from Wikipedia, the free encyclopedia
Classification according to ICD-10
H18.6 Keratoconus
H19.8 Keratoconus in Down syndrome
Q13.4 Congenital keratoconus
Q13.9 Congenital malformation of the anterior segment of the eye
Z94.7 Condition after keratoplasty
ICD-10 online (WHO version 2019)

The eye disease keratoconus (from Greek κέρας keras 'horn', Latin conus 'cone') describes the progressive thinning and conical deformation of the cornea of ​​the eye . The disease is always bilateral, but can be weaker in one eye or not become symptomatic at all (Forme Fruste Keratoconus). The disease is therefore characterized by two properties:

  1. Progression (development): The cornea becomes thinner and more pointed
  2. Visual impairment: Due to the irregular deformation of the cornea, the visual acuity decreases.

Usually those affected are nearsighted . However, this nearsightedness cannot be completely corrected with a visual aid , since the conical corneal protrusion causes an irregular corneal curvature ( astigmatism ).


Nottingham's seminal text on keratoconus, 1854

The German ophthalmologist Burkhard David Mauchart described an illness in his doctoral thesis in 1748 , which he called "Staphylom diaphanum". However, it was not until 1854 that the British doctor John Nottingham described keratoconus in more detail and also found that it is clearly different from other ectasias of the cornea. Nottingham reported cases of " conical cornea" and described several features of the disease such as diplopia , corneal weakening, and difficulty seeing with corrective lenses.

In 1859, surgeon William Bowman used an ophthalmoscope ( invented shortly before by Hermann von Helmholtz ) to more accurately diagnose keratoconus. Bowman inserted a fine hook through the cornea, pulling on the iris and expanding the pupil into a vertical slit like a cat's. He was able to use this method successfully on an 18-year-old woman.

In 1869 the disorder got its current name from the Swiss ophthalmologist Johann Friedrich Horner .


Keratoconus occurs in the countries of the western world in approx. 1 person per approx. 1000–2000 inhabitants. The frequency of occurrence is higher in countries of the Middle East and Asia. In Germany about 0.5 ‰ of the population, i. H. every 2000th (a total of around 40,000 people) affected, although this may vary depending on the region and examination methods. In Down syndrome , the number of cases is up to 15%.

The keratoconus usually becomes manifest between the ages of 20 and 30. But it can also become symptomatic from childhood up to the age of 40 or 50.


Simulation: left with normal eye, right with keratoconus in the 4th stage

The first signs are frequent eyeglass corrections with a change in the axis and changing eyesight, as well as increasing corneal curvature, often initially on one eye. Because it is a rare disease, symptoms in the early stages are often not associated with this eye disease. Most of those affected have switched from different ophthalmologists for years until they come across one who recognizes the disease. With keratoconus, those affected see phenomena such as, in some cases only in one eye. For example: "Double vision of objects" ( monocular diplopia ) , additional shadows on letters and objects, as well as streaks or star-shaped rays that seem to emanate from light sources.

In the initial stage, a reliable assessment of the symptoms is only possible through an analysis of the corneal surface, the back surface of the cornea, the corneal thickness and, if necessary, a cell count.

Further characteristics are hemosiderin rings (Fleischer's rings), known as keratoconus lines. A yellow-brown to green-brown color appears here, which surrounds the base of the cone as a half or closed circle, visible in good lighting. During the further course of the disease, superficial, irregular scars and opacities as well as tears in Descemet's membrane can become visible and Vogt's lines appear.

If the disease is advanced, keratoconus can be seen from the side with the naked eye. If corneal edema (fluid build-up in the cornea) occurs, it is acute keratoconus . This can heal after three to four months with scarring.

Rarely, tears in the posterior cornea can occur, so that fluid from the anterior chamber penetrates the cornea, resulting in hydrops or acute keratoconus. This also manifests itself in an acute, severe clouding of the cornea (you can see fog ). The hydrops usually regresses by itself.

root cause

The cause of the keratoconus is still not known , despite extensive studies (e.g. long-term studies in the USA with 40,000 affected people).

