What is keratoconus?
Keratoconus is a degenerative eye disease that causes the cornea to thin and bulge, creating a cone-like irregular shape. Because the cornea is responsible for refracting most of the light that comes into the eye, any irregularity of the cornea can result in significant visual impairment. Keratoconus most often appears in a person’s late teenage years; although it has been diagnosed in people in their forties and fifties. The eye disease has been estimated to occur in roughly one out of every 2,000 people in the general population. No significant geographical, gender, ethnic, or social pattern has been established, and keratoconus occurs in all parts of the world.
What causes keratoconus?
The exact cause of keratoconus is not known; however, there are many theories on what may trigger this disease. It is important to note that no one theory provides a complete explanation, and it is likely that keratoconus is caused by a combination of things.
It is believed that genetics, the environment, and the endocrine system all play a role in keratoconus:
Genetics: Although keratoconus sometimes affects more than one member of the same family, current research indicates that there is less than a one in ten chance that a blood relative of a keratoconic patient will have keratoconus.
Environmental Factors: Keratoconus may also be associated with overexposure to ultraviolet rays from the sun, excessive eye rubbing, a history of poorly fit contact lenses and chronic eye irritation.
Endocrine System: Another hypothesis is that the endocrine system (which dictates the release of hormones) may be involved, since keratoconus is often first diagnosed in adolescence.
What are the symptoms of keratoconus?
Blurred and distorted vision and frequent eyeglass prescription changes are the first signs of keratoconus. However, blurred and distorted vision occurs as a result of many other types of eye disease, so it is important to visit an experienced eye care professional for diagnosis immediately when noticing any changes in vision. Typically keratoconus occurs in both eyes with one eye more severe than the other. Additional symptoms of keratoconus include:
- Increased light sensitivity
- Difficulty driving at night
- Halo’s and ghosting (especially at night)
- Eye strain
- Headaches and general eye pain
- Eye irritation and excessive eye rubbing
How is keratoconus treated?
Keratoconus is primarily treated with contact lenses because glasses cannot to visually correct the irregular form of the cornea. Surgical treatment options are also available and are typically used when contact lens wear is no longer possible.
Contact Lens Treatment Options
Hybrid Contact Lenses
Hybrid contact lenses are the latest and most advanced option available in contact lenses specifically designed for keratoconus and irregular cornea patients. Using a revolutionary technology, hybrids combine the best of both worlds – the crisp vision of a high-oxygen rigid gas permeable (RGP) contact lens with the all-day comfort and convenience of a soft lens. Hybrids are specifically designed to restore vision to patients with the many types and stages of keratoconus. Because the lens design vaults over the cornea, there’s minimal risk of corneal scarring, making hybrid lenses a healthy treatment option for keratoconus. In addition, the soft skirt of the hybrid design helps to center the contact lens over the visual axis regardless of where the cone is located on the cornea or how large it is, thereby decreasing visual distortions and providing superior vision. The hybrid design also prevents dirt from getting under the lens and will not pop out unexpectedly. No other contact lens available today can provide all of these benefits in a single product.
Rigid Gas Permeable (GSP) Lenses
RGP lenses are made from a rigid material that does not drape over the irregularly shaped cornea, but rather, holds its shape and creates a layer of tears between the cornea and the back surface of the lens. This tear layer neutralizes the irregular shape of the cornea. Consequently, RGPs provide better vision than soft lenses. Unfortunately, for those with keratoconus, RGPs may not provide adequate vision correction. This is because RGP lenses tend to migrate toward the location of the cone, which is usually not on the visual axis, which is near the center of the cornea. For this reason, patients who wear RGPs typically experience problems with inconsistent vision. Furthermore, RGPs are often uncomfortable, inconvenient, allow dirt to be trapped under the lens and may pop out. They can also lead to corneal scarring because they are commonly designed to fit touching the surface of the cone.
