Contact lens

Contact lenses ( also adhesive lenses, adhesion shells or contact glasses, not to be confused with contact lenses ), optical aids, among the visual aids and as such an alternative to glasses dar. contact lenses are not directly on the cornea of the eye, but float on a fine tear film. We distinguish between rigid (hard) and soft contact lenses. They can be corrected most optical refractive errors ( ametropia ) such as nearsightedness, farsightedness, astigmatism or presbyopia. Particularly complex forms of visual disorders such as keratoconus, Keratoglobus or very different refractive conditions ( anisometropia ) can be corrected with contact lenses well, usually better than with glasses. The statutory health insurance in Germany carry only in certain cases, the cost of this form of visual aids.

• 3.1 contact lenses for the correction of nearsightedness or farsightedness
• 3.2 Toric Contact Lenses
• 3.3 contact lenses for the correction of presbyopia 3.3.1 shaped segment bifocal lenses
• 3.3.2 Concentric multifocal
• 3.3.3 monovision technique

• 7.1 sauna
• 7.2 Swimming
• 7.3 Scuba Diving
• 7.4 Occupations
• 7.5 pregnancy

History

The oldest idea of ​​a modification of the refractive properties of the eye by an intervention directly on the cornea can be at Leonardo da Vinci prove in a paper from 1508, which proposed an immersion of the eye in a water-filled glass jar. René Descartes had in 1636 the idea of ​​a liquid-filled glass tube that is set for the correction of refractive error directly to the eye. John Herschel in 1823 described a " with animal jelly -filled spherical capsule that is applied to the surface of the eye" and thus came to today's contact lenses now near.

In the 1880s, at least two inventors worked to first implement the concept of the contact lens into reality: Adolf Eugen Fick and August Müller independently developed glass bowls that covered most of the ocular surface. August Müller himself, who was nearsighted, could wear this type of lenses only for a maximum of half an hour. The optician fine William Bloom in 1936 the first plastic PMMA as a contact lens material instead of glass one. Already in the 1930s experimented Heinrich Wöhlk in Kiel with scleral lenses made ​​of Plexiglas. He succeeded first scheduling to produce today's modern form of long portable contact lens. He used a method for precise cast of the cornea of ​​the eye, which allowed only the production of a custom -fit contact lens. Wöhlk can thus be regarded as the inventor of the modern hard contact lens. In fact, he lacked capital and so he could not apply for a patent his invention. 1948, the first lens made ​​entirely of PMMA was patented by Kevin Tuohy, which only covered the cornea and not the entire sclera. Another important breakthrough came in 1959 Otto Wichterle, who invented the hydrogel HEMA for the production of soft contact lenses. The so-called Wichterle lenses were still fragile and sensitive in use. In the following years, Jacqueline Urbach developed a much thinner, far more stable material for soft lenses, which was patented in 1974 ( Hydrophilic Contact Lens Material; patent number 3'985'697 ). In 1975, she turned in Amsterdam, the first mass-produced in Europe soft lenses under the name " Urosoft " before and received in 1977 by the FDA in the United States, the authorization to drive one of the first soft lenses at all.

Lens types

RGP ( rigid )

In 1976, the first oxygen- permeable rigid contact lenses came on the market. Today's often abbreviated as rigid gas permeable RGP for. The diameter is usually between eight and ten millimeters. They swim movable on a tear film. Further development of the present resins have rigid contact lenses oxygen permeabilities in the range of 30 to 100 Dk. A large part of oxygen transport to the cornea passes through the lens material through such. A slight astigmatism can be compensated by the shape stability in combination with the underlying lens tear film. Optimized measurement methods and better shaping of the contact lenses and comfortable materials could improve tolerability compared to the first GP lenses. Aging processes can deform the lens and damage the cornea. When changing the contact lenses with a lens suction minor injuries and their subsequent infections can be triggered when too much pressure on the cornea.