Ultrastructural studies show that the regular layering of the collagen lamellae in the cornea is broken. The arrangement of the collagen lamellae in an orthogonal layer is destroyed. The destruction probably takes place via proteolytic activity. A genetic disposition is known in 23% of cases ; the only possible gene is VSX1 (Visual system homeobox gene 1; KTCN1). Excessive rubbing on the eye and certain environmental factors etc. can also be considered. The subsequent biomechanical imbalance between pressure load ( intraocular pressure ) and decreasing tissue strength then maintains a cycle that is expressed in the progression of the disease.


The change in the surface of the cornea can often be compensated for with glasses in the beginning, if the keratoconus is not very pronounced. Some patients get along well with glasses for a very long time. At this stage, some patients also have several glasses with different strengths and visual axes, some of which are worn in combination with contact lenses , as the visual strength and axis can change over the course of days.

If the keratoconus progresses and the cornea changes significantly, the ametropia can usually be reduced with dimensionally stable contact lenses.

If sufficient vision can no longer be achieved even with contact lenses because the cone is very far advanced or the contact lenses can no longer be adjusted well, the defective cornea can be exchanged for a transplant. However, this only occurs in around 20% of cases. The transplant is carried out in an eye clinic. There the defective cornea is exchanged for a donor cornea or, more rarely, stabilized with other methods.


Marc Amsler

Marc Amsler (1891–1968) divided keratoconus into four stages as early as 1950 . Here is the extended table by Dieter Muckenhirn with the corneal eccentricity that has been added since the sagittal radius measurement (with an ophthalmometer).

Degree Amslerwinkel Central radii Visus goggles VisusCL 1 transparency Thickness HH 2 Exc. 3
1 0 ° - 3 ° > 7.5 1.0-0.8 > 1 normal 0.5 mm <0.8
2 4 ° - 9 ° 7.5 - 6.5 0.8-0.2 1.0-0.8 normal 0.5 mm <0.8
3 > 9 ° 6.5-5.8 0.2-0.1 0.8-0.4 slightly cloudy 0.25 mm 1.2-1.5
4th not measurable <5.8 <0.1 0.4-0.2 very cloudy <0.2 mm > 1.5

1 CL = contact lens 2 HH = cornea 3 exc. = Excavation, in anatomy a space is called that spreads like a bulge between other tissue structures.

Jörg Krumeich

The stage is determined when one of the respective characteristics applies. The corneal thickness refers to the thinnest measured part of the cornea.

Conical stages according to Krumeich:

stage Clinical Criteria
Stage 1
Stage 2
  • induced myopia and / or astigmatism of> 5 D to ≤8 D
  • Corneal radii ≤ 53 dpt
  • no central corneal scars
  • Corneal thickness ≥ 400 µm
Stage 3
  • induced myopia and / or astigmatism of> 8 D to ≤10 D
  • Corneal radii> 53 dpt
  • no central corneal scars
  • Corneal thickness 200–400 µm
Stage 4
  • Refraction not measurable
  • Corneal radii> 55 dpt
  • central scars
  • Corneal thickness ≤ 200 µm


These side effects do not have to occur in all people affected. The phenomena are individual, just as the development of keratoconus differs from eye to eye.


Every second patient suffers more or less from hypersensitivity. Examples for this are:

Hereditary diseases

An association (link) with various hereditary diseases is often observed:

The quality of tears is often impaired by such a secondary illness and can be subject to additional changes due to medication .


When a suspected keratoconus should retinoscopy be performed at irregular reflection (scissors phenomenon) already have an increased suspicion. A keratoscope (Placido disk) and a keratometry to check the corneal topography should be used for further examination.

Corneal topogram from a keratoconus eye

Diagnostic equipment

  • Retinoscope , the oldest measuring device, with keratoconus the typical “fish mouth effect” can be seen
  • Ophthalmometer (keratometer) for measuring corneal radii and adapt to contact lenses.
  • Slit lamp , also called a corneal microscope , for recognizing the corneal layers and thickness
  • Keratograph / Placido disk (video keratometer), for recording the surface structure
  • Pentacam (Scheimpflug camera ) and OrbScan for recording the topography of the front and back ( endothelium ), as well as calculating the thickness of the cornea
  • Optical coherence tomography (OCT) to record a cross section of the anterior segment of the eye, corneal thickness and the course of the surface can be documented


Pellucid marginal corneal degeneration

Particularly in the early stages, keratoconus can be mistaken for irregular corneal curvature or, due to inexperience, with pellucid marginal corneal degeneration (PMD). Other corneal degenerations that also cause thinning are the keratoglobus (affects the entire cornea). The keratectasia may be an initial stage of keratoconus.

