Symptoms

People with early keratoconus typically notice a minor blurring of their vision and come to their clinician seeking corrective lenses for reading or driving.

At early stages, the symptoms of keratoconus may be no different from those of any other refractive defects of the eye. As the disease progresses, vision deteriorates, sometimes rapidly. Visual acuity becomes impaired at all distances, and night vision is often quite poor. Some individuals have vision in one eye that is markedly worse than that in the other eye. The disease is often bilateral, though asymmetrical in many patients. Some develop photophobia (sensitivity to bright light), eye strain from squinting in order to read, or itching in the eye, but there is normally little or no sensation of pain.

The classic symptom of keratoconus is the perception of multiple 'ghost' images, known as monocular polyopia. This effect is most clearly seen with a high contrast field, such as a point of light on a dark background. Instead of seeing just one point, a person with keratoconus sees many images of the point, spread out in a chaotic pattern. This pattern does not typically change from day to day, but over time it often takes on new forms. Patients also commonly notice streaking and flaring distortion around light sources. Some even notice the images moving relative to one another in time with their heart beat.

The predominant optical aberration of the eye as an optical system in keratoconus is the so-called coma.

Causes

Despite considerable research, the etiology of keratoconus remains unknown.  A number of sources suggest that keratoconus likely arises from a number of different factors: genetic, environmental or cellular, any of which may form the trigger for the onset of the disease.

A genetic predisposition to keratoconus has been observed, with the disease running in certain families. The frequency of occurrence in close family members is not clearly defined, though it is known to be considerably higher than that in the general population, and studies have obtained estimates ranging between 6% and 19%.  A high rate of keratoconus incidence is observed in most of the arab countries due to inter-familial marriages. A responsible gene has not been identified: two studies involving isolated, largely homogenetic communities have contrarily mapped putative gene locations to chromosomes 16q and 20q. However, most genetic studies agree on an autosomal dominant model of inheritance. Keratoconus has been associated with atopic diseases, which include asthma, allergies, and eczema, and it is not uncommon for several or all of these diseases to affect one person. A number of studies suggest that vigorous eye rubbing contributes to the progression of keratoconus, and that patients should be discouraged from the practice.

 

Iatrogenic keratoconus has also been observed following LASIK surgery also know as ectasia, caused by removal of excessive stromal bed tissue.

Structural Changes