Contact lens

from Wikipedia, the free encyclopedia

Contact lenses (also sticky lenses , sticky cups or sticky glasses ; not to be confused with contact glasses ) are optical aids, belong to the visual aids and as such represent an alternative to glasses . Contact lenses do not lie directly on the cornea of the eye , but rather float on a thin film of tears . A distinction is made between dimensionally stable (hard) and soft contact lenses. They can be used to correct most optical ametropia such as nearsightedness , farsightedness , astigmatism or presbyopia . Particularly complicated forms of ametropia such as keratoconus , keratoglobus or very different refractive ratios ( anisometropia ) can be corrected well with contact lenses, usually better than with glasses. The statutory health insurance companies in Germany only bear the costs for this form of vision aids in certain cases.

Contact lens for correcting myopia
A lens aspirator can make it easier to remove the contact lens

history

Adolf Eugen Fick
Size comparison of contact lenses from the 1950s to current dimensionally stable lenses

The oldest idea of ​​a modification of the refractive properties of the eye by means of an intervention directly on the cornea can be demonstrated by Leonardo da Vinci in a paper from 1508, who suggested immersing the eye in a water-filled glass vessel. In 1636, René Descartes had the idea of ​​a glass tube filled with liquid that is placed directly on the eye to correct ametropia. In 1823 John Herschel described a "spherical capsule filled with animal gel that is applied to the surface of the eye" and thus came close to today's contact lenses.

In the 1880s, at least two inventors worked on turning the concept of the contact lens into reality for the first time: Adolf Eugen Fick and August Müller independently developed glass bowls that covered most of the surface of the eye. August Müller himself, who was very near-sighted, could only wear this type of lens for a maximum of half an hour. In 1936, the optician William Feinbloom first introduced the plastic PMMA as a contact lens material instead of glass. Heinrich Wöhlk was already experimenting with scleral shells made of Plexiglas in Kiel in the 1930s . He was the first to succeed in producing today's modern form of the long wearable contact lens. He used a process for the precise casting of the cornea of ​​the eye, which made it possible to manufacture an individually tailored contact lens. Wöhlk can therefore be considered the inventor of the modern hard contact lens. In fact, however, he lacked the capital and so he could not apply for a patent for his invention.

In 1948 Kevin Tuohy applied for a patent for the first lens made entirely from PMMA, which only covered the cornea and no longer the entire sclera . Another important breakthrough came in 1959 by Otto Wichterle , who invented the HEMA hydrogel for the manufacture of soft contact lenses. The so-called Wichterle lenses were still easily breakable and sensitive to use. In the following years, Jacqueline Urbach developed a much thinner, far more stable material for soft lenses, which was patented in 1974 (Hydrophilic Contactlens Material; patent number 3,985,697). In 1975, in Amsterdam, she presented the first mass-produced soft lenses in Europe under the name "Urosoft" and in 1977 received approval from the FDA in the USA to sell one of the first soft lenses ever.

properties

Wettability

In addition to oxygen permeability, the wettability of the contact lens surface is a key material property for the physiological compatibility of contact lenses. A wettable contact lens surface enables the contact lens to be integrated into the tear film and thus the contact lens to slide in the tear film on the cornea . Furthermore, good and uniform wetting is a prerequisite for good optical imaging in the eye. For this, the contact lens surface has to be hydrophilic, ie it has to contain polar groups of molecules. The wettability of a material can be measured in vitro using the contact angle . These surface properties are worsened if an oil film is deposited on the lens (if the meibomian oil glands of the eyelids are overactive, if there are fatty vapors when cooking or deep-frying, due to leftover makeup, etc.).

Lens types

The materials for contact lenses are macromolecular organic materials (polymers), they belong to the class of plastics (plastics). The polymers are roughly divided into block polymers (monomer sequence: AAABBB), alternating polymers (monomer sequence: ABAB) and statistical polymers (monomer sequence: AABABB).