Under Keratoconus posticus a curvature increase in the posterior cornea is understood the same time the corneal surface remains intact. There appears to be a link between keratoconus and keratoconus posticus.

With Fuchs endothelial dystrophy, however, the cornea thickens centrally.



One possibility for treatment is glasses , which are usually used at the beginning of the disease. Some ophthalmologists believe this option is better than contact lenses because contact lenses can trigger or at least make keratoconus worse. However, there is no evidence of this. Others report that treatment with hard contact lenses prevents further development of the corneal cone. There should even be a flattening of the cone tips.

It should be helpful to wear raster glasses with small holes in the lens. Through this point grid, the incident light beam is bundled and aligned in front of the eye. A cure or regression of the keratoconus cannot be achieved with this, however, there is no scientific proof of the effectiveness of the pinhole glasses.

contact lenses


method cases
soft lenses (standard) only exceptional cases, in the early stages
soft special lenses Alternative to dimensionally stable lenses 1
dimensionally stable lenses Means of choice
Scleral lenses (new generation) Alternative if the eyes are very sensitive 1
Duo system (piggyback system) only in rare cases 2

1 If there is too much pressure on the cornea and / or if the skin is too sensitive to dust

Soft lenses

In the early stages, soft lenses may be used for correction. At a later stage, however, this is no longer possible, as the lenses do not adapt to the cone and so no vision improvement is possible. Hard contact lenses should be adjusted here because the tear fluid in connection with the contact lens compensates for the unevenness of the cornea. In later stages, however, this can become increasingly difficult. A Kerasoft IC contact lens can be fitted for mild or moderate keratoconus. This is more gas-permeable than conventional soft contact lenses. It is difficult to adjust this with an advanced cone.

Soft lenses (piggyback system)

In some cases of intolerance to wear comfort with dimensionally stable contact lenses, special soft keratoconus contact lenses or soft, highly oxygen-permeable contact lenses can now be worn as carrier lenses (protective lenses) under the hard contact lens (piggyback system).

Dimensionally stable lenses (hybrid lenses)

Hard contact lens for a keratoconus

Dimensionally stable contact lenses are mostly used when glasses or soft lenses are no longer able to achieve adequate correction of the visual acuity, or when several images are seen due to corneal deformations.

The more the tip of the cornea, called the apex, bulges over time, the more the contact lens has to be curved, because the apex tip must not experience any pressure. At this advanced stage, special keratoconus lenses are individually fitted. These usually have to have a quadrant- specific shape in order to have a good and stable fit on the eye.

If the cone is very advanced, however, the image quality can deteriorate and the affected patient can no longer achieve 100% visual acuity. If the cone becomes more acute, a point is finally reached at which the normal dimensionally stable contact lens is no longer an effective treatment method. Be it that it can no longer hold, or that there is no longer any improvement in visual acuity, or that the lens has pressure points on the cornea. On the one hand, this is painful for the wearer, on the other hand, it is also not without risk, since the cornea is already thinned due to the keratoconus and damage can occur due to additional stress.

Then a corneal transplant must be considered. However, this only occurs in about 20% of all cases. Most patients get along well with contact lenses for a lifetime.

If even with dimensionally stable keratoconus lenses sufficient visual acuity cannot be achieved or these cannot be tolerated, scleral lenses or mini- scleral lenses can also be adapted. These cover the entire cornea and lie on the dermis.

The so-called hard-soft hybrid contact lenses represent a further possibility. They consist of a hard, dimensionally stable, oxygen-permeable core and a soft casing. These increase wearing comfort and reduce the irritation and intolerance that are often caused by the small, dimensionally stable lenses. Loss of a lens straight out of the eye is also less likely.

Scleral lenses

Special lenses

Janus lenses have a stable core and a soft outer area. Since these contact lenses are very complex to manufacture, they have never really caught on. This type of lens is not very gas permeable, so that the cornea is not adequately supplied with oxygen. Therefore, these lenses should only be used in special cases.

