Keratoconus is an eye condition
affecting about 1 in every 2000 people. This eye disorder results in the progressive thinning of the cornea, which leads to a cone shape of the eye. It is commonly referred to as causing irregular
astigmatism. The cone-shaped cornea deflects light irregularly as it enters the eye causing distorted vision. Corneal shapes come in 3 basic forms: spherical, regular astigmatism, and irregular astigmatism. The analogy of each is as follows: a spherical cornea is like one side of a soccer ball; a regular astigmatism-shaped cornea is like one side of a football; and an irregular astigmatism-shaped cornea such as is found with keratoconus is like one side of a warped football.
Patients suffering from keratoconus often complain of blurry vision, double or shadowed vision. They often have nearsightedness, astigmatism, and will complain of light sensitivity (photosensitivity). In more severe cases, scarring within the cornea develops, further reducing visual acuity. Another common symptom of keratoconus is ‘ghosting’ of images, also known as monocular polyopia. When there is a high contrast target (e.g. the headlight of an oncoming vehicle as seen at night) a person that has keratoconus may see the headlight in a chaotic pattern, as well as streaking emanating from the light source. This is referred to as starburst and is a form of disabling glare.
The cause of keratoconus is unknown, but there are genetic, environmental, and hormonal factors that appear to contribute to its development. For example, a family history of the condition, allergies, excessive rubbing of the eyes and overexposure to UV light.
Diagnosing keratoconus begins like any other eye condition – with an assessment by an optometrist. They will listen to your symptoms, discuss your medical history, other ocular diseases or injuries, family history, and test your visual acuity and perform a refraction, then examine the structure and health of your eyes. The early stages of keratoconus may be no different than any other refractive error, mostly blurred vision. As the condition progresses, it’s easier to diagnose the condition as keratoconus.
If keratoconus is suspected, the optometrist can use a keratometer or topographer to measure the curvature and overall shape of the cornea, as well as measuring the thickness of the corneal tissue with a pachymeter. Another method to aid in the diagnosis is retinoscopy, which helps assess the way the eye focuses or bends light. The reflection of light thru the eye and off the retina is observed as the examiner tilts the light source. This can help with diagnosing keratoconus as the examiner will see what is called a scissor’s reflex of light reflected from the eye within the patient’s pupil if keratoconus is present.
A very important component for diagnosing keratoconus is a slit lamp examination. A slit lamp is a microscope that allows us to see the fine structures of the eye. Sometimes, a ring of yellow-brown or olive-green pigmentation, known as a Fleischer’s ring, can be observed in a keratoconic eye. An examiner may also be able to view Vogt’s striae, which are fine stress lines in the posterior of the cornea caused by the stretching and thinning of the corneal tissue that occurs with keratoconus. A keratoconus eye usually has posterior thinning and protruding of the cornea, with a central thickness often less than 450 microns. Most healthy corneas average a central corneal thickness of 540 microns.
A keratoscope can provide a non-invasive visualization of the surface of the cornea by projecting concentric rings of light onto the cornea. This way, the examiner can see the corneal shape with an elevation or curvature map and any distortions from scarring to diagnose keratoconus.
Once keratoconus is diagnosed, the prognosis differs between patients. It typically begins with mild astigmatism and myopia around puberty and as the condition progresses, it can lead to rapid vision loss or frequent fluctuations in prescription. It is typically diagnosed in the late teens or early 20s, but this condition can become present or progress at any age.
Keratoconus does not typically result in blindness or severe vision loss. A patient’s vision can fluctuate greatly over a period as short as a few months, so prescription changes may be frequent. Some patients may be more stable, experiencing a steady vision loss. The condition will progress for a period of 10 to 20 years and then usually ceases in a person’s 30s or 40s. About 10% will go on to need a corneal transplant. Corneal cross linking is a treatment aimed to improve a patient’s long term prognosis. It is a procedure that uses riboflavin (vitamin B2) and ultraviolet light to cause a structural change in the corneal crosslinks within the stroma of the cornea. The end goals of this procedure, which takes months to manifest, are: a flattening or reduction in the steepness of the cornea; a strengthening of the cornea itself; and when combined with laser reshaping, a reduction in the amount of corneal refractive astigmatism. A downside to this procedure is the resulting corneal haze that follows, which can also limit a patient’s best corrected acuity. Currently, corneal cross-linking costs around $200 per eye treated for patient’s with OHIP coverage.
Only in severe cases will the cornea become so damaged from stretching that vision loss will be more drastic. In these situations, a corneal transplant may be required to correct the substantial vision loss. However, for those suffering from keratoconus, this is not typical. The condition will often simply result in vision fluctuations and ghost images that can be corrected with contact lenses.
Keratoconus Treatment – Contact Lenses
In the early stages of keratoconus, glasses or soft contact lenses are used to correct vision. As the condition progresses, these solutions will not be enough to correct a patient’s vision.
Rigid, gas-permeable contact lenses are the most common keratoconus treatment. Because they are rigid, they allow the eye to use tear fluid to fill the gap between the irregular corneal surface and the smooth contact lens surface. This creates the effect of a smooth cornea and reduces the effects of a cone shaped cornea.
There are other options for keratoconus contact lenses. Hybrid lenses are also available which are rigid in the centre and soft around the outside of the lens, however, these are still in development and aren’t successful for every patient. Scleral lenses are larger, rigid lenses that cover more of the eye’s surface and offer greater stability for the cornea. These are often used in people with mobility restraints, such as the elderly. Lastly, a combination of lenses is successful for some patients. Wearing rigid lenses over soft lenses, both with a measure of vision correction, can provide better vision correction for some.
None of these keratoconus treatments stop the condition from progressing; they simply provide the necessary vision correction. The condition typically stops deteriorating 10 to 20 years after it begins.
Contact Us Today!
If you’ve been suffering from rapidly changing vision or are unsatisfied with your current vision correction, contact the eye care office of Dr. Sciberras. He can diagnose keratoconus and find the right treatment options that suit your comfort level and stage of keratoconus.
Watch these animations on keratoconus to learn more. BEGIN