What is keratoconus?

Keratoconus is a pathologic bulging of the cornea (the clear window at the front of the eye), usually leading to abnormally high and irregular astigmatism.

Keratoconus typically first occurs in children and young adults but can affect people of all ages. What happens in keratoconus is that one part of the cornea becomes weakened. The normal pressure inside of the eye then causes the cornea to progressively bulge forwards at this weak point. This results in the classic, asymmetric cone shape with its top becoming thinner and thinner. As the cornea continues to weaken and the cone increases in size, the patients experience symptoms like blurred, sometimes distorted vision, or even double vision. These symptoms occur due to an increasing short-sightedness (myopia) and irregular astigmatism and can’t be satisfactorily corrected with spectacles in advanced cases. In most patients, both eyes are affected, but usually one eye is affected more than the other.

There is no one initial cause known for keratoconus, but there are several risk factors that can lead to or promote keratoconus. The disease is usually more aggressive in children.

As keratoconus often is a progressive disease it should be diagnosed and treated as early as possible to avoid severe visual impairment. Worldwide, keratoconus is the leading cause of preventable blindness in children and adolescents. The sooner it is detected and treated, the better the prognosis for the vision.

The term “keratoconus” comes from the Greek word for horn, “kéras”, and the Latin word for cone, “conus”.

How can you tell that you have keratoconus?

If you are experiencing any of the following symptoms you should book an appointment with a cornea specialist, especially if one or more risk factors apply to you. The faster your symptoms deteriorate, the faster you should book an appointment. If you have already been diagnosed with keratoconus, please look out for symptoms in your family, especially in your children or nieces and nephews, and let them have screened by a specialist.


  • Blurred, distorted or/and double vision
  • Continually changing prescriptions
  • Decreased eyesight despite new glasses
  • Better vision with contact lenses than with glasses
  • Increase of symptoms in the dark / twilight (eg. driving at night)
  • One eye is worse than the other
  • Light sensitivity
  • Halos / glare
The symptoms can occur in people who already wear visual aids but also in people whose vision has always been good. In many people, the first sign is that their glasses prescription keeps changing or they suddenly have a bad vision, even though they never needed glasses before. This can be in only one eye or in both eyes. The reason for these symptoms is the new shape of the cornea. Usually, the patients become more myopic and develop astigmatism. As the disease progresses and the cone continues to get bigger, people start getting blurred or distorted vision that glasses can no longer correct, because the cornea has an asymmetric shape. Many people see double or multiple images, and their vision gets worse during twilight or in darkness when the pupil is dilated. People also become more sensitive to light and glare, and this can cause problems when driving at night because the headlights from other cars can make it very hard to see anything at all.

Risk factors

  • Age under 20 years
  • Family history of keratoconus
  • Change/Imbalance in hormones (eg. Pregnancy, thyroid dysfunction, estrogen-like drug therapy)
  • Genetic disorders that affect collagen (eg. Ehlers-Danlos syndrome, Marfan syndrome, Trisomy 21/Down syndrome)
  • Allergies
  • Autoimmune diseases
  • Former corneal surgeries
  • Eye rubbing

Eye rubbing is known to make keratoconus worse if a person already has it, but experts still disagree about whether eye rubbing on its own can cause keratoconus in the first place. Having said that, all experts agree that people should not rub their eyes.

Hormonal changes can cause keratoconus. Pregnancy can cause the cornea to become softer, and this can either cause a cone to form in an already weak cornea, or make an existing cone get worse. The same is true for imbalances in thyroid hormone, and certain estrogen-like drug therapies (for example, the treatment of endometriosis or hormone replacement therapy) can also have this effect.

Collagen is an important part of the cornea and plays a large role in maintaining its strength and shape. People with genetic disorders that affect collagen, such as Ehlers-Danlos syndrome, Marfan syndrome and Trisomy 21 (Down syndrome) often have keratoconus.

How often does keratoconus occur?

The occurrence of keratoconus varies hugely by geographical location, In some countries, only 0.05% of the population may have keratoconus, in others up to 5% of the young people have keratoconus. The ELZA Institute is running a global study on this topic in many countries. We started collecting data on 4 continents back in 2018 already.

Keratoconus affects far more young people than older people, unfortunately, the disease usually progresses far faster in children and young adults than in older people. This means that it is important that in children, treatment to stop keratoconus progression (corneal cross-linking, or CXL) is performed as soon as possible after diagnosis.

