Note: Here's the Edited Version of this entry

If your eyes aren't as good as they should be, contact lenses (or 'contacts' in short) are a fourth option to wearing glasses, undergoing laser treatment, or living on with poor vision.

Contact lenses are small transparent pieces of plastic which fit right onto your eyes and correct deficiencies which are due to less-than-optimum geometry. They are a foreign body to the eye, therefore some time is required to come to terms with them. It is a matter of one's individual metabolism whether the first contact with contacts creates bloodshot eyes and buckets of tears, or whether nothing special happens at all. Some people never get accustomed to contacts, while others do not want to ever live without them, but it is definitely worth giving it a try.

Some advantages of contacts over glasses are:

• They don't become covered with moisture upon entering a house in winters.
• Raindrops and children's fingers don't reach them.
• They feature unobstructed vision over the full field of view.
• They follow the movement of the eyes, hence there is no degradation of focus if looking to the side.
• You've got the freedom to wear sunglasses over contact lenses.
• Doing sports is feasible without the trouble of sweat dripping on your eyeglasses.
• There is hardly any diminution or enlargement of the image, as is the case with eyeglasses.
• They are practically free from parasitic reflections¹ -- in contrast to even the best glasses that money can buy.

Some Facts About Contact Lenses

Contacts can be classified with regard to several aspects: wearing and replacement cycle, consistence, and cut. So you can have 'continuous wear' soft lenses without optical correction, or 'daily wear' RGPs (see below) with bifocal cut, or almost any other combination of properties.

The history of contact lenses dates back to the year 1508 when none other than Leonardo da Vinci conceived the idea. But it was as late as 1887 that contact lenses became a reality. Following the common exponential curve of technology progress, hard plastic contacts were invented around 1936, soft lenses were invented in 1960 and were available on the market in 1971. RGPs appeared in 1979, and all the varietes of special cuts, disposables etc. appeared in the 1980ies.

Wearing And Replacement Cycles

The wearing cycle of a lens type mostly depends on its permeability to oxygen. Because there are no blood vessels, the cornea and eye lens feed on proteins and limited amounts of oxygen supplied by the tear fluid, and oxygen delivered by the surrounding air. Less permeable contact lenses must be taken out overnight because no tear fluid is being produced while sleeping².

• Daily Wear lenses are to be cleaned once a day, and must be taken out overnight.
• Extended (or Continuous) Wear lenses can be kept non-stop in the eye for up to 30 days before they require cleaning. Application fields are people with very poor eyesight who wouldn't find the storage box without their help, people who need to be ready for action on short notice at any time (like firefighters), and people who just like the convenience. Or if you frequently dream of lottery results, but can't identify the numbers.

The replacement cycle is the amount of time which can pass before a set of contact lenses is being replaced by a new one. Lenses which can be used for a period of up to two weeks are called disposables, whereas frequent replacement lenses last for up to three months.

Consistence

Contact lenses can be soft or hard-flexible. Soft lenses are made from a floppy plastic and contain some 40% to 75% of water. In general, they are more comfortable than hard-flexibles and are easier to get used to (in most cases this is a matter of minutes rather than weeks). On the other hand, their material is less permeable to oxygen. Their porosity renders them prone to deposits of proteins and particles as well as the intrusion of bacteria. Therefore soft lenses require somewhat more careful cleaning or a short replacement cycle.

Hard-flexible ones are made from a rigid type of plastic. They are also called RGPs which stands for rigid, gas permeable, in order to point out the main difference from the old 'hard' ones. They need some four weeks to gradually getting used to wearing them.

The 'hard' lenses of the 1970ies did not pass enough oxygen to the eye and are nearly extinct now.

Special Lens Cuts

• Bifocal lenses which have two sections, one to correct distance vision and the other to correct near vision.
• Special shapes to offset astigmatism ³.

Other Options

Apart from the aforementioned, you may order some special transparency functions, such as

• UV-blocking lenses, which are a supplement to, not a replacement for sunglasses, because they do not cover all of the eye.

• Polarized lenses, which act similar to polarizing filters in photography by suppressing light reflections from shiny surfaces.

• Slightly tinted lenses which attempt to enhance colour contrast in the scene that you see⁴.