RGP contact lenses (dimensionally stable)

Dimensionally stable contact lens

In 1976 the first oxygen-permeable, dimensionally stable contact lenses came onto the market. Today it is often abbreviated to RGP for rigid gas permeable . The diameter is usually between eight and ten millimeters. They swim flexibly on a tear film. Due to the further development of plastics, today's dimensionally stable contact lenses have oxygen permeability with Dk values ​​of 140 and more. A large part of the oxygen transport to the cornea thus runs through the lens material. A slight astigmatism can be compensated by the dimensional stability in connection with the tear film lying under the lens. Optimized measuring methods and more favorable design of the contact lenses as well as more comfortable materials have improved the compatibility with the first dimensionally stable contact lenses. Aging processes can deform the lens and damage the cornea . When changing contact lenses with a lens suction device, too much pressure on the cornea can cause minor injuries and, as a result, infections.

materials

Hard contact lens materials are generally polymers containing methyl methacrylate to improve mechanical stability and optical properties as well as siloxane and, in most cases, fluorine compounds, both of which increase the oxygen permeability of the material.

By splitting the C = C double bonds in the methacrylic acid residue of the various methacrylic acid esters, the backbone-forming chain is created, to which the residue groups are attached. This arrangement can be compared to a packed clothesline.

Soft contact lenses

Soft contact lenses
Section through a soft contact lens (−6.5 D)
Dried out soft contact lenses

Soft contact lenses are flexible and adapt to the shape of the cornea . The diameter is usually between 12 and 16 mm, so the edge of the lens is below the edge of the eyelid when the eye is open. The wearing time of soft contact lenses varies from daily, over 14 daily and monthly to yearly lenses.

Hydrogel lenses

With the exception of pure silicone contact lenses, soft contact lenses are now hydrogels, ie contact lenses that absorb water. Hydrogel contact lenses are often block polymers because hydrophilic and hydrophobic materials (e.g. MMA / NVP ) are mixed. They contain water in a mass ratio of about 1: 1. Such polymers are e.g. B. Ocufilcon or Omafilcon, a number of other, similar materials are approved by the FDA . The polymer in these contact lenses is not permeable to oxygen. Rather, oxygen is transported by diffusion through the water contained in the lens. Therefore, the oxygen permeability of these contact lenses is generally higher, the greater the water content. In this way, oxygen permeability of up to 30 Dk can be achieved.

materials

Depending on the monomers used, HEMA homopolymers, HEMA copolymers, HEMA-free copolymers or silicone hydrogels are formed during the polymerization . HEMA copolymers are essentially created by adding vinyl pyrrolidone (NVP) with or without methacrylic acid (e.g. in HEMA / NVP), glycerol methacrylate (e.g. in HEMA / GMA polymers), dimethylacrylamide (e.g. in HEMA / DMA polymers) or phospharylcholine (e.g. in HEMA / PC polymers). HEMA-free copolymers are mainly formed from the copolymerization of methyl methacrylate and vinyl pyrrolidone with or without the addition of dimethylacrylamide (MMA / NVP).

As with the materials for hard contact lenses, long polymer chains are created in which the individual monomers are bound to one another in a more or less random order. The challenge in the production of hydrogel materials is to restrict the block formation of hydrophilic components with one another and hydrophobic components with one another to the lowest possible level through thorough mixing.

By mixing different monomers, the material properties can e.g. B. in terms of water content and thus the oxygen permeability can be controlled and optimized.

Silicone hydrogel lenses

For several days of uninterrupted wear, higher oxygen permeability is necessary to prevent swelling of the cornea (especially overnight). For this reason, the first lens made of a so-called silicone hydrogel (balafilcon) was introduced in 1999, which can be worn continuously for up to a month. This is a mixture of a hydrophilic, oxygen-impermeable polymer, a hydrophobic, highly oxygen-permeable silicone polymer, and water. Oxygen permeability values ​​of well over 100 Dk can be achieved through the silicone polymers.

However, the hydrophobic surface of these materials has the disadvantage that the lens surface in the eye is more difficult to wet, which has to be compensated in part by additional surface treatments. Another disadvantage that has to be accepted for the higher oxygen permeability is the higher rigidity of silicone hydrogel lenses compared to hydrogel lenses. This may cause mechanical irritation of the eye more easily. The contact lens manufacturers are constantly working on new materials to reduce the problems mentioned. Silicone hydrogels are now available that have relatively good wettability even without surface treatment (e.g. Comfilcon).

Hybrid contact lenses

In order to combine the advantages of dimensionally stable contact lenses and the comfort of wearing soft contact lenses, so-called hybrid lenses have been developed since 2001 and are now offered by some manufacturers. They have the oxygen-permeable core of a dimensionally stable contact lens and a soft casing. In 2005 they were approved for the American market. In particular, patients who suffer from keratoconus and previously required dimensionally stable contact lenses can benefit from the comfort of a soft contact lens.

