Technique intra-operative findings and postoperative regimen
Surgeons should not use home-made solutions or riboflavin in their corneal cross linking technique, as it leads to unreliable results, Dr. Paolo Vinciguerra told gathered delegates here on Tuesday.
Dr Vinciguerra outlined his cross linking technique (CXL) . He said he began with 2% pilocarpine drops for protection of the lens and retina.
The light reaching the internal structures of the eye is decreased by the square of the reduction in the pupil diameter, he said. So if a 6mm pupil is 36 units, then a 2mm pupil is just 4.
He said he administered pain medication 30 minutes before the procedure, followed by oxybuprocain hydrochloride 0.2% and lidocaine five minutes before CXL.
He advised that a laser test should be performed with a UVA meter, that power should be 3mW/cm2 Calibration should be extremely precise, plus or minus 0.1mW a cm2 .
Focusing, too, is very important. Out of focus can result in a dangerous or ineffective dosage, he said.
The technique itself consisted of a 9mm diameter central epithelial abrasion with an Amoils brush. A riboflavin 0.1% solution is applied, at 2 drops every minute for 30 minutes.
Do not be tempted to shorten treatment time, he said. Do not use home-made solutions and remember, surface must remain moist to avoid haze formation, he said.
He said at the end of the treatment he used cyclopentolate 0.5% along with hyaluronic acid and antibiotics, until re-epithelisation and a bandage contact lens.
He said intra-operative findings were an important subject of discovery, to understand the real shape of the cornea without the masking effect of the epithelium.
It is important, too, in order to determine the changes occurring after epithelial remove and to document the changes induced by CXL. He said intraoperative findings helped explain why BCVA and topography deteriorate during the following three months.
Why are these late changes occurring? After any epithelial abrasion the physiological rearrangement of the layers takes weeks to complete, he said. Only when they epithelium is back to normal, and its masking function is reestablished, does the flattening effect of CXL begin to appear, at about 3 months.
He said apparent corneal thinning is only temporary because riboflavin solution contains dextrane that together with the exposure of the denuded cornea to the air dehydrates the stroma.
Epithelium takes week to return to normal thickness as the stroma rehydrates. And there is an increase in fibre diameter due to CXL, and corneal thickness can even increase with time, he revealed.
The contact lens can be removed at the end of re-epithlialization, generally 2 to 3 days. The patient should use unpreserved articifical tears for 3 – 6 months and unpreserved steroids for up to 2 weeks. Longer administration reduces the cross-linking effect, he concluded.