What is Keratoconus?
Keratoconus is a slow, progressive eye disease in which the normally round, dome shaped cornea (the clear outer front portion of the eye) thins and begins to bulge into a cone-like shape. This cone shape is irregular, bending light as it enters the eye. Since the cornea is responsible for refracting most of the light coming into your eye, an irregular cornea causes blurred vision.
How does Keratoconus develop?
The cornea, the outermost layer of the eye, is usually a regular round shape. If you develop keratoconus, the middle of your cornea becomes thinner and gradually bulges outwards. Eventually, the cornea forms a rounded cone shape, producing distorted vision and short-sightedness. Both eyes are usually affected by keratoconus but not always equally.
The astigmatism and short-sightedness caused by keratoconus gets worse over time, as the cornea continues to change shape. Swelling of the stroma can be painful, and it can cause corneal scarring as well as a reduction in vision.
Keratoconus is an eye disease of young people; symptoms usually start at around puberty and progress through the teens and 20s, with the greatest impact experienced by people aged 21-30. Some people experience several years where their cornea remains stable, others deteriorate quickly. Prompt treatment can delay the progression of keratoconus but when the condition has deteriorated significantly the only treatment that can restore reasonable visual acuity is a corneal transplant. This happens in about 20% of people with keratoconus.
How does Keratoconus Progress?
In the early stages of keratoconus, the disease can cause some blurring and distorted vision. People with keratoconus may also begin noticing an increased sensitivity to light. It is common for these symptoms to first appear in the late teens and early twenties. Keratoconus can progress for a couple decades and then slow or stabilize. Early onset keratoconus appears to indicate a greater risk of the disease being more severe later in life. It is also possible for each eye to be affected differently.
Symptoms of Keratoconus
In the early stage, keratoconus symptoms can include:
- mild blurring of vision
- slightly distorted vision, where straight lines look bent or wavy
- increased sensitivity to light and glare
- eye redness or swelling
What Causes Keratoconus?
New research suggests the weakening of the corneal tissue that leads to keratoconus may be due to an imbalance of enzymes within the cornea. This imbalance makes the cornea more susceptible to oxidative damage from compounds called free radicals, causing it to weaken and bulge forward.
Risk factors for oxidative damage and weakening of the cornea include a genetic predisposition, explaining why keratoconus often affects more than one member of the same family.
Keratoconus also is associated with overexposure to ultraviolet rays from the sun, excessive eye rubbing, a history of poorly fitted contact lenses and chronic eye irritation.
Do not rub your eyes!
With keratoconus, try to avoid rubbing your eyes. This can damage thin corneal tissue and make your symptoms worse.
If you have itchy eyes that cause you to rub, speak to your ophthalmologist about medicines to control your allergies.
Keratoconus Treatment and Management
1. Corneal Crosslinking
Description: Corneal crosslinking halts progression of keratoconus by strengthening the cornea by hardening the covalent connections between corneal collagen fibrils in the stroma.4,7
Who is a Candidate?
- A patient who has been diagnosed with KCN and who you feel is at risk of progression.
- A patient having post-LASIK ectasia who, by diagnosis, has already shown progression.
Benefits of Crosslinking
- Stabilization of progression
- Reduction of ectasia
2. Contact Lenses
Contact lenses, specifically gas permeable contact lenses, provide a great option for clearer vision for those with this condition because the tear film between the rigid contact lens and the cornea masks irregularities on the anterior corneal surface.
3. Corneal Transplants
Who is a good candidate?
- Those with corneal scarring that is interfering with the visual axis.
- Those for whom contact lenses are intolerable or are unable to handle daily lens insertion and removal
Intacs are intracorneal ring segments (ICRS) made of a plastic material called PMMA (polymethyl methacrylate), that are placed in the corneal stroma at about 75% depth (~400 microns).
The goal of Intac segment placement is to normalize and flatten the corneal surface, reducing irregular astigmatism and improving visual acuity with glasses or contact lenses. The improvement in corneal shape may result in better contact lens tolerance.
Those with central corneal thickness greater than or equal to 400 microns, peripheral corneal thickness around 450 microns, and no corneal scarring.
How does it work?
Intac segments do not halt the progression of keratoconus; however, they do have potential to “normalize” the cornea by redistributing the collagen lamellae in the cornea. The lamellae move towards the peripheral intact segments (steepening) and subsequently flatten the central cornea.