RGP contact lenses versus soft contact lenses

The choice between RGP contact lenses (rigid gas permeable; dimensionally stable oxygen permeable) or soft contact lenses depends on the wearer's habits, but can also be influenced by medical aspects (some astigmatism can be corrected better with dimensionally stable lenses). Due to the significantly better flushing of the RGP lens, the corneal surface is better supplied with nutrients than with soft lenses; At the same time, metabolic waste products (such as pyruvate, lactate) are better flushed out. Dimensionally stable contact lenses have the advantage of not being able to dry out. Another aspect is the frequency of wearing: when worn occasionally, e.g. B. in sports activities, the soft contact lenses are usually cheaper. When worn on a daily basis, dimensionally stable contact lenses have a cost advantage despite the higher purchase and adjustment costs, as they have to be replaced less frequently with good care. If the wearer's eyesight changes relatively quickly, e.g. B. at a young age, it can make more sense to use soft contact lenses in order not to often have to buy the relatively expensive dimensionally stable contact lenses. In strong winds or in a dusty environment, dimensionally stable contact lenses run the risk of foreign bodies causing pain to get under a dimensionally stable contact lens. Due to the almost direct adhesion of soft contact lenses to the surface of the eye and their expansion to below the edge of the eyelid, soft contact lenses sit more firmly in the eye than dimensionally stable ones, which also reduces the risk of loss. The risk of corneal infections is greater with soft contact lenses than with dimensionally stable contact lenses (3.5 versus 1.1 cases per 10,000 wearers).

It takes longer to get used to dimensionally stable contact lenses than to soft ones. While soft contact lenses are usually only felt to a small extent as foreign bodies on the first day of wearing, dimensionally stable contact lenses require a period of three to six weeks to get used to. Thereafter, dimensionally stable contact lenses must be worn continuously in order not to lose the familiarization effect. However, even after this period of getting used to it, many wearers feel a stronger foreign body feeling with dimensionally stable contact lenses than with soft contact lenses.

Lens functions

Contact lenses for correcting nearsightedness or farsightedness

The most common contact lenses are used to correct nearsightedness or farsightedness. In this case, be spherical lens shapes, aspherical lens shapes, or spherical lens molds used with aspherical edge region.

Toric contact lenses

With toric contact lenses by a conditional astigmatism is astigmatism corrected. In addition to the diopter value, the values ​​for the axis and cylinder of the astigmatism must also be taken into account during manufacture. The corneal curvature is compensated for by cylindrical parameters. The lens must sit in a defined position. This is accomplished through several methods that require careful customization. In addition to the diopter values, the eye size is determined for correct adjustment. In addition, the structure of the cornea must be recorded in order to correctly adapt the lens to this shape.

Contact lenses for correcting presbyopia

In the fourth decade of life, the human eye gradually loses the ability to adjust to close distances. This phenomenon is known as presbyopia or presbyopia . In rare cases, pathological changes or injuries to the eye may require close-up correction earlier. In contrast to conventional contact lenses, with which only far or near vision can be corrected, multifocal lenses have offered the possibility of clear vision at different distances since 1982. Multifocal lenses are divided into segment-shaped bifocal lenses or concentric multifocal lenses. The monovision technique is a special form. Which type of lens is used depends on the physiological conditions and the type of application. Multifocal lenses are manufactured as dimensionally stable contact lenses as well as soft contact lenses.

Segmented bifocal lenses

This manufacturing principle, which is also referred to as an alternating (alternating) system, usually consists of two segment-shaped optical zones with different effects. When looking into the distance, the eye sees through the upper optical zone that corrects for the distance. When looking up close, the eye is turned downwards, but the contact lens is pushed upwards by the influence of the lower eyelid and you can see through the near zone.

Concentric multifocal lenses

With this type of lens, two or more annular viewing zones are arranged concentrically. With modern contact lenses, the areas now flow smoothly into one another. The user can use different optical zones at the same time, hence the additional designation as "simultaneous system". The basics were already described by Collins and de Carle in the 1950s. The eye is offered the image of near and far at the same time, and it (unconsciously) selects the desired image.

Monovision technology

Multifocal contact lenses are not used here to correct the presbyopia, but one eye is compensated for the distance, the second eye for the near. When using this technique, however, there are limitations in binocular stereoscopic vision .

Night lenses

Another form of contact lenses are orthokeratological night lenses . These are used before sleep and left in the eyes overnight. During the gestation period, they correct the shape of the cornea of ​​the eye. This deformation is not permanent, but persists for a period of one to three days, during which clear vision is possible without visual aids.

