A decade of FLACS
Precise capsulotomies, complicated cases and premium lenses may be best uses, though costs and limited advantages keep it a niche player for now.
For years after Zoltan Z Nagy MD performed the first femtosecond laser-cut anterior capsulotomy in a human patient in August 2008, femtosecond laser-assisted cataract surgery (FLACS) pulled standing-room- only crowds at ophthalmology meetings around the world.
Yet scepticism ran as high as interest. Forty years of development had transformed manual phacoemulsification cataract extraction into one of the most elegant and successful of all surgical procedures. Visual outcomes and patient satisfaction were excellent, as were safety, efficiency and cost-effectiveness – setting a very high bar for clinically meaningful improvement.
Moreover, while FLACS could reduce the need for phaco, a phaco machine was still required to liquefy and aspirate the nucleus and cortex. FLACS lasers also needed extra floor space and a modified surgical flow, adding to procedure time. So, the question arose, why spend €400,000 for a complicated laser that decreased operating room efficiency, but didn’t deliver patient outcomes measurably better than some forceps or bent needle?
As FLACS enters its 10th year of human use, this question remains pertinent. Despite hundreds of studies, clear evidence of a clinically meaningful advantage for FLACS remains elusive, at least for its routine use in uncomplicated cases of implanting monofocal lenses.
For example, a large case-control study using data from the European Registry of Quality Outcomes for Cataract and Refractive Surgery (EUREQUO) compared visual, refractive and safety outcomes of 2,814 patients undergoing FLACS procedures with 4,987 patients undergoing conventional phaco cataract surgery matched for age, preoperative visual acuity, and similar number of ocular co-morbidities and surgical difficulty variables. It found conventional outcomes were slightly better than FLACS on average. (Manning S et al. J Cataract Refract Surg Dec 2016; 42:1229-1790.)
Similarly, small differences, though mostly favouring FLACS, were found by a meta-analysis of 42 studies comparing outcomes of 9,400 eyes undergoing FLACS with 8,779 undergoing conventional manual phaco conducted by Thomas Kohnen MD, PhD, Professor and Chair of the Department of Ophthalmology at Goethe University, Frankfurt, Germany.
“It appears for routine cataract surgery there is not a very big difference [with FLACS]; it is not a game changer in the way that phaco was,” said Rudy MMA Nuijts MD, PhD, Professor of Ophthalmology at the University Eye Clinic Maastricht, The Netherlands. Large-scale prospective randomised clinical trials are needed to nail down what, if any, advantages FLACS offers for routine cataract care, and these are under way in France and the UK.
However, many surgeons find FLACS valuable for certain niche applications, said Ashvin Agarwal MD, Dr Agarwal’s Eye Hospital, Chennai, India. These range from improving the performance of multifocal and toric IOLs to lens pre-fragmentation reducing risk in complex cases involving zonular dehiscence, intumescent cataracts, very hard nuclei or traumatic injury. A summary of some current productive uses – and limits – of FLACS follows, by surgical stage.
Anterior capsulotomy was the first FLACS capability demonstrated in humans, and may still be the one most commonly used. In the ESCRS-EUREQUO study, the laser was used in 99% of the FLACS cases, followed by nucleus fragmentation in 95%, corneal incisions in 35% and arcuate astigmatic incisions in 5%.
Dr Nuijts uses FLACS primarily for premium IOL cases, both multifocal and toric. “The big advantage is the capsulotomy is more predictable in shape and size, and with premium lenses you want to have the capsule edge completely covering the optic.”
This prevents the capsule from healing asymmetrically, with the anterior and posterior leaves fibrosing together where the capsulotomy runs off the IOL optic, which can tilt or rotate the lens, Dr Nuijts explained. While this doesn’t affect the performance of a monofocal lens much, it can introduce optical aberrations in multifocal lenses and astigmatism with toric lenses. “The incidence is quite low, but you want to prevent that, especially in people who have contributed extra to their own treatment. It takes predictability to the next level.”
In studies conducted by Dr Nagy, of Semmelweis University, Budapest, Hungary, lenses implanted in eyes with FS capsulotomies showed less tilt than those in eyes with manual capsulorhexes, as well as less coma and total higher order aberrations. However, this did not have a big impact on visual outcomes, he said in an interview in the EuroTimes’ Eye Contact video series.
Large studies comparing outcomes with the same lens implanted in manual and FLACS eyes are needed to demonstrate the difference, he noted.
Dr Nuijts said that FS laser capsulotomy is useful for treating capsule phimosis. “You size the capsulotomy and cut out the phimosis, make an incision, put in viscoelastic and remove the rim.”
FS capsulotomies are also an advantage in patients with Marfan’s, subluxated lenses or other capsule instability because there is no movement of the lens that might affect circularity, which can be a problem attempting a manual capsulorhexis, said Boris Malyugin MD, PhD, Professor of Ophthalmology at the S. Fyodorov Eye Microsurgery State Institution, Moscow, Russia. Laser capsulotomy is also useful for white cataracts with less risk of a large capsular tear often seen when attempting a manual capsulorhexis.
Dr Malyugin noted that while precisely sized and centred FS capsulotomies promote even healing for premium lenses, they might also be more prone to anterior capsule tears.