Scleral lenses are very large RGP lenses that can provide adequate vision but often require very precise and skilled fitting by your eye care professional. Sclerals occasionally have to be removed and reinserted with fresh saline during the day to keep your vision clear and comfortable.
Soft Contact Lenses
Soft contact lenses are comfortable but are usually unable to visually normalize the irregularities of the keratoconic cornea and therefore do not provide acceptable vision. Soft lenses drape over the irregular corneal surface causing the surface of the lens to assume the same irregular shape as the cornea. This abnormal shape is the reason for blurred and distorted vision. As the cornea becomes more irregular, soft lenses become less effective.
“Piggyback” lenses are RGP’s and soft lenses that are worn at the same time. In some cases, this approach may be more successful than soft or RGP lenses alone, but because of the complexities of handling and care, possible eye health problems due to the decrease in oxygen able to move to the cornea through both lenses, and difficulty with lens centration, success rates are marginal.
Surgical Treatment Options
Patients with keratoconus often ask “Can I have surgery to correct my keratoconus?” There are surgical options that are designed to strengthen, reshape or replace the irregular surface of a keratoconic cornea, and perhaps lessen the impact of keratoconus, but unfortunately none will reverse the progression that has taken place.
The most common surgical treatment options for keratoconus are: Intacs®, corneal collagen crosslinking, corneal transplant or some combination of these procedures.
Intacs are semi-circular plastic implants that are inserted into the middle of the cornea. The intent is to re-shape the cornea to a more normal shape to improve vision. Commonly Intacs do not leave the cornea completely regular in shape, and contacts are still needed for further correction. Intacs are used to improve the patient’s vision, and possibly delay or eliminate the need for a corneal transplant.
Corneal Collagen Cross-linking (CXL)
A new treatment option called corneal collagen cross-linking (CXL) is currently undergoing FDA clinical trials in the United States to determine its safety. With the corneal crosslinking procedure, custom-made riboflavin drops saturate the cornea, which is then activated by ultraviolet-A light. This process has been shown in laboratory and clinical studies to increase the amount of collagen cross-linking and strengthen the cornea
A corneal transplant is a surgery in which a plug of approximately 7.5mm–including the steepest, most irregular part of the cornea–is removed and replaced with corneal tissue from a donor eye. The transplanted tissue is then sutured into place. Lamellar Keratoplasty is a relatively new technique which involves removal of only a partial thickness of the cornea. The theoretical advantage is a lower risk of rejection because the major target for corneal rejection is not transplanted. The resulting cornea is generally flatter and smoother than before, but most often there are still irregularities that are best corrected by a contact lens.
What is a hybrid contact lens?
Hybrid contact lenses are an advanced contact lens option specifically designed for keratoconus and irregular cornea patients. The center of the lens is an RGP and it is surrounded by a soft lens material.
Remember when you had only two choices in contact lenses? “Hard” (RGP) lenses provided GOOD vision, but were often irritating and uncomfortable. Soft lenses offered GOOD comfort, but couldn’t correct your vision problems. Now, a technological breakthrough makes having to compromise a thing of the past. Hybrid contact lenses offer all the benefits of RGP and soft contact lenses without any of the disadvantages for an overall GREAT contact lens experience. Using a revolutionary technology, hybrids combine the best of both worlds – the crisp vision of a high-oxygen rigid gas permeable (RGP) contact lens with the all-day comfort and convenience of a soft lens. Hybrids are specifically designed to restore vision to patients with the many types and stages of keratoconus. Because the lens design vaults over the cornea, there’s minimal risk of corneal scarring, making hybrid lenses a healthy treatment option for keratoconus. In addition, the soft skirt of the hybrid design centers the contact lens more closely over the visual axis regardless of where the cone is located on the cornea or how large it is, decreasing visual distortions and providing superior vision. The hybrid design also prevents dirt from getting under the lens and will not pop out. No other contact lens available today can provide all of these benefits in a single product.