Corneal Collagen Cross-Linking With Riboflavin - What It Does
The cornea, the clear dome-shaped window on the front of the eye, consists of 5 different layers of tissue. The stroma accounts for 90% of the thickness of the cornea and is made up of about 300 layers of collagen fibrils that run parallel to each other in a “jelly-like” substance made up of proteoglycans. It was originally thought that Corneal Collagen Cross Linking with Riboflavin (“KXL”) strengthened or increased the bonds between the collagen fibres. According to the latest research, it is now believed that it may actually be a stiffening of the “jelly-like” proteoglycans, similar to adding pectin to jelly to make it stiffer. The effect is that the structural strength of the cornea is increased.
Why It is Used
For therapeutic use, there are several corneal conditions that KXL is being used for. Keratoconus, Pellucid Marginal Degeneration and post-laser refractive surgery ectasia are the most common conditions that are treated with KXL. Keratoconus is a progressive corneal disease whereby the central cornea gradually bulges forward in a cone shape, with corneal thinning and distortion of vision. Pellucid Marginal Degeneration involves thinning and bulging of the inferior portion of the cornea. Post-laser refractive surgery ectasia is a bulging forward of the thinned, central portion of the cornea after Myopic laser refractive surgery correction.
For prophylactic use, virtually any patient can be treated with cross-linking to reduce the chance of future development of the above conditions, especially patients with thinner than normal corneas, irregular corneal astigmatism, asymmetry on corneal topography, against-the-rule astigmatism or steeper than normal corneas.
Collagen Cross-linking has been used for many years in the field of Dentistry. Corneal Collagen Cross-Linking with Riboflavin was first used in 1998 to treat Keratoconus. The use of this procedure has gradually increased, with 400+ centres around the world now performing this procedure. The procedure has been refined over the years, with adjustments to the Riboflavin soak time and to the UVA light exposure time and energy levels. Corneal Collagen Cross Linking with Riboflavin is also known as CXL, CCR, CCL, C3-R and KXL. The Ophthalmic community is starting to see the benefits of prophylactic (preventative) treatment using Cross-linking and this procedure is now starting to be offered as a standalone procedure or in conjunction with corneal laser refractive surgery (PRK and LASIK). There are currently 3 available systems that provide the UVA light source. The UV-X™ Illumination System is the most widely used system currently. The Avedro KXL Accelerated Cross-Linking system is newer and has not yet been approved in the US by the FDA. The Avedro KXL Accelerated Corneal Collagen Cross-Linking system has been approved in Europe and by Health Canada and other countries. We do not require FDA approval to use the device as long as it has been approved by Health Canada.
The 5 layers of the cornea include the Epithelium (the outer corneal surface layer), Bowman’s membrane, stroma, Descemet’s membrane and endothelium. The objective is to apply a solution of Riboflavin to the stromal layer and then apply UVA light. Current Riboflavin solutions are typically not able to penetrate the epithelium so the epithelium needs to be removed, or the Riboflavin solution can be applied to the stromal bed after an IntraLASIK flap has been created and lifted or when relifting a previously created IntraLASIK or LASIK flap. There are new Riboflavin solutions being developed that can penetrate the epithelium and this procedure is called Transepithelial Corneal Collagen Cross-linking. With the most commonly used system, the UV-X™ Illumination System, there is a 30 minute Riboflavin soak time and then typically 30 minutes of UVA exposure. The new IROC UV-X™ 2000 Illumination System uses a 30 minute Riboflavin soak time and then typically 10-12 minutes of UVA exposure. With Gimbel Eye Centre’s Avedro KXL® Accelerated Cross-Linking system, there is a 3-5 minute soak time and then typically 3 minutes of UVA exposure. The Avedro system uses higher power for a shorter time to give a similar amount of Energy applied to the cornea as the IROC system. If the corneal cross-linking is done at the time of PRK or IntraLASIK, the Riboflavin soak is done after the excimer laser treatment is completed. With IntraLASIK, the flap is replaced and then the UVA exposure is done. Once the UVA exposure is complete, if the epithelium has been removed, a bandage contact lens is applied just like after PRK treatment.
What is IntraLASIK XTRA and PRK XTRA?
IntraLASIK XTRA and PRK XTRA are procedures that combine either IntraLASIK or PRK with a prophylactic treatment using Avedro’s KXL Accelerated Corneal Collagen Cross-Linking with Riboflavin. The cross-linking portion is shorter than for therapeutic treatment. Typically there is a 1.25 minute Riboflavin soak time and then 1 minute of UVA exposure.
What is the recovery like?
The recovery is the same as for PRK or IntraLASIK. If the epithelium is removed, after the procedure a bandage contact lens is applied to the eye. The patient is monitored until the epithelium has healed back and then the bandage contact lens is removed. The patient is typically on antibiotic and anti-inflammatory drops for about 1 week after surgery, depending on the cornea’s healing response. Patients would return for regular visits to monitor corneal changes and refractive error changes.
How well does it work?
Typically only one treatment is required. After IntraLASIK, where you have created a flap of tissue on the cornea and have removed some stromal tissue, the structural strength of the cornea is stronger than you started with. Studies have shown that for about 95% of Keratoconus patients the cross-linking procedure prevents further vision loss.
How long does it last?
Over a decade of results have shown that cross-linking appears to last for a long time and there is evidence that the strengthening effect will be permanent. Corneal Collagen Cross-linking with Riboflavin treatment can be repeated if necessary.
What can it treat?
For therapeutic use, it can treat conditions such as Keratoconus, Forme Fruste Keratoconus (an extremely mild or subclinical form of Keratoconus), Pellucid Marginal Degeneration and post-laser refractive surgery ectasia.
For prophylactic use, virtually any patient can be treated with cross-linking to reduce the chance of future development of the above conditions. Patients with thinner than normal corneas, irregular corneal astigmatism, asymmetry on corneal topography, against-the-rule astigmatism or steeper than normal corneas may especially benefit.
Who qualifies for treatment?
Minimum age of 18; Minimum corneal thickness of 325µm; Those with corneal disease such as Keratoconus, Pellucid Marginal Degeneration or corneal ectasia; Those interested in prophylactic treatment. Contact us for questions on qualifying.