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