Causes of Keratoconus
The Big Mystery!
The exact cause of keratoconus remains elusive. Contributing factors seem to include genetic and possible hormonal factors but environmental factors may also play a role in the development of keratoconus.
In regard to genetic components, keratoconus appears to run sporadically in families but without any sort of direct inheritance pattern. Studies have suggested a 5% to 20% increase in chances of developing keratoconus if other family members have the condition. However, we have found no conclusive study that suggests how close an affected family must be to increase the chances of other family members developing the condition. Even identical twins with keratoconus (hard to find) have shown one twin to be affected and the other not effected. In our experience, keratoconus just seems to just “pop up” without any significant genetic predisposition.
Keratoconus is much more common in males than females suggesting a possible hormonal component but an exact mechanism has never been determined. Males also have an higher incidence of developing advanced keratoconus and the need for corneal transplantation.
The presence of atopic (skin) conditions such as dermatitis, eczema, and allergies are also a risk factor in the development of keratoconus. It is quite common to see all of these conditions in keratoconus patients but it is also far more common to see atopic conditions without the development of any keratoconus.
From an environmental perspective, there is some degree of correlation but no definitive numbers on the increase risk of keratoconus due to eye rubbing (feels really good but should be discouraged!). Excessive rubbing the eyes may put mechanical pressure on the cornea, further weakening the corneal structure. The cause of the itching/rubbing itself may be due to the underlying dermatitis and eczema that are often present in keratoconus patients. That then poses the question that does the itching cause the keratoconus or is the itching just a symptom of the associated skin problems and has nothing to do with the development of keratoconus?
Another possible environmental component to keratoconus may be the use of contact lenses, possibly more with rigid lenses, but once again no definitive numbers are available. Our personal experience is that we rarely see keratoconus develop in contact lens patients but rather most new keratoconus patients usually have no previous glasses or contact needs at all.
There has also been some debate on the correlation between refractive surgeries such as LASIK, SMILE, and PRK (link to refractive surgery article on our main site) and keratoconus. Any patient with even the slightest indication of keratoconus or other corneal destabilization conditions should never undergo refractive surgery as these procedures are designed to further thin the cornea in an attempt to focus the image on the retina. Rarely, refractive surgery patients can develop corneal ectasia (destabilization and irregular corneal thinning) which has similar symptoms and presentation of keratoconus but is obviously of a different mechanism.
On a cellular level, keratoconus appears to be caused by the loss of Bowman’s layer of the corneal. The cornea is essentially transparent skin tissue and similar to other skin, the cornea is composed of different and distinct layers. Bowman’s layer lies beneath the outermost layer (epithelium) of the cornea and the middle layer of the cornea which is called the stroma. The stroma is the thickest layer of the cornea and is responsible for the majority of its strength and stability. Without the presence of Bowman’s layer, the stromal layer comes in direct contact with the epithelium and this interaction appears to cause the weakening of the stromal collagen and destabilization of the corneal. How this interaction occurs chemically is still another mystery with several theories involving enzymes, free radicals, and chemical inhibitors with gigantically long chemical names which we won’t go into.
Although the true cause of keratoconus remains a mystery, ongoing research and new studies will hopefully shed some light on the root of this inconvenient condition. Until the cause can be determined and a cure found, effective treatment options must be used minimize the impact of keratoconus on the vision and lives of our patients.