Keratoconus prevalence

How do doctors diagnose keratoconus?

Keratoconus is often discovered by accident – normally when patients have made an appointment for a different reason, like when their glasses no longer have the correct prescription, or their contact lenses no longer give them good vision.

The first step in any keratoconus diagnosis is to discuss your medical history. The ophthalmologist will ask questions like:

  • What symptoms are you experiencing and how intense are they?
  • Do the symptoms affect one or both eyes?
  • When did you first notice them and did they get worse?
  • Are the symptoms worse at night/ in the dark than during the day?
  • Does your family have a history of keratoconus?
  • Do you have any other eye diseases or have you ever had eye surgeries?
  • Do you have any allergic or autoimmune diseases?
  • Are you pregnant?

We then perform a series of eye exams as described below.

Slit lamp

The slit lamp is a microscope that shines a thin strip of bright light on the eye. This allows the doctor to examine your cornea in detail and see any changes related to the disease. For example, in advanced cones, the doctor can even see stretch marks in the cornea, much like the skin of someone who is pregnant!


The next examination is refraction, either with special glasses or a device called phoropter. This is the device where we swap lenses to find what your refractive error is and to find the best lens prescription to correct it. It’s important to document what your refractive error is in each eye at every visit, so we can see if the disease is stable or progressing. These assessments also make sure whatever corrective method (e.g. glasses or contact lenses) used gives the patient the right amount of optical correction.

The most important exam – and the exam that can detect even very early stages of the disease – is corneal tomography. The instrument creates a detailed map of the cornea’s shape and thickness, and can show the doctor the exact location of the cone. The thickness measurements show us how far the disease has progressed and what treatment options are possible.

Progression and prognosis for keratoconus

It is important to treat progressive keratoconus swiftly. If the disease continues to progress and is left untreated, this results in an ever-thinner cornea and larger cone. The myopia and astigmatism progressively worsen, decreasing the visual acuity and making vision correction with glasses and soft contact lenses increasingly difficult.

In highly advanced cases, a corneal hydrops will develop. This means, that the cornea is stretched to such an extent, that liquid from inside of the eye penetrates into the cornea and makes it opaque. This obstructs the vision even more and might leave a scar.

In very advanced disease, if the eye is still left untreated, a keratoconus can progress further to a “corneal perforation” – the cornea becomes torn, and the contents of the eye can start to leak out. This is called a “globe rupture”, which is a catastrophic event which can result in the loss of the eye. However, this is very rarely seen.

In some cases, if the keratoconus is not progressive, the symptoms stabilize as well. However, a progression can only be excluded by periodic examinations with appropriate devices.

CXL at the slit lamp

Keratoconus treatment

Regardless of the degree of keratoconus, there are always treatment options. They can be divided into two approaches: stopping keratoconus progression and improving your vision.

Stopping keratoconus progression

The reason behind the progression is the weak cornea. The treatment, corneal cross-linking (CXL) is used to strengthen the cornea and can stop keratoconus progression. This is very important to avoid deterioration of the disease. If the keratoconus remains untreated, then the cornea can become too thin for cross-linking to be performed. In these cases, the most common treatment option is to replace the cornea with a donor cornea – in other words, corneal transplant surgery.

Improving vision with keratoconus

Once the CXL has been performed and/or the keratoconus is stable, we can then start to try and improve vision. In light cases, glasses might still give a patient a satisfactory vision. If that is not the case, a special type of contact lenses (scleral contact lenses) can be used – or in some cases, laser surgery. However, it’s important to understand that the earlier the disease is treated with CXL, the easier it is to improve vision with these approaches.


Is Keratoconus Rare?