In rare cases (with high sensitivity or greatly increased sensitivity to dust) a “ piggyback system ” can also be used, in which a hard contact lens is fitted to a soft lens.

For patients with intolerance, or those who have problems in a dusty environment, there is a new supply option with HydroCone contact lenses (soft keratoconus lenses) to increase visual performance and comfort.


The aim of surgical treatments is visual rehabilitation (improvement of vision) and stopping the further development of the disease. The only effective method to date is cross-linking .

CrossLinking (CXL)

The ophthalmologist Theo Seiler is considered the discoverer and developer of crosslinking (collagen injury) , who also performed the first laser-guided radial cuts (RK / Radial Keratotomy ) of the cornea to eliminate myopia with the excimer laser . The effectiveness of this therapy in stopping the progression of keratoconus and thus possibly avoiding a corneal transplant has been proven in many studies. Theo Seiler has been honored by many international ophthalmological societies for his services to the treatment of keratoconus and is a welcome speaker at national and international congresses. Over the past 10 years, many different approaches have been clinically tested and different treatment protocols have been compared. Crosslinking prevents progression and is now also recommended by statutory health insurers in stages I and II. It is the only treatment method so far that has been proven to be able to stop the progression of keratoconus for several years. It may even be effective over the long term. Crosslinking has hardly any effect on a small number of those affected. The photochemical process mediated by riboflavin and ultraviolet radiation (UVA) cross-links the collagen of the cornea with one another, thus achieving a stabilizing effect. In order to be able to perform CXL, a corneal thickness of at least 400 µm is required. After the biomechanical stiffening of the cornea, a topographically guided transPRK or standard PRK is to be carried out with the excimer laser in order to return the cornea to an optimal, optically more effective contour and thus also to improve visual acuity. There are also treatment protocols that carry out the topographically guided PRK with subsequent crosslinking in one session. However, the simultaneous interaction of the two treatments seems to have a considerably stronger effect on the transparency of the cornea ("haze" formation) than a crosslinking treatment alone, whose low risk of haze formation has meanwhile been proven in the literature.

Whether the obvious successes of the crosslinking treatment justify doubts about worsening the prognosis of a corneal transplantation is doubted and remains to be seen.

Intracorneal Implants

Before a corneal transplant is performed in very advanced cases, intracorneal implants can be used to achieve visual rehabilitation and, in many cases, delay or even prevent the need for a corneal transplant.

ICRS - Intracorneal Ring Segments

An intrastromal corneal ring segment (ICR or ICRS or Intacs) is an implant for the cornea of ​​the eye. The ICRS have been in use since 1996. The ICR consists of two small ring segments that together have an inner diameter of 6.7 mm. These transparent plastic segments are made of the plastic polymethyl methacrylate (PMMA), the same material that has been implanted as a lens replacement in cataracts for around 30 years . They are pushed into (intra) the layers ( stroma ) of the cornea at the edge of the cornea, thereby flattening the central cornea. The tunnel incision required for this can be prepared with a blunt knife or with the femtosecond laser . Depending on the ring size, myopia can be between −1 dpt. and −4 dpt. Getting corrected. A corneal curvature should not be present.

The surgery should only be performed by an experienced corneal surgeon. The risk of a cutting error can be reduced by using the femtosecond laser. In the event of an over or under correction, the ring segments can in principle be exchanged or removed again. Because of the radial incision in the cornea, however, the wound must always be closed with a suture. A removal or an exchange can therefore only take place via the opening of the already scarred wound, and this must then be sutured again.

The ICRS are mostly used for visual rehabilitation of keratoconus. However, the segments have ends and can therefore often lead to pressure atrophy of the corneal tissue as a complication, which causes the segments to “grow out” of the corneal surface, which is referred to as “extrusion” or “corneal melting”.

