FEMTOSECOND LASER SURGERY

Femtosecond lasers are becoming very useful tools in paediatric patients with cataracts and those who require corneal transplantation, according to two presentations at Femto 2013, an international meeting on anterior segment surgery, in Verona. Burkhard Dick MD, PhD, Ruhr University Eye Hospital, Bochum, Germany, noted that he has developed a technique for performing cataract surgery in the eyes of infants using the Catalys femtosecond laser system (AMO, Santa Ana, CA) for anterior and posterior capsulotomy and lens division (if necessary at all). “The most difficult capsulotomies are those in paediatric eyes, and these are among those that will benefit most from femtosecond laser-assisted cataract surgery,” Dr Dick said.

He noted that using this femtosecond laser platform he can employ an “allcomers” approach for femtosecond laserassisted cataract surgery including many difficult cases, such as hard cataracts, small pupils, intraoperative floppy iris syndrome and eyes with co-morbidities such as corneal guttata and glaucoma. He added that the Catalys system is particularly well suited to performing cataract surgery in paediatric eyes because its fluid-filled interface raises intraocular pressure only slightly, making it possible to re-dock the laser to the eye after lens aspiration and perform a posterior capsulotomy. In addition, its integrated three-dimensional optical coherence tomography provides easy visualisation of the posterior capsule.

His experience to date in 20 infant eyes has yielded a few important pearls, he said. For example, he has found that the elasticity of the anterior and posterior capsule in young eyes appears to cause capsulotomies to widen after they are created. It is therefore necessary to make capsulotomies smaller initially in infant eyes. He and his associates (Tim Schultz MD) are evaluating a correction factor they have devised to compensate for this phenomenon.

Another finding is that the new interface with 12mm inner diameter (LOI12) is designed for small palpebral fissures which makes it easier to perform surgery in small infant eyes. “One drawback currently is that with all of the platforms – based on the manuals – the principal contraindication is a patient below the age of 22, you therefore can perform this kind of surgery only 'off label' with the respective mandatory permissions including the fully informed consent of the parents,” Dr Dick added.

Intrabubble DALK

Femtosecond laser can also enhance the outcomes of deep anterior lamellar keratoplasty (DALK) in paediatric eyes, reducing the risk of perforation and improved visual acuity results, said Luca Buzzonetti MD, Bambino Gesu Children’s Hospital, Rome, Italy. Dr Buzzonetti said he performs DALK procedures in children’s eyes using a 60 KHz Intralase femtosecond laser (AMO). In addition he uses an alternative to the big-bubble technique called the intrabubble technique. In the big-bubble technique, air is injected beneath the stroma remaining after an anterior lamellar trephination in order to remove as much stroma as possible and leave a smooth interface. The intrabubble is different primarily in that it involves the use of a femtosecond laser to create a channel for the air injection part of the procedure.

When performing the procedure he first creates the intrastromal channel by creating a partial side-cut angled at 30 degrees with an arc length of 25 degrees in a position corresponding to a 6.0mm diameter trephination. The intrastromal channel extends to just 50 microns above the endothelium. He then performs a full lamellar cut 100 microns above corneal thinnest point which intersects the intrastromal channel and which he uses for the base of a mushroom trephination.

In addition, because the suction ring of the Intralase laser is too big for the smallest eyes, in those cases he applies the laser cone directly onto the eye surface and uses silk sutures to attach the conjunctiva to the patient's skin in order to immobilise the eye. He noted that the intrabubble DALK procedure appears to greatly reduce the chance of graft rejection compared to penetrating keratoplasty also in paediatric patients. For example, at his own centre the rate of graft rejection among paediatric patients was only 10 per cent at one year’s follow-up in eyes undergoing intrabubble DALK during the years 2010 and 2012 compared to 40 per cent in those who underwent penetrating keratoplasty by mechanical trephination.

In addition, during those same years the mean refractive and visual outcomes were better in eyes that underwent keratoplasty with the femtosecond laser-assisted intrabubble technique than it was in those who underwent big-bubble DALK with a mechanical trephine. That is, the mean spherical equivalent at one postoperative year was -1.3 D in the femtosecond laser group, compared to -4.0 D in the mechanical trephination group. In addition, best corrected visual acuity was 0.8 in the laser group compared to 0.6 in mechanical trephine group and the respective values for refractive astigmatism were -2.8 D and -5.8 D.

“Paediatric keratoplasty is still a challenging surgery, but the femtosecond laser may improve the outcomes because the lamellar geometry increases the contact between the donor and recipient corneal tissues providing ideal suture settings and improving the refractive result,” Dr Buzzonetti concluded.