Bandage lenses

Bandage lenses are used by the ophthalmologist for injuries to the cornea and can remain there for up to four weeks.

Cosmetic contact lenses

Various cosmetic contact lenses

Colored or painted contact lenses (also called motif lenses ) are mainly used for aesthetic or cosmetic purposes. A medical indication for colored contact lenses (iris lenses) is in the presence of light sensitivity. Their optical functions are worse than those of conventional contact lenses. They are available in all common colors and motifs, for example with reptile or manga motifs, which are becoming increasingly popular at carnival , Halloween and theme parties . The version “ Sclera -Lens” (German “full shell contact lens”) can cover the whole eye. According to the manufacturer, such contact lenses may be worn for a maximum of six hours with the use of eye drops and are not for sale in Germany for private individuals. Because of their size, a full-shell contact lens is more difficult to insert than a normal soft contact lens.

Sea-U freediving lens

Sea-U freediving lens

The pressure inside a diving mask has to be consciously adjusted several times while diving. It does this by blowing air from your lungs through your nose. This fact is only possible to a limited extent for freedivers, as they only have one lung filling of air with them and the repeated pressure equalization in the mask leads to a significant loss of air and thus to shorter dives. Especially at greater depths, the volume of the compressed lung is too small for this. In order to eliminate the need for this pressure equalization, contact lens specialist Rainer Holland developed the Sea-U lens , which enables free divers to see clearly underwater without using a diving mask. However, production has since been discontinued.

Corrective properties compared to glasses

In the case of severe myopia, contact lenses have the advantage that what is seen is only insignificantly reduced in size due to the direct fit on the eye, unlike with glasses . On the other hand, with strong farsightedness, what is seen is hardly enlarged, so the field of vision is not significantly reduced compared to a person with normal vision . The visual acuity that can be achieved with dimensionally stable contact lenses is often higher than the visual acuity that can be achieved with glasses, since the physiologically always existing irregular component of astigmatism is partly compensated for by the tear fluid that collects under the lens, also known as the "tear lens". In all cases, the field of view is not restricted by the edge of the glasses and the eyes can follow natural movement patterns. Contact lenses often have a light tint to make them easier to use.

Adjustment and maintenance

Commercially available container for disinfecting or storing soft contact lenses
Lid of a contact lens case with gas outlet openings

Contact lenses that are not properly and properly fitted can damage the eye. Therefore, the adjustment ( contactology ) should be carried out by an appropriately trained specialist, usually an ophthalmologist , an optician or an optometrist . This ensures the best possible result and is liable in the event of problems within the legal framework. The fitter takes into account the individual shape of the eye as well as the power of the eyelids when blinking. Particular attention is paid to the tear film, the properties of which determine the respective lens material.

Pay attention to the length of time the contact lenses are worn. Daily lenses are a special case, as they are only used for certain situations (sport, work, when glasses cannot be worn for safety reasons, etc.). The daily lenses are removed from the eye and disposed of after a few hours, at the latest after 16 hours. Soft contact lenses should be replaced regularly. The manufacturers offer the customer several variants to choose from. Periods of one to two weeks up to twelve months are possible here. The aging of the contact lenses reduces their comfort. The most common mistake in use is that replacement lenses are worn for too long. After the period of use has expired, the eye is supplied with significantly less nutrients, which leads to the risks mentioned below. Therefore, the duration of wearing the contact lenses should always be agreed with the ophthalmologist and optometrist.

The contact lens wearer should attend regular follow-up appointments to avoid risks. Good hygiene must be ensured by selecting the contact lens care products that match the lens material and changing the fluids regularly. Contact lenses age and can then show signs of use, deposits and damage.

Children and contact lenses

Even children can wear contact lenses easily and successfully as soon as they are physically and mentally able to do so. The contact lens fitter should discuss and practice the correct handling and, in particular, the care of contact lenses with the child and the parents. In the case of smaller children, parents should actively support their child, especially during the acclimatization phase, with inserting and removing them, as well as with the correct care of the contact lenses. As a rule, however, children learn how to use the lenses quickly.

Risks and Side Effects

Oxygen deficiency under contact lenses leads to a variety of impairments in the function of the cornea. The main side effects of contact lenses are hyperemia in the conjunctiva or limbus , neovascularization, and conjunctivitis , especially keratoconjunctivitis sicca and giant papillary conjunctivitis .