Soft contact lenses

Soft contact lenses are flexible and conform to the shape of the cornea. The diameter is typically 12 to 16 mm, therefore, the lens edge is located at the eye is opened, under the eyelid. The wearing time of soft contact lenses varies from daily, over 14 day and month up to years lenses.

Hydrogel lenses

Hydrogel composed of a hydrophilic polymer and water, depending on the lens in a mass ratio of about 1:1. Such polymers are, for example Ocufilcon or Omafilcon, a number of other, similar products are approved by the FDA. The polymer of these contact lenses is not permeable to oxygen. The oxygen transport takes place rather by diffusion through the water contained in the lens. Therefore, the oxygen permeability of contact lenses is generally higher, the greater the proportion of water is. In this way, oxygen permeabilities of up to 30 Dk can be achieved.

Silicone hydrogel lenses

For multi-day continuous wear higher oxygen permeabilities are needed to prevent corneal swelling (especially overnight). For this reason, the first lens was introduced in 1999 from a so-called silicone hydrogel ( Balafilcon ), which can be worn continuously up to a month. It is the blend of a hydrophilic polymer oxygen-impermeable, a hydrophobic highly oxygen permeable silicone polymer, and water. The silicone polymers oxygen permeability values ​​can be achieved of well over 100 Dk.

However, the hydrophobic surface of these materials has the disadvantage that the lens surface is less wettable track of what needs to be partially offset by additional surface treatments. A further drawback that must be taken for the higher oxygen permeability into account, the higher stiffness of silicone hydrogel lenses compared to hydrogel. This can occur under certain circumstances easier mechanical irritation of the eye. The contact lens manufacturers are constantly working on new materials to reduce these problems. As silicone hydrogels have become available which have a relatively good wettability, even without surface treatment (eg Comfilcon ).

Hybrid contact lenses

To combine the advantages of dimensionally stable contact lenses and the comfort of soft contact lenses, so-called hybrid lenses have been developed since 2001, which are now offered by some manufacturers. They have the oxygen permeable core of a dimensionally stable contact lens and a soft coating. 2005, they were approved for the American market. Specifically, patients suffering from keratoconus and rigid contact lenses previously required, so can benefit from the wearing comfort of a soft contact lens.

RGP contact lenses compared to soft contact lenses

The choice between RGP ( rigid gas permeable, rigid oxygen permeable ) or soft contact lenses depends on the habits of the wearer, but also can be affected by medical aspects (some astigmatism can be better corrected by rigid lenses). Rigid contact lenses have the advantage of not being able to dry out. Another aspect is the frequency of wearing: Occasional Wear, such as during sporting activities, the soft contact lenses are cheaper in general. When wearing daily contact lenses have inherently stable despite the higher purchase and adjustment costs have a cost advantage, since they have to be replaced less often with good care. The eyesight of the wearer changes relatively quickly, such as at a young age, it may be more appropriate to use soft contact lenses, in order not to buy more often the relatively expensive GP lenses have. In windy or dusty environment consists in rigid contact lenses is the risk that access to pain leading foreign bodies under a rigid contact lens. Due to the almost direct adhesion of soft contact lenses on the ocular surface and its extension to below the lid margin soft contact lenses sit firmly in the eye as dimensionally stable, which also reduces the risk of loss. The risk of infections of the cornea is soft contact lenses is greater than GP lenses ( 3.5 vs 1.1 cases per 10,000 support ).

The settling time of rigid contact lenses is longer than that of soft. While soft contact lenses are usually perceived already with the first insertion only to a small extent as a foreign body in the eye, rigid contact lenses require a period of familiarization of three to six weeks. Then at GP lenses continuous wear is required in order not to lose the habituation effect. Many carriers feel but even after this period of familiarization with GP lenses a stronger foreign body sensation than with soft contact lenses.

Lens functions

Contact lenses for the correction of nearsightedness or farsightedness

The common contact lenses are used for correction of nearsightedness or farsightedness. This spherical lens shapes, aspheric lens shapes or forms spherical lens be used with aspheric periphery.

