Keratoconus

Keratoconus

What is Keratoconus?

Keratoconus, often referred to as “KC,” is a slowly progressive, non-inflammatory eye disease that causes the cornea to thin and bulge out, taking on a cone-shaped appearance. The cornea’s job is to refract light that enters the eye. When people talk about “the windows to the soul,” they are speaking of the cornea.

Because of its important job, abnormalities or injuries to the cornea can significantly affect your vision and impair your ability to perform simple tasks like driving, watching TV, or reading a book. Keratoconus can affect one or both eyes, and it can affect each eye differently. One out of every two thousand people may develop keratoconus. In most cases, it begins to develop during adolescence and young adulthood and slowly progresses over the next decade or two before stabilizing.

Symptoms of Keratoconus

This is a slow, progressive disease. Some people may not notice their cornea changing shape, while other people experience a rapid and obvious change. Besides the cone-shaped appearance of the cornea, symptoms of keratoconus may include:

  • Distorted vision
  • Increased photophobia (light sensitivity)
  • Nearsightedness may develop slowly
  • Irregular astigmatism may develop slowly
  • Blurred vision
  • Need for new eyeglass prescription every time you visit eye doctor

What Causes Keratoconus?

The cause of keratoconus is currently unknown, although some of the suspected causes include:

  • Injuries or damage to the cornea
  • Weakened corneal tissue due to an imbalance of enzymes within the cornea
  • Excessive eye rubbing
  • Chronic eye irritation
  • Poorly fitted contact lenses
  • Heredity

Some researchers believe the imbalance of enzymes within the cornea makes the cornea more prone to oxidative damage from compounds called free radicals, eventually causing the cornea to weaken and bulge out. However, there is currently no reproducible evidence to support this. Keratoconus is believed to be genetically transmitted, and sometimes it will affect more than one member of a family. In fact, 14 percent of all known cases of keratoconus show evidence of genetic transmission.

Diagnosing Keratoconus

If you suspect you have keratoconus, you should consider making an appointment with your eye doctor immediately. Early diagnosis can prevent further damage and vision loss. During the eye exam, your eye doctor will ask you questions about your symptoms and family medical history. You will be given a visual acuity test, possibly with the Snellen chart. A keratometer is used to measure the curvature of your cornea and the extent and axis of the astigmatism. In severe cases, the keratometer may not be enough to make a correct diagnosis. If so, additional diagnostic tests will be employed. These include:

Retinoscopy: This involves focusing a light beam on your retina and observing the “reflex,” which is the reflection as the light beam is tilted back and forth. Your eye doctor looks for a scissor effect, since keratoconus exhibits two bands moving toward and away from each other like the blades of scissors do.

Slit-lamp exam: If keratoconus is suspected during the retinoscopy, this exam will be performed. Slit-lamp exams look for other specific characteristics of keratoconus, such as the Fleischer ring (a yellowish-brownish-greenish pigmentation) in the cornea.

Keratoscope: This technique is non-invasive and checks the surface of the cornea by projecting a series of concentric rings of light onto it.

Corneal topography: An automated instrument is used to project illuminated patterns onto the cornea to determine its topology (the relationship between objects that share the same surface or border). This exam works best when keratoconus is in its early stages, as it shows any distortions or scarring on the cornea.

Keratoconus Treatment

Eyeglasses and soft contact lenses are the usual treatment for those with mild keratoconus, but this disease is progressive and inevitably thins the cornea, giving it an increasingly irregular shape. Eventually eyeglasses and soft contact lenses are no longer sufficient. Severe cases of keratoconus need treatment such as:

Gas permeable contact lenses: Also known as RGP or GP lenses, rigid gas permeable contact lenses are most commonly used due to their rigidity, which improves vision by changing the irregular cone shape into a smooth, refracting surface. These types of lenses are uncomfortable at first, but most people adjust within a week or two. These lenses are not permanent, since the progressive nature of the disease requires continual prescription updates. Frequent visits to the eye doctor should be expected.

Piggyback contact lenses: Due to the discomfort caused by gas permeable lenses, some eye doctors use two different types of contact lenses on the same eye; a method known as piggybacking. Typically, one lens is made of a soft material, such as silicone hydrogel, with an RGP lens over the top of it. The soft lens acts as a cushion to the harder lens. Your eye doctor will closely monitor the fitting of the two lenses to ensure that oxygen reaches the surface of your eye, although today’s contact lenses — both soft and hard — are sufficiently oxygen-permeable for safe use.

Scleral and semi-scleral contact lenses: These gas-permeable lenses have larger diameters, enabling the edges of the lenses to rest on the sclera (the white part of your eye). Semi-scleral lenses are a smaller version, but they still rest on the sclera. Many people like this contact lens due to its stability, comfort, and the lack of pressure applied to the eye’s surface.

