The cornea is the clear, transparent front covering which admits light and begins the refractive process. It is this clear convex cornea which bends (refracts) a ray of light and slows it down. It also shrinks the light to a manageable size (a little smaller than a one rupee coin). It is this front covering of the eye that is affected in keratoconus.
What is keratoconus?
Keratoconus is a degenerative noninflammatory disorder of the eye in which structural changes within the cornea cause it to thin and change to a more conical shape than its normal gradual curve. It derives the name from (kerato – cornea and konus – cone).
How frequent is this disease?
Keratoconus is the most common degenerative disease of the cornea. The incidence is believed to vary from 1 in 2000 to 1 in 1, 00,000 in different regions of the world. Though there are no exact figures for our country, most experts believe it to range between 1 in 2000 to 1 in 5000 population. You are not the only one affected by this problem. Clear Vision Eye Center itself handles hundreds of such eyes every year.
When does it usually present?
Keratoconus is usually seen from early teens to the late twenties. It can present as early as eleven to twelve years of age. It may progress and achieve its most severe state in the age group of twenties or thirties. Does keratoconus affect both eyes? Keratoconus is normally seen affecting both eyes, although the distortion is usually asymmetric and is rarely completely identical in both corneas.
Unilateral cases tend to be uncommon, and may in fact be very rare if a very mild condition in the better eye is simply below the limit of clinical detection. It is common for keratoconus to be diagnosed first in one eye and not until later in the other.
What causes keratoconus?
The causes of keratoconus are still unknown despite our long experience with it. There has been no shortage of speculation or study and numerous theories have been proposed. One scientific view is that keratoconus is developmental (i.e., genetic) in origin. This suggests that it is the consequence of an abnormality of growth, essentially a congenital defect. Another view is that KC represents a degenerative condition. Still a third view is that KC is secondary to some disease process. A less widely held hypothesis suggests that the endocrine system may be involved. This idea gained credence from the usual appearance of the disease because it is generally first detected at puberty.
Heredity influences in KC are suggested by studies that show that approximately 13% of patients have other family members with the disease.
What are the problems in my vision that suggest keratoconus?
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 defect of the eye. As the disease progresses, vision deteriorates, sometimes rapidly. Vision 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. 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.
As mentioned by Nottingham in his classical treatise on keratoconus written in 1854 (yes, that is how long we have known about keratoconus) “… a candle, when looked at, appears like a number of lights, confusedly running into one another” — Nottingham
In its earliest stages, keratoconus causes slight blurring and distortion of vision and increased sensitivity to glare and light. These symptoms usually first appear in the late teens and early twenties.
The classic symptom of slightly more advanced keratoconus is the perception of multiple ‘ghost’ images, known as monocular polyopia. The above image is an artist’s rendition of the same effect. In keratoconus, surface thinning can create multiple optical zones that individually focus the same image to different areas of the 17 retina, thus creating the additional perceived images. 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.
What is difference between keratoconus and “common” astigmatism and what do the numbers mean?
Astigmatism is a common condition where the curvature of one or more of the optical surfaces of the eye (the cornea and lens surfaces) are more “round” in one direction than the other. In “regular” astigmatism the maximum and minimum powers are aligned at 90 degrees to each other while in “irregular” astigmatism they do not align. An egg is a good example of a surface with “regular astigmatism”. Keratoconus is a degenerative condition where the cornea thins in affected areas. This can lead to astigmatism – often regular at first but becoming increasingly irregular as the disease progresses.
How will my Keratoconus specialist diagnose my problem?
There are a variety of tests that will be used by your eye care practitioner. They range from simple vision test, slit lamp examination, retinoscopy, placido disk evaluation, and the most recent and now the very widely used corneal topography.
The key to early diagnosis still remains high degree of suspicion by the eye care practitioner.
An advanced case is usually readily apparent to the examiner, and can provide for an unambiguous diagnosis prior to more specialized testing. It is the diagnosis of the early that remains a challenge to the specialist.