contact lenses

and Carola Felchner, science journalist

Carola Felchner is a freelance writer in the medical department and a certified training and nutrition advisor. She worked for various specialist magazines and online portals before becoming a freelance journalist in 2015. Before starting her internship, she studied translation and interpreting in Kempten and Munich.

More about the experts All content is checked by medical journalists.

Contact lenses are an invisible visual aid for people with ametropia: the small, round plastic shells are inserted into the eye by those affected, where they float on a tear film in front of the cornea. Read here what types of contact lenses there are, what advantages they offer and what you need to consider when using contact lenses.

What are contact lenses?

Contact lenses are round plastic shells that are used as visual aids for patients with ametropia. They sit directly in the eye (more precisely: they swim on a thin film of tears). This means that contact lenses are less noticeable than glasses, but the principle of operation is the same:

Contact lenses change the refraction of light, which is either too weak or too strong in the case of ametropia, and thus enable sharp vision. They are therefore an alternative to glasses and laser eye correction.

Types of contact lenses

Contact lenses can be classified according to various criteria. With regard to dimensional stability, a distinction is made between:

• soft contact lenses, e.g. made of silicone hydrogels
• hard contact lenses (or dimensionally stable contact lenses), e.g. made of silicone polymers

According to the number of corrected distances there are:

• Monofocal lenses (single vision lenses): They can only be sucked at a distance for sharp vision (e.g. in the distance).
• Bifocal and multifocal contact lenses (multifocal lenses): You can correct the vision at two (bifocal) or more (multifocal) distances.

Contact lenses can also differ in their shelf life. There are daily, monthly and annual lenses.

In addition, some special lenses are available, such as Ortho-K contact lenses (for correcting the shape of the cornea) and toric contact lenses (with differently shaped curvatures to compensate for astigmatism). There are also non-medical lenses that are mostly used for fun.

The therapeutic contact lenses represent a special form of application. The ophthalmologist uses them to apply a drug or as a kind of bandage for superficial corneal injuries.

Hard and soft contact lenses

Hard and soft contact lenses have different advantages and disadvantages due to their material:

Hard contact lenses

The first hard contact lenses, which were developed from the 1950s, consisted of oxygen-impermeable Plexiglas. Nowadays the only hard lenses used are dimensionally stable contact lenses made of a somewhat softer material, which have a high permeability for oxygen. They are only eight to ten millimeters in diameter, so they only cover part of the cornea. When you blink, they slide on the eye, so that the tear film in the eye is continuously renewed and fresh oxygen comes to the eye. This reduces the risk of infection.

With careful care, these hard contact lenses are extremely durable and can sometimes also be used as annual contact lenses. Due to their low flexibility, they are also suitable for correcting mild to moderate astigmatism.

The disadvantage of hard contact lenses is that they often create a foreign body sensation in the eye initially. Usually, however, those affected quickly get used to the invisible visual aid.

Soft contact lenses

Soft contact lenses are about 13 to 14.5 millimeters in diameter. They consist of hydrogels or silicone hydrogels and thus approximately 40 to 80 percent water. The higher the water content, the more permeable these contact lenses are for oxygen.

Because of their flexibility, soft contact lenses adapt well to the shape of the wearer's cornea. This increases the wearing comfort and is the reason why they are usually well tolerated straight away, even when they are worn for the first time.

The disadvantage of soft lenses is that they tend to dry out if the eye cannot maintain the water content (e.g. with dry heating air) and thus increase the risk of infections.

Daily, monthly and annual lenses

Contact lenses that are only used for one day and then end up in the trash are called daily contact lenses. Usually these are soft contact lenses. They are particularly practical because there is no need to clean or store them. Daily lenses are therefore well suited for people who only wear contact lenses now and then, for example when traveling or doing sports. However, the costs for these lenses are usually higher than for monthly or annual contact lenses that can be used over a longer period of time. However, these two contact lens variants require regular care.