• 'Special effect' lenses to change the colour of your eyes or let them look like those of a cat or an alien. This may be a good suggestion for Halloween, if you want to increase your chances with the opposite sex, or if you happen to be a Cosa Nostra boss.
  You should carefully study the smallprint on whether it is allowed to use them while driving a car, because some types have only a small portion in the center which is fully transparent.

Rigid Gas Permeable Lenses (RGP)

Wearing RGPs makes up an optical system that consists not of two, but of three components: of course, there is your own lens, and there is the contact lens. The third component is in between: tear fluid. This is essentially water which also has a refraction index, ie: a lens made of tear fluid is a lens in terms of optics. This has a number of consequences:

• The first set of lenses never fits. Because of the water layer this is always a matter of trial and error. But at least in Germany  you only pay for the final set.

• RGPs do not sit still on your eyes. Instead, they follow the lid in its upward movement, and settle down some fraction of a second later. This is necessary to exchange tear fluid and supply new 'food' for the eye lens. This constant movement of the RGP is something one has to get used to. If driving a car at night, the outer rim of the RGP tends to reflect a fraction of light from the car in behind into your field of vision, and due to the RGPs movements some shimmering lights seem to 'hover' somewhere ahead of you. This sounds more uncomfortable than it actually is, and it is nothing in comparison to all the reflections encountered even with eyeglasses with antireflective coating.

• To a certain extend, astigmatism is being corrected by the fluid which fills the gap between the RGP and your eye's lens. People with a light case of astigmatism can save the extra expense for fully corrective lenses.

Adaption from near vision to far vision is acomplished by a muscle which stretches the soft body of the lens. If an RGP is attached to the lens then the curvature of the outer aperture takes less effect, since it is being offset by the tear fluid in the gap. Wearing RGPs therefore cuts this near/far adaption ability in half, at least until the muscle has learned to double its effort. People of 40-something years start losing this ability anyway, and develop difficulties in close reading (this is called presbyopia in medical terms), so RGPs may not be the best choice for them.

Hygiene and Cleaning

Keep in mind that contacts are foreign bodies which are kept in direct touch with mucous tissues. The gap between a contact lens and the eye lens can easily become a home for germs and fungi if hygiene is not painstakingly maintained. Therefore it is best to strictly follow the smallprinted instructions that accompany every bottle of cleansing agent, or package of disposables, respectively. So one should carefully clean one's hands before touching contact lenses, and close all fluid bottles immediately after use, and one should not touch the tip of any of these bottles, nor use saliva as a cleansing agent (there are more life-forms in your mouth than in a gen-lab!). Home-made saline fluid, even if made from distilled water, is not sterile.

Cleaning solutions are specially matched to their respective lens type. You wouldn't want to accidentally wipe away some coating off your contacts with some abrasive cleaning fluid. Therefore do not switch to a different type (or different brand) of cleaning fluids without contacting your eye practitioner in advance.

'Daily wear' lenses are to be kept over night in a disinfection fluid, and need daily cleaning. Once a week they need some extra treatment which consists of putting them into a special encymatic cleaning fluid for half an hour, in order to remove deposits which originate from the tear fluid.

Contact Lenses and Cosmetics

• Some components of perfumes and eau de cologne can affect contact lenses, therefore they should be stored a safe distance away from each other.

• Hair spray should be used before inserting the contacts. If hair spray needs to be applied later on in the day then one should keep the eyes closed for some seconds afterwards, until the aerosol has settled.

• Water resistant maskara can contain particles which are most uncomfortable if they happen to get between contacts and eyes. They may also be impossible to be removed from a lens, once they got stuck to it. Make-up powder by definition consists of particles and is therefore advised against.

• Make-up in general contains fat, and fat deposits on contacts prevent water from adhering to them. Hence one should first insert contacts (with fat-free fingers) and then apply make-up. This procedure also prevents one from ruining a make-up in the process of inserting the contacts. There are differing opinions about the right sequence in removing the contacts and un-doing a make-up.

• Some make-up companies also produce cosmetics specially adapted for contact lens carriers.

Tears and Dry Eyes

Tears have more purposes than expressing emotions and raising money for jewelry and fur coats. They protect the eye against evaporation, serve as a lubricant between lid and eye, kill bacteria, transport nutrition and waste products, supply oxygen, and rinse away foreign bodies.