By infection with bacteria, fungi or amoebae induced corneal inflammation are another risk, especially soft contact lenses. About 90 percent of all keratitis cases are contact lens wearers; In an article from 2013, “Der Spiegel” also states that around 4,000 of the 2.5 million wearers of soft contact lenses across Germany are affected each year.

The risk of all side effects mentioned generally increases the longer it is worn. The likelihood of infectious conjunctivitis and corneal inflammation can be reduced by observing the hygiene regulations for handling contact lenses. Contact lenses should not be cleaned with tap water. An increased risk of acanthamoeba and fusarium (a fungus) keratitis was also found with the use of certain contact lens cleaning solutions. It was not a question of product batches contaminated ex works, but rather a fundamentally inadequate disinfecting capacity of the cleaning systems in question, which have since been withdrawn from the market.

It can also be assumed that even a contact lens with a high average transmissibility (oxygen permeability) can lead to local impairment of the cornea if areas of the contact lens are thick enough to cause hypoxia of the epithelial cells below. Holden and Mertz defined the minimum oxygen transmissibility (Dk / t) as 24 · 10 −9 mL (O 2 ) / (cm 2 · s · mmHg) for wear throughout the day and 87 · 10 −9 mL (O 2 ) / (cm 2 · s · mmHg) for nighttime wear. The criterion for this value is the occurrence of overnight edema in a range of only 3–4%.

Restrictions on wearing

sauna

The dry air and regular sauna infusions can irritate the eyes. Furthermore, deposits form on the lens. It is therefore advisable to use contact lenses when visiting the sauna, which are very permeable to oxygen, which can be recognized by a high Dk value or Dk / t value of the lenses.

swim

Contact lenses are often lost while swimming. This is even more likely with dimensionally stable lenses than with soft contact lenses, since soft lenses attach more firmly to the cornea. The material of the contact lenses can also be deformed by chlorine and salt water, which would impair the optical properties of the lenses.

Swimming or bathing with contact lenses (and generally from bringing soft contact lenses into contact with water - including swimming pool or tap water!) Is generally not recommended today, as the lenses can be colonized by microorganisms living in water. Instead, prescription swimming goggles could be used. In the medical literature there are various descriptions of cases in which contact lens wearers contracted severe corneal infections with acanthamoeba , fungi or bacteria in connection with the lenses coming into contact with water .

Scuba diving

The use of soft daily lenses is recommended. If you lose the lenses, the financial loss is small in contrast to monthly or annual lenses or especially diving masks with optical glasses. Daily lenses are also generally considerably cheaper than, for example, over a longer period of time. B. Diving masks with optical glasses. If the optical properties of the eye have changed after a long period of time, a new (expensive) diving mask is not required, only new daily lenses with the changed diopter values ​​need to be procured; the previous diving mask without correction can still be used.

Soft daily lenses are currently (August 2012) available from specialist retailers at prices starting at around 40 cents each. This results in a price of approx. 8 euros for 10 dives on different days.

The high water pressure can lead to poor vision when quickly surfacing with dimensionally stable contact lenses, as air bubbles emerging from the cornea collect under the lens. From a medical point of view, however, this does not pose a health risk. No negative or harmful effects have been found when diving with soft contact lenses.

However, for health reasons, rapid surfacing should generally be avoided as it involves considerable risks.

jobs

In most professions, wearing contact lenses is not a disadvantage compared to glasses. In rooms with low humidity or air conditioning, wearing contact lenses is problematic as it quickly leads to tear film problems ("dry eyes") and thus irritation of the surface of the eye can. The selection of a suitable lens material and the use of a care product tailored to the material and tear film are helpful here. Activities in a dusty environment, e.g. B. as a baker (flour), in road construction or even in the craft, as far as it is dusty at the workplace, are extremely poor conditions for wearing contact lenses, with well-rinsed (i.e. healthier) RGP lenses being easier to irritate from dust particles under the Lens can get. Which professions can lead to long-term problems when wearing contact lenses should be checked in a conversation with an ophthalmologist or optician.

pregnancy

Due to hormonal changes, e.g. B. during pregnancy, when taking hormone preparations ("pill"), with thyroid diseases, etc., the composition of the tear fluid can change and thus lead to the symptoms of "dry eyes".