Bifocal and multifocal contact lenses

In contrast to monofocal lenses, they can correct the view at more than one distance:

Bifocal contact lenses

They have two diopter areas that are separate from one another: In the lower half there is an area for near vision. If you look through this part of the bifocal contact lens, you can see objects that are close by. On the other hand, if you look through the upper half of the contact lens, you have a clear picture of objects further away.

A disadvantage of this type of lens is that it hardly covers any intermediate areas, if at all.

Multifocal contact lenses

These multifocal lenses have more than two diopter ranges ground in so that objects can be seen sharply at different distances. The transitions between the different diopter areas are usually stepless - these varifocal contact lenses work like varifocals. These lenses are available as daily, monthly and annual lenses.

Special contact lenses

Permanent lenses

You usually have to take your contact lenses out of your eyes overnight. Otherwise there is a risk that they will dry out and form deposits that can lead to infections of the eye. However, there are also special day-and-night contact lenses (permanent lenses) made of particularly oxygen-permeable material that can remain in the eye while sleeping. They are therefore well suited for all situations in which it is not possible to clean or change the contact lenses regularly, for example on vacation or on long-haul flights.

However, some ophthalmologists are critical of the use of permanent lenses. These contact lenses can cause problems for easily dry and irritated eyes. People with sensitive eyes can also find it uncomfortable to have a foreign body in their eye around the clock.

Ortho-K lenses

So-called Ortho-K lenses (orthokeratological contact lenses), also known as night lenses, are only used at night. You should model the cornea while you sleep so that you can see clearly during the day without visual aid. However, this only works with some forms of ametropia and then only with consistent use. Often the eyesight deteriorates again during the day.

Toric contact lenses

Patients with nearsightedness or farsightedness can use conventional contact lenses with an even curvature (spherical contact lenses). However, if there is a particularly severe curvature of the cornea, the ophthalmologist will prescribe special ring-shaped contact lenses (toric): Curvature of the cornea means that the refraction of the eye behaves differently in the horizontal plane than in the vertical plane. Toric contact lenses compensate for the different refractive powers through their "donut shape". They are available as dimensionally stable or soft versions, as well as toric monthly lenses or daily lenses.

Toric contact lenses must be carefully adjusted to fit properly on the eye.

Non-medical contact lenses

There are also contact lenses that are not worn for medical reasons, but for other purposes. These include, for example, colored or UV contact lenses. While the natural eye color can be changed with colored lenses, UV contact lenses have a glowing effect under black light. Both variants are mainly used for cosmetic purposes, for example to give the carnival or disco outfit the finishing touch.

Usually these types of lenses do not change the refractive power of the eye and therefore do not correct ametropia. People with ametropia who want to wear such pure "fun lenses" must also put on glasses in order to see clearly.

When do I need contact lenses?

Contact lenses are usually necessary when someone has ametropia and cannot or does not want to wear glasses to correct their vision. They are suitable for people with the following ametropia:

• Astigmatism
• myopia
• Farsightedness
• Presbyopia

Of course, contact lenses do not offer a cure for ametropia. As with glasses, it is merely a visual aid.

The therapeutic contact lenses represent a special form. The ophthalmologist uses them to apply medication or as a kind of bandage for superficial corneal injuries.

However, contact lenses are not suitable for all patients in everyday life. In a dusty environment or when handling certain chemicals, for example at the workplace, there is a risk that foreign bodies can get between the lens and the cornea and cause injuries. Before fitting contact lenses, the ophthalmologist should ask the patient about their daily habits in order to assess whether they can use the lenses without restrictions.

Glasses or contact lenses?