CISIS (MyoRing)

A full ring implant ( MyoRing ) is inserted into the cornea to treat keratoconus. The treatment method is called CISIS (Corneal Intrastromal Implantation Surgery) and has been approved since around 2007. The ring is inserted into the cornea between an anterior and posterior corneal lamella in a virtual gap (closed corneal pocket). Because of the lamellar structure of the cornea, the corneal pocket is biomechanically neutral. The procedure can be combined with crosslinking in one treatment session. No seams are necessary. The MyoRing implantation can replace a corneal transplant in many cases. CISIS can no longer be used if the corneal thickness is less than 350 micrometers or the central K values ​​are above 60 diopters. The latest results show that the MyoRing not only leads to visual rehabilitation, but can also stop the progression of keratoconus because of its closed construction.

Corneal transplant (keratoplasty)

Corneal graft

Contact lenses may not be tolerated if, for example, the eye does not produce enough tear fluid. Then, despite a possibly better correction, a surgical intervention must be considered. Otherwise, a transplant is only carried out if sufficient visual acuity is no longer achieved with contact lenses (visual acuity below 0.3) or treatment with intra-corneal implants is no longer possible.

During a keratoplasty , the cornea is punched out so that only a small margin remains ( trepanation ). The cut-out piece is replaced by donor tissue and sewn with a double seam to make it watertight. The Heidelberg University Eye Clinic is the first in Germany to use a new laser device for corneal transplants, which may make it possible to dispense with sutures in the future. There is a lamellar (layered) keratoplasty and a perforating (penetrating) keratoplasty.

The goal must always be to preserve your own cornea for as long as possible. The healing process after a transplant can take up to two years and even after a transplant, around 85–90% of those affected have to wear dimensionally stable, mostly special contact lenses again. A hasty keratoplasty is not advisable, the alternatives listed below may also help. Most of them are relatively new or there are no long-term studies. When it comes to the question of which method makes sense in which stages, there are only guidelines, but the attending physician can best assess when which type of keratoplasty can help.


In addition to the methods mentioned, there are also other methods that are not discussed further here:

  • CKT Circular Keratotomy
  • Verisyse (Artisan) lens
    • The refractive epikeratophakia (EPI) is applied in stage II and III
    • Keraform treatment
    • conditionally with an excimer laser .
  • Keratoplasty
    • Perforating keratoplasty in the IV stage
    • Deep anterior lamellar keratoplasty (TLKP): "Deep anterior lamellar keratoplasty" (DALK), for advanced keratoconus
  • Keratotomy
    • Mini-Asymmetric Radial Keratotomy (MARK) designed by Marco Abbondanza. Stage I and II.
    • Radial asymmetric keratotomy (ARK or mini ARK) performed by Professor Massimo Lombardi. Although Lombardi has used this treatment since 1993, no scientific studies have been carried out to date.
    • Bowman Layer Transplant for advanced keratoconus

Laser treatment ( PRK , LASIK ) is contraindicated .

Other treatments such as hormone therapy , using vitamin D complexes or vitamin E as well as topical cortisone have not shown any sure success.

Prophylaxis (prevention)

According to all that is known so far, one cannot actively protect oneself against keratoconus, since the disease probably has at least one genetic disposition as an additional cause.

In general, it certainly makes sense to avoid anything that puts a lot of strain on the eyes and cornea. This is especially the "rubbing of the eyes", which is probably caused by too little tear fluid or too frequent screen work. Staying in rooms with dusty, smoky air or air from air conditioning systems is perceived by many as a burden.

In any case, it is an advantage to drink a lot, to exercise in the fresh air and to avoid smoky or dusty surroundings.

Many practitioners and those affected are also of the opinion that wearing contact lenses is a very significant burden on the cornea of ​​the eye and should be avoided as far as possible. To date, it has not been proven by studies that wearing contact lenses promotes keratoconus.

Reimbursement of costs (specific to Germany)

Since the health reform of 2004, it has proven difficult for health insurance companies to cover the costs of contact lenses . It is particularly difficult to get coverage in the early stages of fitting keratoconus lenses. Many of the alternatives mentioned above are also not paid for, as long-term studies are usually lacking or the surgical methods are controversial.

The current (2013) aids directory of the National Association of Statutory Health Insurance Funds lists so-called keratoconus lenses (custom-made) in the category "Optically corrective special lenses" , the costs of which are covered up to an agreed fixed amount under a corresponding medical indication.

