C3R FAQ

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Learn about keratoconus and its treatment.

 

The Normal Cornea
The eye is like a camera in which lenses focus the picture on a light sensitive film. In the human eye, the transparent cornea and lens focus light on the retina, which changes it into electrical signals, which are then transmitted to the brain by the optic nerve to be perceived as images.

 

The cornea is the front transparent window of the eye and forms the outermost one-sixth of the eyeball. It is lamellar in nature (like plywood) and is made up of 5 layers, each of which has a definite function. In order to be effective it must remain transparent. Freezing, heating, molding, lathing, tattooing, excising, incising and transplanting are all means by which the delicate and sensitive cornea has been altered for optical, therapeutic and cosmetic purposes. Due to absence of blood vessels in the cornea, much of its oxygen requirement comes from atmospheric oxygen dissolved in the tear film. When the eyelids are closed, oxygen enters the cornea from the superficial conjunctival vessels. Nutrients needed for the cornea pass into it by diffusion. Hence, carbon dioxide and waste products are also removed across the tear film. Hence, any deficiency of the tear film will directly or indirectly affect the cornea.

 

What is Keratoconus?
Normally the cornea is nearly spherically shaped thus allowing light to be focused clearly on the back of the eye (retina). However in a condition called Keratoconus, the cornea begins to thin, and this allows the normal pressure of the eye to make the cornea bulge forward taking on a cone-shape. As the cornea gradually becomes more cone-shaped, the vision blurs and becomes distorted due to a high degree of astigmatism. Initially vision may be correctable with spectacles, but as the condition progresses, and the cornea becomes more irregular causing distorted vision, spectacles become less effective. In such a situation, contact lenses not only provide better vision, but also help to retard the progress of the disorder. A rigid contact lens (RGP / "semi-soft" contact lenses) must be used, so that it can hold its shape, as a soft lens would simply mould to the existing shape and thus not allow complete correction of the problem. Sometimes the patient is fitted with soft lenses (for comfort), over which semi-soft lenses are fitted ("piggy-back" lenses).

 

Fitting contact lenses for keratoconus requires expertise. Well-fitting contact lenses dramatically improves such a patient's vision to nearly that of a normal person's, and significantly improves his or her quality of life. Any excessive pressure of a poorly fitting lens on the cone apex can cause permanent scarring within months or years (This scarring can also occur naturally). For this reason it is important for regular follow-up visits to be made so that any corneal changes that have occurred can be compensated for in the design of a new lens. It is quite common for patients to be refitted at irregular intervals as the condition progresses. Rarely, scarring is so severe that a corneal graft (transplant) is necessary


A recent promising treatment modality for keratoconus is C3R (Corneal Collagen Cross-linking

 

What is Corneal Collagen Cross-linking (C3R)?
Cross Linking of Cornea Collagen (C3R) is a process to increase the mechanical stability of corneal tissue. The aim of this treatment is to create additional chemical bonds inside the corneal stroma by means of a highly localized photo polymerization.


The indications for cross linking today are corneal ectasia the disorders such as keratoconus and pellucid marginal degeneration, iatrogenic keratectasia after refractive lamellar surgery and corneal melting that is not responding to conventional therapy.

 

The History of Corneal Cross-linking
The procedure was developed from 1993 till 1997 by Prof. Theo seiler and Prof. Eberhard Spoeri at the University of Dresden, Germany. The first patients were treated in 1998. Today corneal cross-linking is performed in more than 300 centers around the world. Corneal Cross-linking has the potential to become the standard treatment for keratoconus thus preventing the need for penetrating keratoplasty!

 

The Principle of C3R
Photo-polymerization using UV-light was found to be the most promising technique to achieve cross-links in connective tissue. Photo-polymerization is activated by means of a non-toxic and soluble photomediator and a wavelength which is absorbed strongly enough to protect deeper layers of the eye (riboflavin-UVA technique).

 

UV-A radiation with concomitant administration of riboflavin solution leads to physical cross linking of the corneal collagen fibers.
Thus progressive corneal thinning is slowed down or even stopped and the Bio-mechanical strength of corneal tissue is improved.

 

The Device for C3R
For C3R we need riboflavin dye and a special device called cross-linker. Cross linker is a device to deliver UV-A light of specific wavelength of 365 nm , at controlled energy level of 3 mW/cm.sq.

 

The C3R Procedure
After removal of the corneal epithelium, riboflavin solution is instilled for 30 minutes on to the cornea. Then the corneal penetration of this is checked by establishing that the anterior chamber is slightly yellow. Pachymetry is performed to make sure that minimum corneal thickness is maintained.

 

UV-A radiation starts under continued administration of Riboflavin Solution. After 30 minutes of radiation treatment is finished and the patient receives post-operative treatment like after a PRK procedure. A bandage contact lens is inserted in the operated eye and the patient is administered oral and topical antibiotics, steroids, anti-inflammatory medication as well as lubricant eye drops.

 

Clinical Experience with C3R

  • Today, more than 1,400 eyes have been cross-linked world wide in controlled clinical studies with a follow up to 5 years.
  • Clinical studies have shown a significant increase in best corrected visual acuity (BCVA) in more than 85% of the treated eyes.
  • Six months after corneal cross-linking the refractive cylinder was reduced in over 80% of the eyes.
  • The steepest K-value was usually decreased by 1 diopter and the percentage of eyes that had a clinical relevant reduction exceeds 86%.

 

Safety of C3R
Corneal cross-linking is considered to be a safe procedure, provided the recommended safeguards are observed. Up until today no sight threatening side effects have been reported.