When it comes to the question of whether contact lenses or glasses are the better choice, everyone has to decide for themselves. Many ametropia people also opt for a combination of both. When deciding on your own "main visual aid", you should first clarify the advantages and disadvantages of contact lenses compared to glasses:

• Less conspicuous: Contact lenses are less noticeable than glasses. That is why many people choose contact lenses as an alternative to glasses for aesthetic reasons, among other things.
• All-round vision: Contact lenses allow all-round vision and do not restrict the wearer's field of vision - as glasses do with their frames.
• suitable for water rats: contact lenses can also be used for water sports. There is no need for swimming goggles with vision correction. Splashes that can be deposited on the lens do not block the clear view and, unlike glasses, contact lenses cannot fog up.
• No fogging: In contrast to glasses, contact lenses cannot fog up.
• Additional costs: For contact lenses (except for daily lenses) there are additional costs for care products.
• (Initial) fiddling: Inserting and removing the lenses can - at least initially - be a lot of fiddling. Putting on and taking off glasses is much easier and quicker.
• Possible source of irritation: Contact lenses sit directly in the eye and stress it accordingly, which is why they should only be used by people with good eye health.
• Limited wearing time: Depending on the contact lenses used, the oxygen supply to the eye may be reduced so that the lenses should only remain in the eye for a limited time per day.

When deciding which visual aid is more suitable in each individual case, your own preferences, tolerances and main areas of application also play a role.

For example, if someone often works in dusty environments or with chemicals, glasses are probably a better solution. In the case of contact lenses, the risk of foreign bodies getting between the contact lens and the cornea and causing injuries would be very high in such cases.

Even those who sit in front of the computer for many hours every day may be better off with glasses. When staring at the monitor for a long time, you blink less often, which can quickly dry out your eyes or contact lenses. Headaches, feelings of pressure in the eyes and blurred vision are also possible effects here, which are summarized under the term "Computer Vision Syndrome" (CVS) and, according to studies, are more likely to occur in people with contact lenses than in people who wear glasses.

Discuss with your ophthalmologist which visual aid - glasses or contact lenses - is best for your needs.

What do you do with a contact lens fitting?

If this is your first time having contact lenses fitted, your ophthalmologist should check beforehand whether your eyes are healthy or whether there is an infection, for example. If the findings are normal, he will discuss the advantages and disadvantages, the costs, but also the individual benefits of the different types of contact lenses with you: For example, if you have astigmatism, you need toric lenses.

Usually the ophthalmologist has a set of so-called trial lenses of the various contact lens types in stock. As a rule, these are individual lenses that you can use once for the adjustment. In this way you can assess how comfortable the various contact lenses are.

When you go to the ophthalmologist, you will then have to try it to show whether you can tolerate the lenses. With hard contact lenses it takes about half an hour, with soft contact lenses it takes one to two hours. Make sure that the contact lens moves evenly up and down when you blink and that there is good tear fluid under it. In addition, it should not stick out and fall out easily, nor should it stick too tightly to the cornea.

What are the risks of contact lenses?

Most complications for contact lens wearers result from poor handling hygiene: Improper cleaning of the contact lenses can lead to infections caused by bacteria or fungi. As a result, corneal inflammation or conjunctivitis can develop, which can damage the eye or become chronic. The latter usually makes it impossible to continue wearing contact lenses. However, if detected in time, most eye infections can be treated well.

If there are any signs of an eye infection (such as unusually reddened, sore eyes), remove the contact lenses immediately and see an ophthalmologist.

There are seldom allergic reactions to the contact lens material or to the lens cleaning agents. In this case, it is worth consulting an ophthalmologist. It may be better for you to switch to a different lens material or to glasses as an alternative.

Contact lenses: dry eyes as a risk factor

Many contact lens wearers are familiar with the feeling of dry eyes - caused, for example, by dry air (e.g. in heated or air-conditioned rooms), working long hours at the PC or taking certain medications such as beta blockers or some antidepressants. If the contact lens no longer floats on sufficient tear fluid, this can mechanically irritate the eye.

If you often struggle with this problem, you can buy special contact lenses for dry eyes (e.g.made of silicone hydrogel), which are now offered by various manufacturers.

What do I have to consider with contact lenses?

At first, it may feel unfamiliar to wear contact lenses. However, most people get used to the new feeling within a few hours or days. The habituation effect sets in quickly, especially with soft contact lenses, so that the small visual aids are no longer perceived as annoying.

