Keratoconus - Causes, Symptoms and Diagnosis
What Causes Keratoconus?
The exact cause of keratoconus is unknown. There are many theories based on research and its association with other conditions. However, no one theory explains it all and it may be caused by a combination of things.
It is believed that genetics, the environment and the endocrine system all play a role in keratoconus.
Genetic
One scientific view is that keratoconus is developmental (i.e., genetic) in origin because in some cases there does appear to be a familial association. From the presently available information there is less than a one in ten chance that a blood relative of a keratoconic patient will have keratoconus. The majority of patients with keratoconus do not have other family members with the disease. Some studies show that keratoconic corneas lack important anchoring fibrils that structurally stabilize the anterior cornea. This increased flexibility allows that cornea to “bulge forward” into a cone-shaped appearance.
Environmental
Eye Rubbing
Keratoconic corneas are more easily damaged by minor trauma such as eye rubbing. Poorly fitted contact lenses (that rub against the irregularity of the KC cornea) have been suggested as a possible cause of keratoconus. This has not been proven and remains questionable.
Allergies
Many who have keratoconus report vigorous eye rubbing and also have allergies (which cause eye itching and irritation, leading to eye rubbing), however the link to allergic disease also remains unclear. A higher percentage of keratoconic patients have atopic disease than the general population. Disorders such as hay fever, eczema, asthma, and food allergies are all considered atopic diseases. Those with keratoconus are advised to avoid eye rubbing as much as possible.
Oxidative Stress
Some studies indicate an abnormal processing of the superoxide radicals in the keratoconic cornea and an involvement of oxidative stress in the pathogenesis of this disease. Keratoconic corneas lack the ability to self-repair routine damage easily repaired by normal corneas. Like any tissues in the body, the cornea creates harmful byproducts of cell metabolism called free radicals. Normal corneas, like any other body tissue, have a defense system in place to neutralize these free radicals so they don’t damage the collagen, the structural part of the cornea, weakening it and causing the cornea to thin and bulge. The keratoconic cornea does not posses the ability to eliminate the free radicals so they stay in the tissue and can cause structural damage.
Hormonal
Another hypothesis is that the endocrine system may be involved because keratoconus is generally first detected at puberty and progresses during pregnancy. This theory is still controversial and has not been proven.
Symptoms of Keratoconus
The earliest signs of keratoconus are usually blurring of vision and the need for frequent changes in spectacle prescription, or blurred vision that cannot be corrected with glasses.
Symptoms of keratoconus generally begin in late teenage years or early twenties, but can start at any time. Other symptoms include:
- Increased light sensitivity
- Difficultly driving at night
- Halo’s and ghosting especially at night
- Eye strain
- Headaches and general eye pain
- Eye irritation, excessive eye rubbing
Keratoconus, especially in the early stages can be difficult to diagnose and all of the above symptoms could be associated with other eye problems. Simply recognizing symptoms does not by itself diagnose keratoconus. Keratoconus requires a diagnosis from a competent optometrist or ophthalmologist who is trained in not only recognizing the symptoms but also observing signs of keratoconus through direct measurement as well as inspection of the cornea at a microscopic level using a slit lamp.
The Diagnosis of Keratoconus
Keratoconus can usually be diagnosed with a slit-lamp examination. The classic signs of keratoconus that the optometrist will see when examining your eyes include:
- Corneal thinning
- Fleischer’s ring (an iron colored ring surrounding the cone)
- Vogt’s striae (stress lines caused by corneal thinning)
- Apical scarring (scarring at the apex of the cone)
The optometrist will also measure the curvature of the cornea. This is done by:
- Keratometry – an instrument that shines a pattern of light onto the cornea. The shape of the reflection of the pattern tells the doctor how the eye is curved.
- Corneal topography – a computerized instrument that takes three-dimensional “maps” of the cornea.
A typical corneal topography map looks like this:
Corneal topography has facilitated the diagnosis of keratoconus, helping establish the diagnosis earlier, follow progression more accurately and differentiate keratoconus from other conditions.
With thanks to the National Keratoconus Foundation