The Avedro Ultraviolet Light cross-linking system
Corneal collagen cross linking with Riboflavin (Vitamin B2), or CXL, is a procedure to strengthen a weakened cornea. The commonest cause of a weakened cornea is called Keratoconus - "kerato" means cornea and "conus" meaning conical i.e. a conical cornea.
Jerry Tan Eye Surgery has been offering cross-linking since 2008.
The Avedro KXL systemA newer system, the Avedro KXL system is now available for strengthening the cornea by cross-linking its collagen. The advantages of Avedro include:
Shorter Treatment Time
Firstly, using an ultraviolet light source with higher power allows the treatment time to be significantly shortened. Whereas the older system required an hour for treatment of keratoconus or corneal ectasia, with the Avedro KXL, this has been shortened to 11 minutes - 8 minutes to soak with riboflavin and 3 minutes exposure to the ultraviolet light.
- Better Precision
Secondly, the KXL system provides centre to edge beam uniformity which ensures uniform cross-linking of collagen throughout. An older system provided much greater ultraviolet intensity in the centre than in the periphery, resulting in poorer cross-linking at the sides of the cornea. The uniform beam profile of the KXL system also ensures that small discrepancies in distance of the system to the eye do not affect focusing of the beam as much as with the older system.
Pictures showing the ultraviolet beam profile of the older system (left)
and the Avedro KXL (right).
Notice the high peak of ultraviolet energy in the beam centre of the older system and then a rapid cooling off towards the sides.
|The Avedro KXL system|
Besides cross-linking corneas with keratoconus, the Avedro KXL system has also been used in patients undergoing LASIK. LASIK Xtra™ is an addition to the normal LASIK procedure which seeks to minimise the weakening effects of LASIK on the cornea by strengthening it with cross-linking treatment. Corneas normally become thinner after LASIK because the excimer laser used removes tissue. This effect is more marked when higher degrees of spectacle power are treated. In a small percentage of cases, this thinning causes the cornea to bulge forwards and become distorted in a condition called corneal ectasia.
LASIK Xtra™ is useful in cases where a very thin cornea is expected after the LASIK procedure. This would include cases of high spectacle power and patients with thin corneas before surgery.
The mechanics of LASIK Xtra™
Performing this addition to a normal LASIK procedure only adds an extra 2 minutes 15 seconds of time.
After the excimer laser has been used to reshape the cornea during a LASIK procedure, a small amount of specially prepared vitamin B2 called VibeX™ is applied for one minute to the surface just treated by the laser. The LASIK flap is replaced and the VibeX™ thoroughly washed off the eye. The Avedro KXL system is then positioned over the cornea and ultraviolet light is shone onto the cornea for 1 minute 15 seconds. Even without this extra procedure, a normal LASIK flap needs to be replaced and left on the cornea with the eye open for 3 minutes, to allow it to stick firmly and minimise the chance for flap slippage later.
Our results with LASIK Xtra™
In a series of patients we treated for high degrees of short-sightedness above 800 degrees, benefits were seen among those who had the additional strengthening treatment (LASIK Xtra™). When compared to an earlier group of such patients (before we had the LASIK Xtra™ treatment), LASIK Xtra™ patients had better post-operative vision without glasses, a more predictable outcome, and less return of short-sighted power.
Figure 1 - More patients who had LASIK Xtra experienced 6/6 or better vision, and also 6/12 or better vision after three months.
Figure 2 - After LASIK, the short-sighted power is reduced to almost zero, and is better maintained at that level in the eyes that had LASIK Xtra™. A slight return of shortsightedness is seen among patients who had standard LASIK in the first three months.
Figure 3A & 3B - A slightly bigger scatter of points among standard LASIK patients compared to LASIK Xtra™ patients indicates that the outcome of LASIK Xtra™ was more predictable, and closer to zero spectacle power overall.
Safety of LASIK Xtra™
The Avedro KXL is CE marked and thus approved for use throughout the European Union. It is also approved for use in Canada and Japan. One of the highest volume LASIK centres in Japan, the Shinagawa LASIK centre has now performed over 3000 LASIK Xtra™ cases. Overall, vision was the same as for those who did not undergo LASIK Xtra™ and the cross-linking treatment did not affect the accuracy of the excimer laser in correcting spectacle power.
The Avedro KXL system
- A system to strengthen the weakened cornea by ultraviolet light induced cross-linking with riboflavin.
- Builds on established principles which have been in use with older machines for almost 10 years.
- CE marked for use throughout Europe and also approved for use in Canada and Japan.
- Improvements include much shorter duration of treatment, better precision with more consistent treatment effect and better safety.
- Stabilises conditions like keratoconus and corneal ectasia.
- When combined with laser PRK to smoothen the cornea in early/mild cases of keratoconus, improvement in visual quality is possible.
- Adds a higher level of safety to LASIK in patients with high spectacle powers and pre-existing thin corneas.
LASIK Xtra™ website: lasikxtra.surgery