Due to the so-called adhesive forces, the contact lenses adhere well to the eye. So, under normal circumstances, you don't have to worry about losing your contact lenses.

Where can I get new contact lenses from?

After the first adjustment, you can easily order your contact lenses on the Internet or purchase them from an optician or drug store. If you are unsure about the quality, you can get trial lenses from many manufacturers. If you have received some from the ophthalmologist or optician with whom you get on well, it is best to stick with this model.

There are a few parameters you must pay attention to when ordering contact lenses (online). Use the information on your current contact lens packaging or the prescription as a guide:

• Cylinder (CYL) and axis (AX)
• Diameter (DIA)
• Base curve / radius (BC)

The value of the cylinder indicates a possible astigmatism. The axis describes the measured line of the refractive error of your eyes. The diameter indicates the size of the contact lens. The base curve (BC) is the value that indicates the curvature of the lenses. It is important that you always wear contact lenses with the base curve prescribed for you. Otherwise the lenses can fall out more easily or stick too tightly to the eye.

How do I clean my contact lenses properly?

To prevent germs from depositing on the contact lenses and causing eye infections, there are a few basic principles of hygiene that you should follow.

• You should only put cleaned contact lenses in your eyes. It is best to always do the cleaning immediately after removing the lenses. Then they are already prepared for the next assignment.
• To clean the lenses, simply place them in your washed, lint-free dried hand. Then put a few drops of a cleaning solution suitable for your lens type on the lenses and rub them in for about twenty seconds. How to remove dirt particles and fat deposits.
• Then rinse the contact lenses with saline or cleaning solution and then put them in the storage container (see below).
• Before inserting them, you can rinse the contact lenses again with saline solution to remove any residues of the cleaning or disinfecting solution.

Never use tap water or spit to clean the contact lenses, as they contain germs. Also note that you should only use hygiene solutions that are suitable for your type of contact lens. For example, soft contact lenses can be damaged by treatment with a hard contact lens solution and vice versa.

The tear film contains proteins that are also deposited on the lens surface. This makes them less permeable to oxygen and therefore less tolerable. This is why you should treat your lenses with a special protein remover about once a week.

You should also disinfect the storage container for the contact lenses at regular intervals to kill bacteria, fungi or viruses. You can purchase suitable solutions in the pharmacy or drugstore. It is advisable to replace the container after one to three months.

How long can I wear the contact lenses?

The different types of lenses have different wearing times. Your eye doctor will explain how long you can wear your custom contact lenses. In general:

For the first few weeks after fitting, it is recommended that you only wear the contact lenses a few hours a day and use glasses for the rest of the day. Then gradually increase the daily wearing time of the contact lenses. This will allow your eyes to slowly get used to the foreign body.

If you notice pain, visual disturbances or eye redness while wearing the contact lenses, you should remove the lenses and contact your ophthalmologist. He can find out where the discomfort is coming from and decide how to fix it.

What should I do if I lose my eye contact lens?

It is a myth that contact lenses can slip behind the eye and get lost there, because the anatomical conditions make it impossible. At most it can happen that the contact lens folds up under the eyelid, for example by rubbing the eyes vigorously. In this case, simply slide the upper or lower eyelid up as far as possible and grasp the unfolded contact lens with two fingers.

If you have trouble locating the lens, you can use eye drops to moisten your eye. This makes it easier for the contact lens to slide on the cornea. If none of these help, see your ophthalmologist. This will then help you remove the lost contact lens.

General information for everyday life

If you plan to use eye drops to moisturize your eyes, they shouldn't contain preservatives. In particular, these can become embedded in the soft lenses and thus destroy them. Ask your ophthalmologist which eye drops you can safely use.

Visits to the sauna, steam bath or solarium are permitted with contact lenses. The best way to swim and dive is with flexible contact lenses. For hygienic reasons, however, it makes sense to wear swimming goggles or diving goggles. After swimming, you must remove and clean your contact lenses to remove any germs or chemicals that may have been found in the pool water. This prevents eye infections and irritations.

Tags:  alcohol sports fitness sleep