For those who can’t achieve normal levels of comfort, wearing time, and visual acuity with soft lenses, super-thin soft lenses may be the answer. Another improvement involves a special coating that retards the accumulation of protein deposits on the soft lens’s surface, while improving the water-retentive properties. Such deposits are a major factor in shortening the life of soft contact lenses.

As shown in the smaller drawings for each type of refractive error, corrective lenses work by compensating for the eye’s deficiencies. In the case of myopia, where the eyeball is too long, the total refractive power of the eye is greater than is required for an eye of normal length. The rays of light come into focus before they reach the retina. A concave lens (thicker at the edges, thinner in the center) is used to focus the image farther back, on the retina. This is also called a minus lens because it causes the light rays to diverge or bend outward, in effect weakening the total refraction. A hyperopic eye, where the eyeball is too short, has a refractive power that is less than that of a normal eye. The light rays don’t focus until they’ve fallen behind the retina. This condition requires a convex lens (thicker at the center, thinner at the edges) to bring the focus point forward, so it lands on the retina. This is also called a plus lens because it converges the rays, making the total refractive power of the eye stronger. A presbyopic eye also requires a convex lens, which is often prescribed in the form of bifocals. (Yes, they can make bifocal contact lenses.) Astigmatism requires special curves in the lenses that focus the rays of lightat a specific axis.

A contact lens, with the layer of tears trapped beneath it, works by canceling out the refractive error. In effect it becomes another layer of the eye. It may be considered a prosthesis, or artificial body part, which actually becomes an integral part of the wearer’s optical system. Since it is placed directly on the living eye, it must go far beyond having the correct prescription; it must fit the cornea well enough not to interfere with the normal metabolism of the eye.

Of primary concern is the amount of oxygen that reaches the cornea, which is normally supplied by the air and the tears in exchange for waste carbon dioxide. Since every lens in use acts as a barrier against both the tears and the air reaching the cornea, contact lenses are designed and fitted to overcome this problem. Though the eye can adapt somewhat, a too-diminished gas exchange radically alters the metabolism of the cornea and its health will suffer. The primary effect of such suffocation is edema, a swelling of the cornea that can be likened to a blister on your skin. Edema may lead to more serious injuries to the delicate cornea, and is the most prevalent of all contact lens side effects. The race to design a better contact lens is now largely a battle against the oxygen barrier.

In designing a contact lens, there are two ways to increase the gas exchange and prevent or reduce edema:

THROUGH THE TEARS

With each blink the eye trades new tears for old. By improving the tear-pump mechanism, more spent, carbon dioxide-rich tears are alternately forced out from under the lens and more fresh, oxygen-rich tears are injected.

In order for the tear pump to work, contact lenses must be able to move slightly with each blink. Both soft lenses and hard lenses float on a thin layer of tears.

THROUGH THE LENS ITSELF

In gas-permeable lenses special materials (silicone and cellulose acetate butyrate) allow gases to pass through the lens material. In soft contact lenses the lenses themselves absorb the tears in which the oxygen is dissolved and transmitted to the cornea.

Ideally, both mechanisms should operate because even in gas-permeable lenses the oxygen transmission is not 100 percent. In addition to supplying oxygen, tears also meet other requirements of the cornea, such as lubricating the corneal surface, flushing away foreign bodies, and preventing infection because of its lysozyme content.

In conventional hard lenses oxygen is supplied mainly through the tear pump. In some cases fenestrations, or tiny holes drilled into the lenses, can make them somewhat gas permeable because air can pass through the holes. Making lenses smaller and thinner increases the tear supply; so can the use of drops of artificial tears. As frivolous as this sounds, proper blinking is crucial for proper tear flow and contact lens comfort.