Tears

The tear film consists of three layers:

1. The innermost layer consists of hygroscopic (water attracting) mucus. Without this layer water would not adhere to the eye surface.
2. The medium layer makes up most of the tear film. It contains water, nutritious substances, oxygen, and anti-biotics.
3. The outer layer consists of lipides (ie, fat) which lubricates and protects against evaporation. It is produced by glands sitting on the inside of the eye lids.

Your ophthalmologist should be made aware of any medication (or changes thereof).

Most types of eye drops contain conservational agents which are not intended to stay in the eye for long and may lead to irritations. So the policy should be to either use eye drops or wear contact lenses.

Tear production stops while sleeping. Wearing the wrong type of contact lenses while napping would cut down the oxygen supply and leave waste products in place and is therefore advised against.

Dry Eyes

Dry eyes is a case of insufficient tear production. A variety of factors may cause or contribute to this problem. Some symptoms are stinging, burning or waste products that form a crust at night.

Some reasons for dry eyes are:

• Ageing, climacteric.
• Diseases of the thyroid gland, chronical rheumatism, several dermis diseases.
• Pregnancy and menstrual period.
• Medications, including antihistamines, sleeping and birth control pills, diuretics, adstringent eye drops, cardiovascular medications, pain relievers, anti-inflammatories, beta-blockers, and others.
• Eye strain from reading or computer work, dry or airconditioned environment, dust.
• A wrong diet.

Contact Lenses and Sports

In general, contacts excel at sports, in comparison to eyeglasses. You can enjoy a full field of vision with hardly any risk of injuries. RGPs may pop out in doing exacting sports, therefore soft lenses are more advisable because they sit quite firm in the eye and especially disposables won't be a severe loss if gone away. However, the times of football teams crawling over sports grounds in search of some lost contact lens are long gone. Because of higher oxygen consumption, the most permeable type of contacts should be chosen. And there are a few more restrictions:

Swimming

In a pool, RGPs find water all around them and tend to float away. The lubricating properties of tear fluid are reduced if thinned by water, and exposure to chlorified water is a discomfort in itself.

Soft lenses are likely to well up and suction themselves to the eye, because of different concentrations of salt and minerals within the fluid inside the lens and in the pool water. In (salty) ocean water they may flatten out and also get lost, due to the inverse concentration difference. In the former case, do not use force to extract them from the eye. Instead, wait until they return to their normal shape. A method of speeding things up is to offer them an isotonic environment, which means to rinse the lenses with saline solution.

All in all, it is considered best to go swimming without contact lenses or to use disposables which you throw away afterwards.

Shooting

The hovering behaviour especially of RGPs comes into play again. They take up a fraction of a second to settle down after every eyelid movement, so that marksmen will be annoyed by a change of their keen eyesight.

But an even harder problem is getting dry eyes. Normally people blink with their eyelids every five seconds or so, which keeps the lenses' surfaces moistened. But upon taking aim, marksmen often keep their eyes open for 20 seconds. The tear layer then dries away and the contact lenses become foggy.

Contact Lenses and Work

People working with optical instruments such as microscopes and cameras will enjoy the better handling of these devices without eyeglasses. Some professions require helmets or protection goggles to be worn, which is also easier to do with contact lenses. On the other side there are occupations which have their problems:

Computer People

Right now you are staring fascinated onto the monitor. Your blinking frequency is decreased and the tear layer may already have dried away. And most probably your head is tilted forward so that you have to turn your eyes upward and thereby expose more area of your eyes' bodies to some dry air. Working in airconditioned rooms or under 'clean room' conditions also bears the danger of getting dry eyes.

So what you should do is this: lean back and turn your head up. Eyes get tired faster if exposed to bright illumination, therefore turn down the brightness of your display, check the contrast setting and choose a colour set with a dark background⁵. Get into a habit of focussing some distant object every now and then.

Jobs in Dusty Environments

Construction workers, farmers, bakers and the like are exposed to dust and other tiny particles in the air. Having some of these between contacts and the eye is very disgusting. Some particles like rust even work their way into the material of contacts and cannot be removed without damage. Smoke also consists of particles, as bartenders and waiters can easily tell.

