FUTURE OF FEMTO

Over the past few years, femtosecond lasers have made rapid inroads into both cataract and refractive surgery, with procedures that create intrastromal lenticules that can be extracted for myopic corrections, and increasingly automated technology for performing several of the most difficult manoeuvres of the cataract procedure. 
In a discussion held at the XXXII Congress of the ESCRS in London, several leading researchers in refractive surgery reflected on the current state of the art in femtosecond laser technology, the improvements still needed, and the ultimate goal at which to aim.
“When we adopt new technology we have to continue to do good research to make sure that what we’re doing is not going against us,” said Thomas Kohnen MD, PhD, Goethe University, Frankfurt, Germany, who co-chaired the session with John Marshall PhD, UCL Institute of Ophthalmology, London, UK.
Dr Kohnen noted that small incision lenticule extraction (SMILE) is emerging as an important new contender in the field of corneal refractive surgery. The new technique involves the use of a femtosecond laser to first create a lenticule and then perform the side-cut for its removal. 
Dan Reinstein MD, MA (Cantab), FRCSC, DABO, FRCOphth, FEBO, London, UK, noted that in his practice the SMILE technique has been living up to its expectations, providing accuracy and efficacy comparable to that of LASIK but with better spherical aberration control and less biomechanical impact. Moreover, the SMILE procedure now accounts for 80 per cent of his myopic treatments. He pointed out that there have been more than 300,000 procedures performed worldwide, with over 40,000 SMILE procedures performed last year alone in China.
The SMILE technique reduces the tensile strength of the cornea less than is the case with LASIK. This is because no flap is created, and therefore the integrity of the anterior stroma lamellae, which is known to possess greater tensile strength than the posterior stroma, is maintained, Dr Reinstein said. 
It therefore stands to reason that SMILE can be used to correct higher levels of refractive error than is possible with LASIK or PRK. The SMILE technique also has the advantage of cutting through fewer nerve fibres than LASIK, which leads to a lower reduction and faster recovery of corneal sensitivity, and therefore we believe a reduction in dry eye symptoms postoperatively. 
The VisuMax femtosecond laser is currently the only femtosecond laser being used for intrastromal lenticular surgery. In order for accurate 3D intrastromal cutting, a number of technological hurdles have to be overcome; not only does the femtosecond pulse placement 3D accuracy need to be very high and pulse energy very low, but there has to be minimal tissue distortion of the cornea when optically coupling to the femtosecond laser source. This is achieved by using a curved contact glass and by applying suction to the peripheral cornea (not the conjunctiva/sclera) allowing for immobilisation of the cornea using a very low suction force. 
In turn, because the eye is immobilised by the contact glass interface centred on the corneal vertex while the lenticule is being cut, no eye-tracker is necessary, Dr Reinstein pointed out. 
He added that, for any refractive procedure to gain wide acceptance, the safety aspects must be a foremost consideration. There are many people, including some refractive surgeons, who will not undergo corneal refractive surgery because they fear that they might have a complication that would result in an irreversible loss of vision, he pointed out.
“My dream for the field of refractive surgery is that the worst-case scenario possible would be that, after all is said and done, patients’ vision with glasses would always be as good as it was preoperatively. The current situation is that unfortunately we don’t quite yet have that, but we’re working on it based on stromal surface topography guided treatment,” he said.
Dr Marshall noted that SMILE was in some ways a compromise. The original concept was to have a procedure that could be performed completely within the stroma. However, that proved too difficult because of the uncontrollable nature of the cavitation that resulted from the plasma the laser generates in the stroma. 
“Then again, watch this space because there is at least one company, Schwind, that is beginning to use ultraviolet-induced plasmas where the photon concentration is so much less and you get only tiny, tiny plasma formations in the cornea,” Dr Marshall said.

Robo-cat
Paul Rosen FRCS, FRCOphth, Oxford Eye Hospital, Oxford, UK, noted that the advent of femtosecond laser-assisted cataract surgery (FLACS) has elicited concern that surgeons in the future will be largely replaced by robots. However, he maintained that surgeons will always be needed as clinical decision makers. Dr Marshall countered that perhaps the more automated the surgery is, the better.
“I always keep in mind accidents. More than 80 per cent of the air accidents of the last 15 years have been due to human error, so I think we have to bear that in mind. We rarely have system errors in ophthalmology and very often it is our inappropriate decisions that cause the problems,” Dr Marshall added.
Dr Rosen said he largely concurred, but pointed out that humans will be needed to programme the machines and that the effective use of the technology is bound to require certain skills. Femtosecond laser-assisted cataract devices will provide an extension to a surgeon’s skills. 
“These systems will magnify our skills rather than take them away. It’s a bit like the shift from intra-cap to extra-cap and then to phaco. Currently, the vast majority of our residents would be incapable of doing cataract surgery without a phaco machine. In the future they will need a femto machine. I predict that the advantages will be a more reproducible quality in cataract surgery with fewer complications,” he said.

Thomas Kohnen: kohnen@em.uni-frankfurt.de 
John Marshall: eye.marshall@googlemail.com
Dan Reinstein: dzr@londonvisionclinic.com 
Paul Rosen: paul.rosen@ouh.nhs.uk