Manufacturer

Web links

Commons : Contact Lenses  - Album with pictures, videos and audio files
Wiktionary: contact lens  - explanations of meanings, word origins, synonyms, translations

Individual evidence

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  2. ↑ RF Heitz, JM Enoch: Leonardo da Vinci: An assessment on his discourses on image formation in the eye. In: Adrianna Fiorentini, David L. Guyton, Irwin M. Siegel: Advances in Diagnostic Visual Optics. Proceedings of the Third International Symposium, Tirrenia, Italy, May 1-4, 1986. Springer, Berlin et al. 1987, ISBN 3-540-17585-7 , pp. 19-26.
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  5. ^ Heinrich Wöhlk: inventor of the contact lenses. In: Fogis. January 24, 2011, archived from the original on May 31, 2014 ; accessed on February 18, 2016 .
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  9. ↑ Dimensionally stable contact lenses are not hard. (PDF) Professional Association of Ophthalmologists in Germany, accessed on February 18, 2016 .
  10. ↑ Patrick H. Benz: Hydrogel vs. Silicone Hydrogel Materials. ( Memento from June 26, 2011 in the Internet Archive ) (PDF; 209 kB).
  11. ↑ Loretta Szczotka-Flynn: Improving Ocular Health and Comfort With Silicone Hydrogel Contact Lenses. In: Contact Lens Spectrum. June 2007, ISSN  1085-2395 , accessed June 11, 2013.
  12. ^ Brian Chou: The Evolution of Silicone Hydrogel Lenses. In: Contact Lens Spectrum. June 2006, accessed June 11, 2013.
  13. ↑ SynergEyes: ClearKone Lenses. Retrieved March 19, 2020 . SynergEyes, Inc. Launches New Hybrid Lens Design for Keratoconus Patients ( Memento from December 22, 2009 in the Internet Archive )
  14. ↑ Kam H. Cheng, Siu L. Leung, Hans W. Hoekman, W. Houdijn Beekhuis, Paul GH Mulder, Annette JM Geerards, Aize Kijlstra: Incidence of contact-lens-associated microbial keratitis and its related morbidity. In: The Lancet. Vol. 354, No. 9174, July 1999, pp. 181-185, doi: 10.1016 / S0140-6736 (98) 09385-4 .
  15. ↑ Peter Zimmer: In the eye of the beholder . In: Frankfurter Allgemeine Sonntagszeitung . No. 11, March 15, 2020, p. 42 .
  16. ↑ Toric contact lenses. Accessed January 21, 2020 .
  17. ^ JW de Carle: The De Carle bifocal contact lens. In: Contacto. Vol. 3, 1959, ISSN  0045-8317 , pp. 5-9.
  18. ↑ Dr. Dieter Schnell: Modern diving medicine: manual for diving instructors, divers and doctors . Ed .: Ch. Klingmann and K. Tetzlaff. 1st edition. 2007, ISBN 978-3-87247-645-6 , pp. 449-458 ( asu-arbeitsmedizin.com ). Modern diving medicine: manual for diving instructors, divers and doctors ( Memento from January 31, 2017 in the Internet Archive )
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  20. ↑ Contact lens - Lexicon of optics . ( Spektrum.de [accessed on November 28, 2017]).
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  23. ↑ a b Gerlinde Gukelberger-Felix: Danger of contact lenses - parasites in the eye. In: spiegel.de. September 12, 2013. Retrieved June 19, 2017 .
  24. ↑ Felicitas Witte: Pathogens in the eye. Süddeutsche Zeitung, May 17, 2010, accessed on June 19, 2017 .
  25. ↑ EY Tu, CE Joslin: Recent outbreaks of atypical contact lens-related keratitis: what have we learned? In: American Journal of Ophthalmology . tape 150 , no. 5 , 2010, p. 602-608 , PMID 21036209 (English).
  26. ^ AB Zimmerman, K. Richdale, GL Mitchell, BT Kinoshita, DY Lam, H. Wagner, L. Sorbara, RL Chalmers, SA Collier, JR Cope, MM Rao, MJ Beach, JS Yoder: Water Exposure is a Common Risk Behavior Among Soft and Gas-Permeable Contact Lens Wearers . In: Cornea . 2017, PMID 28410356 (English).
  27. ↑ T. Sengor, SA Kurna, A. Altun, M. Irkec, SF Aki, S. Aksoy: Contact Lens-Related Acanthamoeba Keratitis and Accompanying Dacryoadenitis . In: Eye Contact Lens . tape 41 , no. 4 , 2015, p. 204-209 , PMID 25603441 (English).
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