Toric Contact Lenses

With toric contact lenses astigmatism (astigmatism ) is corrected. Next to the diopter value, the values ​​for the astigmatism and the cylinder axis have to be considered in manufacturing. The astigmatism is compensated by cylindrical parameters. The lens has to sit in a defined position. This is achieved by various methods that require careful adjustment.

Contact lenses for the correction of presbyopia

In the fourth decade of life, the human eye gradually loses the ability to focus on close distances. This phenomenon is called presbyopia or presbyopia. In rare cases, it may be necessary due to pathological changes or injuries to the eye previously a near correction. Unlike traditional contact lenses, which are only seeing in the distance or proximity can be corrected, since 1982 multifocal lenses offer the possibility of distinct vision at different distances. Multifocal lenses are divided into segmental bifocal or multifocal concentric. A special form is monovision technique dar. Which type of lens is used, depending on the physiological conditions and the type of application. Multifocal lenses can be manufactured both as a rigid contact lenses as well as soft contact lenses.

Shaped segment bifocal lenses

This manufacturing principle is also referred to as alternating ( alternating ) system is generally made ​​up of two sector-shaped zones of different optical effects. When looking into the distance the eye looks through the top - correcting for the distance - optical zone. When looking into the close, the eye is turned down, the contact lens is, however, pushed by the influence of the lower lid up and you can see through the near zone.

Concentric multifocal

In this type of lens two or more annular vision zones are arranged concentrically. In modern contact lenses the areas now go seamlessly into each other. The user can simultaneously use different optical zones, hence the additional designation as " simultaneous system ". The foundations have already been described in the 1950s by Collins and de Carle. The eye is at the same time the image of the distant and nearby offered, and it chooses (unconsciously ) the desired image.

Monovision technique

Here no multifocal contact lenses are used to correct presbyopia, but it resembles an eye for distance from the other eye for near vision. Using this technique, however, there are some limitations for binocular stereoscopic vision.

Night lenses

Another form of contact lenses are lenses orthokeratologische night. These are used before sleep and left overnight in the eyes. During the gestation period to correct the shape of the cornea of the eye. This deformation is not permanent, but it remains for a period of one to three days to receive, in the sharp vision without corrective lenses is possible.

Association of lenses

Association of lenses are used by the ophthalmologist in case of injuries of the cornea and can remain for up to four weeks.

Cosmetic Contact Lenses

Colored or painted contact lenses ( also called motif lenses ) are used mainly for aesthetic or cosmetic purposes. A medical indication for colored contact lenses ( iris lenses) is available in light sensitivity. Their optical functions are lower than that of conventional lenses. They are available in all standard colors and motifs, such as reptile or manganese motifs that win to Mardi Gras, Halloween and theme parties increasingly popular. The version " sclera - Lens" ( German " full cup contact lens " ) can cover the whole eye. Such contact lenses may be worn up to six hours according to the manufacturer using eye drops and are not in Germany for private sale. Due to their size the insertion of a full cup contact lens is more difficult than a normal soft contact lens.

Correction characteristics in comparison to glasses

Contact lenses for the correction of myopia are physical reasons thicker at the edge than in the center, and therefore at high levels getting used to as such for the correction of hyperopia, which are thinner toward the edge. In high myopia, however, contact lenses offer the advantage that what is seen due to the direct seat on the eye, unlike a pair of glasses is not reduced. Thereby is obtained a contact lens generally has a better correction of the refractive error. In return, the seen so the field does not grow at severe farsightedness, compared with a normal vision is not reduced. In all cases, the restriction of the visual field through the spectacle rim can be omitted and the eyes follow the natural movement patterns. Contact lenses often have a slight tint, to facilitate handling.