Corneal inserts or Intacs: These tiny arc-like plastic inserts are placed in the middle of the cornea in order to reshape it. Typically, Intacs are used when other treatment options such as contact lenses and eyeglasses fail to improve vision. The inserts are removable and exchangeable, and the surgical procedure lasts only ten minutes. If keratoconus continues to progress after the Intacs are inserted, a corneal transplant may be necessary.

Corneal cross-linking: This procedure involves strengthening the corneal tissue to halt the bulging of the eye’s surface. This method was introduced in the United States in 2008, and is also known as CXL. During the procedure, the epithelium (the outer portion of the cornea) is removed, riboflavin (a B vitamin) is applied, and the patient’s eye is put under a specialized lamp, which emits UV light that activates and strengthens the cornea. Another method, known as transepithelial corneal cross-linking, is employed in a similar fashion, only the corneal surface is left intact. Many experts believe this method reduces the need for corneal transplants and prevents keratoconus-like complications after vision correction surgery such as LASIK.

Corneal transplant: When all else fails, corneal transplants are performed. Unfortunately, some people cannot tolerate rigid contact lenses, or they reach a point where all non-surgical treatment options have been exhausted. Also known as a penetrating keratoplasty, PK, or PKP, corneal transplants involve removing the cornea and replacing it with a healthy cornea from a donor in hopes of restoring vision and preventing blindness. General anesthesia is used before this procedure. After the transplant is complete, the ophthalmologist will use sutures to hold the transplanted cornea in place. The sutures are removed after healing is complete, which is usually three to four weeks. In most cases, eyeglasses and contact lenses are needed after surgery.

In any case of keratoconus, frequent check-ups and changes in prescription are needed to achieve good vision and comfort. Follow your eye doctor’s instructions and contact your eye doctor immediately for a check-up if you experience scratchiness, tearing, discharge, or irritation. If symptoms develop after treatment has begun, then your eyes are ready for a new prescription.

Complications of Keratoconus

Complications of keratoconus may include:

  • Vision loss that may lead to blindness
  • A change in the shape of the eye
  • Additional eye problems such as astigmatism

Complications of a corneal transplant may include:

  • Surgical wound infection
  • Rejection of the transplant
  • Secondary glaucoma

Preventing Keratoconus

Keratoconus is not preventable, but those who are diagnosed with it can do things to ensure that their eyes function to the best of their ability and to prevent the disease from worsening:

  • Follow your eye doctor’s instructions at all times.
  • Watch for changes in your vision, and report any new symptoms to your eye doctor as soon as possible.
  • Do not use medicines not prescribed to you. If a family member or friend has the same disease, do not use their medication, as their needs more than likely differ from yours.
  • Do not treat yourself with over-the-counter eye drops or medications.
  • Avoid using make-up near the eyes.
  • If a substance irritates the eyes, discontinue using it.
  • Protect your eyes with goggles when swimming and during athletic activities.
  • Resolve any allergy issues before allergy season begins.

Talking to Your Eye Doctor

Here are some questions to ask your eye care professional about keratoconus:

  • How severe is my condition?
  • Are there nutritional supplements that will benefit me?
  • Which treatment options are available for me?
  • If new symptoms develop, how long should I wait before contacting you?
  • Which diagnostic tests can I expect during each visit?
  • Now that I have been diagnosed with keratoconus, how often will I need to see you?

What’s New?

According to the National Keratoconus Foundation, keratoconus research is moving forward in many areas. Scientists are trying to determine the cause of keratoconus by examining the ways in which affected corneas differ from normal corneas.

Another exciting development in the treatment of keratoconus: Wavefront Guided Soft Contact Lenses, or WGSLs. These are similar to conventional soft contact lenses. The difference is that researchers are able to customize WGSLs to patients’ individual needs. WGSLs are created using wavefront sensing, which can correct the highly aberrated optics in the eye seen in keratoconus — something conventional soft contact lenses cannot do. Funded by the National Eye Institute, the Visual Optics Institute at the University of Houston, College of Optometry is now conducting studies on patients with keratoconus. These lenses are still being researched and are not yet available.

Did you know … adult stem cells exist at the edges of the cornea, so research is now being conducted to find ways to use them to grow new corneal tissue.

References:
  • The National Keratoconus Foundation, 2011, Wavefront Sensing: An Exciting Technology http://www.nkcf.org/en/research/research-update/128-wavefront-sensing-an-exciting-technology.html
  • J. Anshel “Smart Medicine for Your Eyes” (SquareOne Publishers, 2011) 251-252
  • Keratoconus.com http://www.keratoconus.com/
This article was last updated on 07/2014