In keratoconus, the cornea gradually becomes thinner and conical in shape. The thinnest aspect of the cornea is usually in the middle or slightly below the middle portion of the cornea. Keratoconus is usually progressive, with the cornea becoming more steep and irregular over time. With early or mild keratoconus, patients may have normal vision with glasses. As the disorder advances, vision may become distorted.
The vision may be corrected with a variety of methods that will be discussed below.
Note the distorted pattern of the rings
Etiology and Prevalence
Doctors at EDOW treat keratoconus patients on a daily basis. Keratoconus has been reported to affect approximately 1 in 5, 000 to 10,000 persons. Onset is usually during the late teenage years; however, it has occurred in children as young as 6 years of age. Keratoconus rarely develops after the age of 30. It affects men and women equally. Keratoconus is present in both eyes in over 90% of cases; however the onset is not always at the same time or to the same magnitude.
Keratoconus is usually progressive from the late teenage years until the mid thirties. Then, in approximately 75% of cases, the disease becomes stable. During the active stage, changes may be rapid. The thinning process is non-inflammatory; therefore, patients do not feel any pain or discomfort.
The cause of keratoconus is unknown. It has been found to be familial (meaning it is more common in certain families), but the exact mode of genetic transmission is unknown. It is associated with certain medical conditions such as atopy, Erlos-Danlos, and Downs Syndrome. It may also be associated with long-term use of rigid contact lens wear.
Keratoconus has no known cure. Fortunately, almost all patients with keratoconus live a normal, active life due to the variety of treatments at their disposal. See below to learn more about the present options.
The doctors at EDOW have advanced diagnostic equipment
to assist in the diagnosis and treatment of keratoconus. In
moderate or advanced keratoconus, making the diagnosis
is fairly simple due to the classic findings on physical examination with a slit lamp. These findings include the following:
Fleisher ring: this ring is a yellow-brown to olive-green ring of pigment which surrounds the base of the cone. It is formed from the iron in the tear film.
Vogt Striae: Small stress lines on the inner portion of the cornea.
Corneal thinning. In advanced cases, the thinning of the central cornea can be seen on examination.
Corneal scarring – in advanced keratoconus – the cornea develops central scarring.
Diagnosing keratoconus in its early stages is more difficult. It requires a thorough history and examination. Patients with undetected early keratoconus will often visit a variety of eye doctors over a short period of time. They often receive several different spectacle prescriptions that do not provide satisfactory vision. The irregular shape of the cornea causes refractions to be variable and inconsistent because the image with any lens prescription is distorted. Keratoconus patients often report (monocular diplopia) ghost images and distortions rather than blur at both distance and near vision.
A variety of diagnostic tests can be performed to assist in the diagnosis of keratoconus.
Computerized corneal topography can provide an overview of the cornea and can show the relative steepness of any corneal area. EDOW has the most advanced topography units, an Orbscan. This unit can simultaneously measure the curvature and thickness of the cornea over the entire surface.
Photograph of normal cornea
Topography of mild keratoconus
Topography of intermediate keratoconus
Topography of advanced keratoconus
In mild keratoconus, wavefront analysis can be determined to quantify the amount of aberration caused by irregular astigmatism.
Glasses: In mild or early keratoconus, glasses can be used for vision correction. Unfortunately, as keratoconus progresses, the irregular shape of the cornea cannot be corrected with glasses.
Soft contact lenses may be worn with early or mild keratoconus. Since soft contact lenses conform to the shape of the cornea. They are not able to eliminate visual distortion created by the irregular shape. For this reason, patients usually require the use of a rigid contact lens.
Rigid contact lenses (hard and gas permeable) create a stable surface upon which light can be focused into the eye. With mild or moderate keratoconus, a rigid lens can reduce or eliminate the distortion created by the abnormal corneal curvature. The optometrists at EDOW can fit patients with rigid contact lenses. They are experts in this field and receive referrals from patients throughout the world.
A variety of surgical procedures are available for patients with keratoconus. Penetrating keratoplasty is the most common. Recently, less invasive procedures, such as Intacs, have been developed.
Penetrating keratoplasty: In this procedure, the central area of the cornea is excised and a full-thickness corneal button is sutured into the recipient. For a complete description, see the corneal surgery section of this website.
Lamellar keratoplasty: A partial thickness portion of the cornea is excised and a partial thickness donor corneal button is sutured into the recipient transplant.
Intacs: Two arc shaped segments of inert plastic are inserted into the peripheral (outer) cornea. These segments add volume to the thinned cornea. This flattens the steep curvature and educes the irregular shape. For a complete description see the corneal surgery section of this website.
Phototherapeutic Keratectomy (PTK): Excimer laser procedures can remove superficial corneal scars. PTK is often helpful in rigid contact lens wearers who have developed a central plaque-like scar. These scars can reduce vision and irritate the cornea via mechanical rubbing.