Keratoconus and Corneal Transplants

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Augeninstitut ELZA
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Serena Fazio
Serena Fazio
11:15 06 Mar 22
I have been to the ELZA clinic to have surgery for my miopy, as my eyes were rejecting the contacts and I was tired of... wearing glasses. From the first preliminary visit, to the actual surgery and post-surgery care Dr. Hafezi and all his collaborators have been extremely professional, considerate and helpful. All the steps of the (very short!) surgery were thoroughly explained to me in order to be as calm as possible, together with the medication plan and precautions to be aware of so that my eyes could heal in the best way possible. By following their exact instructions, the healing process has been very successful and smooth, and after about one week I was able to see perfectly. I absolutely recommend this team and their expertise!read more
Robin A
Robin A
11:43 16 Feb 22
Top experts and professional team. Highly recommended
Thunder Shiviah
Thunder Shiviah
14:05 23 Nov 21
After some research on local options I decided to go with ELZA since it stood out as the best. The operation and the... post-operation recovery went extremely smooth (something I was worried about with PRK). Now my vision is much better than I had hoped and I have no side effects such as dry eye or night vision problems. Thank you!read more
Squitieri Elias
Squitieri Elias
12:43 08 Sep 21
Die Behandlungen waren bei mir erfolgreich, alle waren sehr nett und haben mein Leben vereinfacht.Danke
Eliane Bossart
Eliane Bossart
13:01 05 Sep 21
Vor einem Jahr war ich einer ganz verzweifelten Situation und total im Stich gelassen. Meine Augen wurden aufgrund... eines ausgeprägten Kerakotonus immer schlechter, ich hatte Angst und war alleine mit meinen Problemen. Zudem vertrug ich die Kontaktlinsen nur noch ganz schlecht und hatte jeden Tag Schmerzen.Professor Hafezi hat mir mit zwei Operationen wieder das auf Grund der Situation mögliche an Lebensqualität zurückgebracht. Es war ein starpaziöses Jahr mit vielen Entbehrungen aber es hat sich gelohnt! Herzlichen Dank fuer die Unterstü more
Gabriela Meyer
Gabriela Meyer
18:32 22 Aug 21
Ich wurde von meiner Optikerin auf Prof. Dr. Dr. Hafezi aufmerksam gemacht. Es war mir vorher nicht bewusst, dass meine... Augenkrankheit (Keratokonus) operativ mittels Cross Linking behandelt und so gestoppt werden kann. Die Beratung und Behandlung war sehr kompetent und ich fühlte mich jederzeit wohl. Die Operation verlief gut und das Ergebnis ist more
11:38 11 Aug 21
Ich bin sehr glücklich, dass ich das Elza Institute gefunden habe. Ich wurde von anderen Augenärzten abgewiesen, da... meine Augen zu kompliziert/schwierig zu behandeln waren. Prof. Dr. Dr. Hafezi konnte mir jedoch helfen und ich bin sehr glücklich und zufrieden mit dem Resultat. Vielen Dank!read more
Till B
Till B
08:30 19 Jul 21
Ich habe eine überaus kompetente Beratung und Behandlung erlebt. Die gesamte Betreuung war sehr freundlich und... professionell. Herzlichen Dank!read more
Thomas S.
Thomas S.
09:37 07 Jul 21
My left eye had to be operated on because of a cataract. As I had an Artiflex lens implanted a few years ago, it had to... be removed first before a modern lens could be implanted to correct the cataract. Prof. Hafezi treated me in an very competent and friendly manner. I am very happy with the more
Selma A. Rahim
Selma A. Rahim
19:45 02 Jul 21
Dr. Hafezi.. the KING OF CXL🤴
Gianluca Ricci
Gianluca Ricci
12:46 10 Apr 21
Great team and service!
05:36 08 Apr 21
Excellent surgeon
Steven H.A
Steven H.A
16:13 11 Jan 21
Prof. F. Hafezi s expertise is enormous and he has a very pleasant and calm nature which gives the patient... security.Thank youread more
Online Commande
Online Commande
09:19 05 Dec 20
Totally creepy, very arrogant Prof.He just want your money.It may explain, why this Prof. is not in the center of the... city of Zürich and why he has been thrown away from University of more
Elena Churilova
Elena Churilova
10:06 17 Nov 20
At the moment, 3 months have passed since the moment I made laser vision correction in this clinic. and I can say that... I am happy that I chose this particular clinic and Prof. F. Hafezi. The entire staff of the clinic is very friendly, treats patients with sympathy and patience if they are nervous before surgery (my big gratitude to Aida Alili for all support and patience). The doctor Hafezi and other doctors of the clinic are very professional and ready to explain to you as many times as you need. I can only recommend!read more
Ashley Faulkes
Ashley Faulkes
15:30 21 Mar 16
Professor Hafezi and the team at the ELZA Institute have done an amazing job of creating a first class eye clinic, with... cutting edge technology and support. I went there for a dry eye issue and other issues with my prescription, and they were easily able to help me and put me on the road to better vision! High recommend them to anyone in the Zurich/Aargau more
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