Dr Nagy said that the problem can be decreased by reducing laser power resulting in a smoother capsulotomy edge. Tearing the cap in a circular motion around the edge as with a capsulorhexis, rather than trying to pull it off from the centre may also help avoid tears in cases where the laser cut leaves attached tags, Dr Nagy said.
Laser lens fragmentation helps reduce stress on weakened ocular structures in eyes with Marfan’s and pseudoexfoliation, Dr Malyugin said. Reduced phaco time enabled by pre-fragmentation may also be helpful for eyes with compromised endothelium, such as Fuch’s, which make up about 4% of cataract patients.
Dr Agarwal finds the FS laser especially useful for hard brown cataracts, though not so much for white cataracts, which reflect the laser light. He also uses the FS laser for intumescent cataracts, paediatric cases and patients with shallow anterior chambers.
Studies by H Burkhard Dick MD, Bochum, Germany, and others have shown that laser fragmentation can completely eliminate the need for phaco in softer cataracts, and even speed up the procedure. However, fragmenting softer lenses can actually make cortex removal more difficult, adding as much as five minutes to the procedure overall, noted Dr Agarwal, who recently published a review on FLACS with Soosan Jacob MD (Curr Opin Ophthalmol. 2017;28(1):49-57.)
Dr Nagy noted that the corneal multiplanar incisions were more central at the beginning than was intended. This lead to a redesign of the patient interface, so that it is now possible to place the corneal incisions where the surgeon wants to put them.
Dr Malyugin noted that studies show multiplanar corneal incisions cut by FS lasers are less prone to leakage than manual incisions. However, current FLACS systems may not give enough flexibility in where these incisions are placed, which could result in greater induced astigmatism.
“The lasers place the incisions on a circle, but in most cases the cornea is an oval with horizontal diameter bigger than vertical,” Dr Malyugin said. As a result, if the main incision is closer to the limbus, the paracentesis is a little closer to the centre than is ideal, or vice versa. He looks forward to a new generation of software that will allow correction of this issue, but for now he prefers to use disposable metal blades.
Correcting astigmatism with FS-cut arcuate incisions can be much more precise than manual incisions, in part because the incisions made at surgery do not penetrate, and can be opened up as needed after surgery. Iris registration helps ensure incisions are not displaced due to cyclotorsion, though issues with alignment and even corneal perforation and mis-registration leading to grid profile incisions have been reported, Dr Agarwal noted.
Dr Nuijts has used arcuate incisions, but prefers toric IOLs as an astigmatism solution. “In our hands, toric IOLs are more predictable,” he said.
While FLACS complication rates are similarly low compared with manual cataract surgery, some complications are more common. Pupil contraction, apparently resulting from the release of prostaglandins due to FS laser exposure, is one. A team led by Dr Nagy analysed the reason of pupillary constriction and they found that the reason behind it is partly due to significant increase in the prostagladin level (PG-E) in the aqueous. “This can be completely prevented by dropping non-steroid anti-inflammatory drops (NSAIDS) a day before. Other reasons for pupillary constriction might be the mechanical effect of the bubbles created during the capsulotomy,” said Dr Nagy.
Dr Malyugin said that in an early series of FLACS in his clinic, he was surprised to see a significant proportion of patients having pupil constriction after femtosecond laser application. Dr Malyugin now manages this problem by giving FLACS patients topical NSAIDS for one to two days before surgery.
Iris hooks or a Malyugin ring may also be used, though small pupils generally are a contraindication for surgery, Dr Agarwal said. Bubbles trapped in the capsule also can lead to posterior capsule ruptures if not allowed to dissipate before nucleus removal.
In an ESCRS-EUREQUO study examining all 3,379 FLACS procedures collected for the case-control study, including 562 that were excluded for lack of a control match, FLACS procedures had a total complication rate of 3.3%, compared with 2.3% for conventional surgery. However, only 1.0% of these were “classic” complications, such as posterior capsule ruptures, while 1.9% were directly related to the FLACS procedure, said Mats Lundström MD, PhD, at the XXXIV Congress of the ESCRS in Copenhagen, Denmark. “Some of these complications are not a problem; they are not vision-threatening. They were complications we were looking for with this new technique.” (See Table 1.)
Dr Nuijts noted that FLACS is still in its infancy and is likely to develop further in years to come. He looks forward to the results of large-scale controlled trials that may shed more light on theoretical FLACS advantages, such as better lens stability that might improve visual outcomes.
Dr Malyugin believes routine cataract surgery will one day be completely automated. “Computers are smarter than humans. They play chess, they drive cars, why not teach them how to do surgery?” A skilled surgeon would still be required to run the machine and intervene in case of complications, he noted.
What really holds back FLACS technology, however, is the cost, Dr Agarwal believes. FS systems also need to be easier to use and small enough to fit in existing surgical theatres. “A lot of new machines break through immediately, but the femtosecond laser was not one of them. People still have a lot of questions. If it was quarter of the price a lot of people would say it helps in some cases,” he said.
Sonia Manning: firstname.lastname@example.org
Zoltan Nagy: Zoltan.email@example.com
Boris Malyugin: firstname.lastname@example.org
Rudy Nuijts: email@example.com
Ashvin Agarwal: firstname.lastname@example.org
Mats Lundström: mats.lundstrom@ karlskrona.mail.telia.com