Keratoconus is a condition that causes thinning and bulging of the clear front of the eye, the cornea. There are a variety of causative factors for keratoconus and more is being understood about its diagnosis and treatment all the time. This article will outline keratoconus, its causes, and its treatment.
What is Keratoconus?
The cornea is the front transparent surface of the eye and is largely responsible for focusing light onto the back of the eye, the retina, to allow for clear vision.
When there are deformities or changes in the curvature of the cornea, vision is therefore affected. Keratoconus is when the central cornea thins and the pressure from fluid inside the eye pushes it forward, leading to a bulging out and, if severe, a cone shape at the front of the eye.
It is a progressive disease with the highest rate of change in the teenage years and twenties with the process completing around age thirty.
The rate of progression can vary and the condition can sometimes progress later on in life as well or occur following a surgical procedure involving the cornea.
If the cornea is severely thinned and bulged, a break can occur where fluid from inside the eye drains into the cornea itself, leading to severe pain and visual disturbance. This acute condition, called hydrops, resolves with time and proper treatment.
What Causes Keratoconus to Occur?
Keratoconus is under constant study and causative factors are being investigated all the time. Family history and other genetics like ethnicity can play a role.
Excessive eye rubbing is an important risk factor as it increases eye pressure and strain on the cornea, leading to further degeneration.
Eye rubbing is associated with allergic or atopic conditions that cause the eyes to itch. Another possible cause can be refractive surgery, as this procedure involves altering and thinning the cornea in order to change the power of the eye.
This is why extensive testing of the cornea must be done before laser surgery to ensure that this does not occur.
Keratoconus is also associated with other genetic or connective tissue disorders, like Down syndrome and Marfan syndrome.
How is Keratoconus Treated?
In the early stages of keratoconus, it is often easily corrected with glasses or soft contact lenses. In the later stages, vision will be optimal only with the use of rigid gas permeable (RGP) lenses or scleral lenses.
RGP lenses are hard lenses that are smaller than the diameter of the colored part of the eye. These lenses will often take some time to get used to but provide excellent vision for patients.
They sit on the front surface of the eye and create a tear layer between the cornea and the lens that corrects the keratoconic irregularity and allows for better vision. Scleral lenses sit on the white part of the eye and are larger than RGP lenses.
They are also more comfortable and easier to get used to than RGP lenses. There are also hybrid lenses, which have a RGP center and soft contact lens edge, allowing for better comfort while still optimally correcting vision.
Corneal cross-linking is another treatment option for patients with keratoconus. This procedure helps to slow the progression of the cornea bulging outwards and maintains the integrity of the cornea as it is.
The procedure involves riboflavin (vitamin B2) being applied to the front surface of the eye with ultraviolet radiation exposure for 30 minutes. This makes the cornea stronger and more resilient against further change.
In severe and advanced stages of keratoconus, penetrating keratoplasty may be needed. This procedure involves transplanting a cornea from donor tissue and replacing the cornea of the patient.
Following the surgery, the patient will often be fit with a scleral lens for optimal vision.