Customization and maintenance

Contact lenses are not good and properly adjusted can damage the eye. Therefore, the adaptation ( contactology ) should be performed by an appropriately trained specialist, typically by an ophthalmologist, an optician or optometrist. This assures the best possible result and is liable in case of problems in legal prescribed framework. The fitter takes account of the individual shape of the eye as well as the force of the eyelids wink. Special attention is paid to the tear film whose properties co-determine the respective lens material.

Also on the wearing time of contact lenses to look for. Daily lenses represent a special case because they are used only for specific situations ( sports, work, if not for safety glasses can be worn etc.). The Daily lenses are removed and disposed of after a few hours, but no later than twelve hours from the eye. Soft contact lenses should be replaced regularly. Manufacturers offer the customer several options to choose from. Here are periods of one to two weeks possible up to twelve months. The aging of the contact lenses reduces the wearing comfort. The most common mistake is to use too long wearing time of replacement lenses. At the end of its useful life, the eye is significantly worse supplied with nutrients, making the risks mentioned below arise. Therefore, the duration of wearing the contact lenses should always be done in consultation with the ophthalmologist and optician.

The contact lens wearer should regularly carry out the Nachkontrolltermine to avoid risks. Practice good hygiene must be taken by the contact lens care products selected to match the lens material and the fluids are changed regularly. Age contact lenses and can then have signs of wear, deposits and damage.

Risks and side effects

The main side effects of contact lenses are hyperemia in the conjunctiva or limbus, neovascularization, and conjunctivitis, keratoconjunctivitis sicca, and especially Riesenpapillenkonjunktivitis.

The probability of conjunctivitis can be reduced by compliance with hygiene regulations when handling contact lenses. The risk of all these side effects generally increases with the wear time. Since chlorine may affect the function of contact lenses while swimming, the use of daily lenses or goggles is recommended.

Limitations when wearing

Sauna

Due to the dry air and the regular Saunaaufguss the eyes can be irritated. Furthermore, deposits form on the lens. It is therefore advisable to use for sauna visits contact lenses that are highly permeable to oxygen, which is expressed in many online stores on the " DK value ".

Swimming

Contact lenses are often lost during the swim. In GP lenses is more likely than with soft contact lenses because soft lenses more laid eyes on the cornea. The material of the contact lenses can be deformed by chlorine and salt water, which would be detrimental to the eye.

Skin diving

The use of soft daily lenses is recommended. If you lose the lenses of the financial loss is small as opposed to monthly or annual lenses or, in particular diving masks with optical lenses. Also, daily lenses usually total well over a longer period significantly cheaper than, for example diving masks with optical lenses. If after a long period of time, a change in the optical properties of the eye has occurred, no new (expensive) dive mask is required, but there are only new daily lenses to procure with the changed diopter values ​​, the elapsed dive mask without correction can still be used.

Soft lenses are days currently ( August 2012) in stores at prices starting at about 40 cents per piece available. The results for 10 dives on different days at a price of about 8 euros.

The high water pressure, if rapid emergence in GP lenses lead to a poor term as collect from the cornea emerging air bubbles under the lens. From a medical point of view but this is not a handpump in the Diving with soft contact lenses have been observed any negative or harmful effects.

The rapid emergence but should be for health reasons generally avoided as it involves substantial risks.

Occupations

In most professions is wearing contact lenses no disadvantages compared to a pair of glasses dar. In rooms with low humidity or air conditioning systems, the use of contact lenses designed overall problematic because it can quickly lead to dry eyes and thus irritation of the cornea. What professions can eventually lead to problems when wearing contact lenses should be examined in the discussion at the ophthalmologist or optometrist.

Pregnancy

Due to hormonal changes during pregnancy, the amount of tear fluid can reduce and thus lead to dry eyes. During delivery of the internal pressure of the eye and increases the flow of tears increases. Thus, the wearing of contact lenses during labor can be quickly unpleasant.

Manufacturer

• Johnson & Johnson Vision Care
• Cooper Vision
• Alcon (Ciba Vision)
• Sauflon