Contact Lenses and Vacations

If all works well at your homeplace then this does not automatically mean that there were no problems abroad or whilst travelling. Long distance flights entail exposure to dry air, therefore some rewetting solution should be at hand. Apart from acquiring jet lag you also run the risk of extending the wearing cycle of your contacts. Using disposables for travelling days can be an option.

Sea and mountain regions are characterized by wind and and dry air, which again brings up the dry eye aspect. Water and snow reflect the sunlight which leads to higher exposure to UV. A set of UV protection sunglasses worn over the contact lenses is therefore recommended. Many people close their eyes while sun-tanning and on long haul flights, and therefore should follow the same regime with their contacts as if going to sleep.

Travelling to tropical regions and deserts means exposure to heat and dust. Heat is no problem for the lenses (you can take them into a sauna if you only remember to blink a lot -- preferrably without annoying other people), but most protein solvents degrade at temperatures above 25°C. Therefore do not keep them in the car or in the sunlight. The refrigerator in a hotel room is a good suggestion for storage.

Irrespective of your destination, the following points apply:

• Take along enough of all the chemistry you rely on because they could be unavailable at your destination.
• Travelling abroad often entails substantial changes to one's metabolism. Montezuma's Revenge and winds are just two reactions, another one is that contacts may develop more protein deposits, as this also depends on the composition of one's diet.
• Hygiene conditions in some countries are completely different from those at home. In all likelihood, the spectrum of bacteria to be found is different, and your cleaning habits are insufficient. Using tap water for washing one's hands may not 'clean' them, and don't even think of rinsing your contacts with it.
• It is a good idea to carry along some backup means, ie, eyeglasses or a package of disposables.

Fun With Contact Lenses - A Beginner's Morning

This is a flow chart of the individual steps which a beginner passes through in a 'worst case' scenario. As you gain professionalism in dealing with contact lenses, more and more items may be deleted, and inserting contact lenses is done without further thinking about it, just like doing one's shoe laces.

1. Wake up and find way to the lenses' storage place without meeting half opened doors or stumbling over sleeping dogs and the like.
2. Identify left lens by colour or imprinted 'L' on appropriate side of container.
3. Wash hands and retrieve lens from disinfection fluid.
4. Use cleansing agent, gently rub lens between thumb and two fingers.
     Optional steps:
   
   • 4a. Walk around flat while rubbing lens.
   • 4b. Curse silently and get down on knees in search of lens within carpet floor.
   • 4c. Be faster than dog or toddler in finding lens.
   • 4d. Use index finger to retrieve lens from toddler's throat.
   • 4e. Return to bathroom and start over from step 4.
5. Rinse lens thorougly before inserting, otherwise encounter very uncomfortable sensations in the eye.
6. Wet lens adheres well to tip of index finger. Use other hand to spread apart upper and lower lid of the eye.
7. Make sure to have left lens properly aligned with left eye.
8. Try to catch eye by surprise: insert lens before blinking.
9. Remove lens from nose or upper eyelid, moisten again.
10. Try to catch eye by surprise: attach lens before blinking.
11. Recover lens from U-turn in plumbing below bathroom sink.
12. Cover bottom of sink with piece of toilet paper.
13. Repeat steps 4 to 10.
14. Inspect nose, eye lids, fingers, and sink in search for lens.
15. Lift upper eyelid and find lens attached to eye, but somewhere on outer rim.
16. Don't panic if lens disappears behind eyeball. Lens will show up again.
17. Use suction device to remove lens from eye. Do not attach suction cup directly to eye.
18. If this starts getting boring, seek advice on endless loops.
19. Repeat steps 4 to 9.
20. Try it the slow way: recall prime numbers greater than 53 while staring into mirror and advancing lens into place.
21. Sigh, praise and thank deity for success.
22. Start over from step 2 with right lens. Avoid stacking lenses on top of each other in same eye.
23. Upon leaving the house, discover blurred and foggy vision due to insufficient cleaning and start over from step 4.
24. Say out loud: it's a matter of training, and capabilities will improve.
25. Set up alarm clock 10 minutes earlier.

26. Find new excuse for arriving late at work.