What is Keratoconus?

Catherine McCarthy

Author

Catherine McCarthy

B.Optom(RAU)
M.C.Optom(UK)

In this article we describe the keratoconus condition, what it is, how it affects you and how it can be treated.

Keratoconus is an eye condition that affects the curvature of the cornea .The cornea progressively thins out and starts to bulge out to form a cone.

Where the cornea is and what is it made up of?

The cornea forms the front part of the eye and is over the Iris, which is the pigmented part of your eye that gives your eye colour. It is a clear surface that directs light through the lens to the retina to form a clear image.

This is a cross-section of an illustrated eyeball. The cornea is in the front of the eye.

The cornea is made up of 5 Differing cell layers, as illustrated and labeled below. The epithelium is the first layer of the cornea.

The stroma which occupies about 90% of the total corneal thickness is composed of collagen fibrils, keratocytes and extracellular ground substances. Collagen components constitute more than 70% of the dry weight of cornea. Collagen fibrils with uniform 25- to 35-nm diameter are arranged in flat bundles called lamellae.

What Causes Keratoconus?

Many genetic diseases are associated with keratoconus, such as Down’s syndrome, Marfan’s Syndrome and Ehlers-Danlos Syndrome to name a few.

Based on current scientific research about 7 to 10 percent of Healthy Keratoconic patients have a family history of keratoconus. However some researchers believe this percentage is higher and that family members with a suscepablity to the condition may have not been exposed to ceratin stressors that would have triggered Keratoconus.

Such stressors are explained in the oxidative stress theory. Oxidative stress is essentially an imbalance between the production of free radicals and the ability of the body to get rid of theses harmful radicals with antioxidants. Free radicals in accumulation can cause cancers and in the case of the cornea, a degradation of the collagen fibrils which maintains the structural shape of the cornea. Researchers believe that people genetically susceptible to Keratoconus cannot cope with oxidative stress as effectively. The hypothesis essentially states that there is a genetic predisposition that requires a “second hit” or environmental event to elicit progressive disease in keratoconus.

Examples of oxidative stressors /”The Second Hit’ include:

  • High Exposure to Ultra Violet Light
  • Vigorous eye rubbing due to itching. By rubbing the eye continuously and with pressure you can change the curvature and even scar the cornea.Conditions such seasonal allergic conjunctivitis, contact lens associated irritation/allergy and various atopic diseases (such as hay fever, eczema, asthma and food allergies) can cause moderate to severe eye itchiness.
  • Poorly fitted Rigid Gas Permeable lenses (RGP).If a RGP contact lens is fitted incorrectly; it can mechanically alter the curvature of the cornea. This may be more commonly seen with patients who do not have their contact lens fit regularly checked and their lenses replaced as specified by their optometrist.
  • Laser eye Surgery on corneas that are too thin to have the procedure done on can result in Keratoconus.It is important that a thorough examination be done by the eye surgeon to establish that you are a good candidate for laser eye surgery. This includes taking a detailed ocular family history.

Based upon this evidence, one can speculate that keratoconus patients should minimize their exposure to oxidative stress. Protective steps should include wearing ultraviolet (UV) protection (in the contact lenses and/or sunglasses), minimizing the mechanical trauma (eye rubbing, poorly fit contact lenses) and keeping eyes comfortable with artificial tears, non-steroidal anti-inflammatory drugs and/or allergy medications.

Age and Ethnicity:

Keratoconus classically starts in puberty and can progress till the third and fourth decade of live however this can vary with each individual. There may be a hormonal influence because it typically coincides with puberty and it has shown to advance during pregnancy.

There is also a link with ethnicity and hotter countries. Asian communities show a high incidence, particularly Northern Pakistan. Research suggests this may be due to traditional marriages to first cousins and therefore shows a further genetic link in this progressive disease. The link to hotter countries may be due to the higher UV exposure (An oxidative stressor)

Symptoms of Keratoconus:

  • Blurred vision
  • Radically changing spectacle prescription
  • Increased light sensitivity
  • A halo around lights and ghosting (especially at night)
  • Eye strain
  • Headaches and general eye pain
  • Eye irritation
  • Excessive eye rubbing

Treatment options for Keratoconus:

In the early stages of Kertoconus the vision can be corrected with spectacles and as the vision becomes poorer with the spectacles then contact lenses can be fitted. The idea is to create a new smooth surface for the light to enter the eye, i.e. an artificial cornea in the form of a keratoconus contact lens. If you think you suffer from Kertoconus, contact us today to schedule an optometrist appointment.

There are a variety of Keratoconus Contact lenses, these include the following:

  • Kerasoft Lenses
  • Keratoconus Rigid Gas Permeable lenses(RGP)
  • A combination of a conventional soft contact lens with a RGP Lens. Known as a piggy back system.
  • Hybrid Lenses; which are hard in the centre and have a soft skirting
  • Scleral Lenses: which are large diameter lenses that vault the cornea

Surgical Treatments

Corneal Cross Linking (CXL)

In the early to moderate stages of keratoconus, a patient can be referred by his/her optometrist to a corneal specialist for Corneal Cross Linking (CXL). This technique involves Riboflavin eye drops being placed on the cornea and activated by an ultraviolet light lamp source. Riboflavin has been shown to increase collagen crosslinking in the cornea and thus increasing the overall strength of the cornea and flattening it. By CXL we hope to halt or slow down the progression of keratoconus, his technique is not a cure. The procedure lasts approximately 30 minutes and you’ll need 5 to 7days off work for the swelling to come down. The vision can be blurry for a few weeks and increasingly improves over several months.

In certain cases were the keratoconus is very stable, the optometrist may choose to monitor and treat with eye drops and/or Contact lenses and spectacles.

Kera-Rings and Intacs

Kera-rings and intacs fall under intra-corneal rings are made of a plastic and come in different widths and lengths. The rings are implanted in the cornea and the procedure is reversible. The ring flattens the cornea and in doing so reduces the astigmatism and myopia (Short-sighted vision) and slows further progression.

This photo shows 2 intra-corneal rings

Corneal Transplant

In severe cases where the cornea is scarred, the vision is very poor or no contact lens and spectacles assist with sight, then a corneal transplant is done.

Older techniques required that the entire cornea be removed and replaced with a full-thickness cornea from a donor. Now days, a partial thickness technique is preferred and is called a lamellar corneal transplant or DALK (Deep Anterior Lamellar Keratoplasy). This technique reduces rejection rates of the new cornea and aids in better healing and overall visual results. You can expect to take 2 weeks off work and to avoid heavy physical activity for 8 weeks or more. A corneal transplant takes months to fully heal.

CATHERINE ROSEWALL-MCCARTHY

B.Optom(RAU) M.C.Optom(UK)

What is Keratoconus?

If you have further questions about this topic, or feel that you need to discuss your personal situation with a professional optometrist, please contact us so we can assist you further.

LARA JOSEPH

B.Optom(RAU)