According to a press release by the Federal Joint Committee on June 19, 2014, it was examined whether a treatment of keratoconus by means of UV crosslinking with riboflavin must be covered by the statutory health insurance .

The Federal Joint Committee (G-BA) decided on July 19, 2018 to include UV cross-linking with riboflavin in keratoconus in the catalog of services of the statutory health insurance. The decision came into force on October 12, 2018 after publication in the Federal Gazette ( BAnz AT October 11 , 2018 B2 ). On March 29, 2019, the Joint Evaluation Committee determined the compensation in the EBM. This means that the statutory health insurance companies can now offer their members this service, more than 20 years after the method was invented.


Hydrops (water in the cornea)

A prognosis for the course of the keratoconus is not possible because neither the causes of the disease nor the environmental influences on the course have been adequately investigated.

Some sufferers need a transplant after a short time, for example weeks or months after the first onset of the disease, while others can cope with glasses or contact lenses for decades or permanently.

The only observation that is generally confirmed by those affected and the practitioners is the experience that keratoconus often begins between the ages of 15 and 20 and often comes to a standstill between the ages of 40 and 50.


everyday life

A big problem is that lenses are always lost and have to be bought or applied for from health insurance companies. The eyes are also often overstimulated (reddening, extreme tearing, etc.) then only the removal of the contact lenses helps. The ophthalmologist must clarify whether there is any impairment in driving a motor vehicle .

Visual acuity can fluctuate several times a day. These changed visual conditions can lead to a deterioration in thought, memory and concentration processes.

Since keratoconus and its peculiarities are still relatively unknown in the population, explanations may be required (Why do you have to wear contact lenses and no glasses? Why do you see poorly today and good tomorrow? Why cannot you work just because the contact lens has been lost is? ...)

Driving license

According to a recommendation by the German Ophthalmological Society (DOG) and the Professional Association of Ophthalmologists in Germany (BVA), an annual follow-up examination is required for road traffic . A re-assessment is only possible after two years.


A class 2 medical certificate can only be issued through an examination by the Luftfahrt-Bundesamt or the responsible body. The minimum requirements are that the required visual performance is met with a visual aid and that regular checks are carried out. The intervals are determined by aero-medical centers or aero-medical experts.


In Germany, the state police , federal police , SEK , MEK and GSG have 9 exclusion criteria for contact lens wearers and for laser eye operations in the last 12 months. Sufficient eyesight even without glasses is required. The BKA demands that 100% vision aid must be seen with the good eye and at least 80% must be seen with the poor eye. After an operation you have to wait 12 months and the corneal thickness is sufficient to be able to work. Far-sightedness over 2.5 dpt. must not be present. The uncorrected visual performance must not be below 50% until one is 20 years old or below 30% from the age of 20. Further information on suitability for use can also be found in Police Service Regulation 300 (PDV 300) - Medical Assessment of Fitness for Police Service and Police Service Capacity (2012 edition).


  • In the Bundeswehr , keratoconus is given as grade VI (see: ZDv 46/1 Annexes 3.1 and 3.2). This means that military capability can be permanently excluded, the fitness level is therefore T5 (not fit for military service).
  • The soldier can be drafted to the Austrian Armed Forces after the position (draft) despite keratoconus.
  • In the Swiss Army , the soldier is unfit, unless the ametropia is operated on and certified as good after a medical certificate.

See also


Web links

Wiktionary: Keratoconus  - explanations of meanings, word origins, synonyms, translations

Individual evidence

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  2. ^ J. Nottingham: Practical observations on conical cornea: and on the short sight, and other defects of vision connected with it. J. Churchill, London 1854.
  3. W. Bowman: On conical cornea and its treatment by surgery. In: Ophthalmic Hosp Rep and JR Lond Ophthalmic Hosp. Volume 9, 1859, p. 157.
  4. JF Horner: For the treatment of keratoconus. In: Clinical monthly sheets for ophthalmology. 1869.
  5. a b R. Rochels: Acute Keratoconus in Down's syndrome. In: Albrecht von Graefes Archive for Clinical and Experimental Ophthalmology. Volume 212, 1979, pp. 117-128, doi: 10.1007 / BF00587603 .
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  35. UV crosslinking: corneal crosslinking with UVA radiation and riboflavin.
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