Femtosecond laser-assisted cataract surgery: How far have we come?

Reviewed by Dr Bruce Allan, Dr Lucio Buratto, Dr Ahmed Assaf, Dr Alex Day, Dr Thomas Laube, Dr David O’Brart and Dr Anil Pitalia

Eight years after femtosecond laser-assisted cataract surgery (FLACS) was introduced, controversy about its role continues. Cost remains the main obstacle to adoption of the procedure, but enthusiasts among FLACS users appreciate the precision, reproducibility and safety that the femtosecond (FS) laser brings and believe its full potential to provide benefits remains untapped.

To support, improve and expand its use, researchers are conducting studies investigating outcomes, the effects of technique refinements, and implementation strategies that would enable wider adoption.

During the XXXV Congress of the ESCRS, an international panel of expert FLACS users gathered to share their research and insights, and to learn from the experiences of their colleagues.

Dr Julian D. Stevens of Moorfields Eye Hospital, London, United Kingdom, led the meeting in which more than 20 surgeons participated. The attendees came from Egypt and countries across Europe and all have been using different FS laser systems.

Optimising capsulotomy

Although it was reported in some older papers that FS laser capsulotomies were associated with an increased risk for anterior capsular tears, an updated Cochrane review including data from 14 randomised controlled trials (RCTs) found no statistically significant difference between the laser technique and manual capsulotomy, said Dr Alex Day, also from Moorfields Eye Hospital.

Dr Day noted that because eye movement affects the accuracy of laser pulse placement, speed of capsulotomy creation is important. He suggested that the fast capsulotomy cut times of approximately one second or less are preferable, and he noted that not all available systems meet that target.

Dr Burkhard Dick, chairman of the University Eye Hospital in Bochum, Germany, and colleagues evaluated other parameters for optimising capsulotomy in studies using a certain system (Catalys Precision Laser System, Johnson & Johnson Vision). In their RCT, they found that vertical spot spacing mattered.¹ Increasing the vertical spot separation from 10 to 15 μm improved cut quality and reduced both the number of tags and treatment time.

Results of another RCT by the same group evaluating centration methods favoured OCT-based scanned capsule centration over pupil centration for achieving complete capsule overlap of the IOL optic, independently of IOL design, for up to a 5.1-mm capsulotomy.² With a 4.7-mm capsulotomy, complete overlap was achieved regardless of centration method and IOL design.

Dr Day noted that there is a trade-off of decreased rim strength with decreasing capsulotomy size. A poll of the attending experts showed that a large majority created a 5-mm capsulotomy for most patients. Others more routinely targeted a smaller diameter, as small as 4.5 mm, but overall, the plan depended on characteristics of the IOL, capsule and/or cataract.

Looking to the future, which will bring new-generation IOLs with smaller optics and the possibility of hanging the IOL optic on a FS laser-created capsulotomy, Dr Stevens raised the possibility of transitioning to smaller capsulotomies.

Dr Day pointed out that ideally the laser should centre the capsulotomy on the visual axis or undilated pupil centre, and the former would necessitate addition of a fixation target.

Tilt compensation

The participants also addressed their desire for system modifications to address the problems of eye movement or eye tilt from misaligned docking. The general consensus was that the ideal solution would be to have software upgrades that would identify tilt and recalculate the treatment delivery.

Other suggestions included decreasing light intensity to minimise eye movement resulting from Bell’s phenomenon and refinements that give better control for achieving optimal patient head positioning. Dr Lucio Buratto, who works in private practice in Milan, Italy, suggested that the new bed (Catalys System Mobile Patient Bed) for the Catalys laser might be helpful for addressing the latter issue.

The need for detecting tilting of the crystalline lens was also addressed. Dr Stevens suggested that lens tilt and other measurements such as angle kappa that are captured with preoperative diagnostics should be transferrable to the laser and similarly compensated for through software calculations.

Astigmatism correction

Despite enthusiasm for the ability of the laser to create more precise and more consistent astigmatic incisions compared with a manual technique, there are no solid data showing use of the laser leads to better outcomes for reducing astigmatism.

Dr Stevens said he uses the Catalys laser to perform intrastromal astigmatic keratotomy (ISAK), and he explained that he favours this technique over penetrating incisions because it provides better rotational/angular alignment, is associated with better postoperative comfort for patients, and theoretically eliminates infection risk.

In addition, the incisions heal quickly, visual recovery is fast, and, according to his data, stability is achieved by 1 month and maintained in patients having follow-up to 2 years.

“Unlike penetrating incisions, ISAK does not seem to result in cylinder overcorrection unless there is anterior penetration of the arc because of vertical gas breakthrough,” said Dr Stevens.

With that in mind, he noted that anterior surface detection and tilt compensation are critical for ISAK, and Dr Stevens also called for all systems to have automated identification of the steep corneal meridian to guide AK placement in order to minimise angle error.

He noted that achieving the desired result with ISAK requires complete separation of the arc walls. To avoid residual bridging of corneal fibres, Dr Stevens said the treatment should be performed with high power, aiming to generate sufficient gas to assure separation of corneal lamellae.

He also mentioned an outcomes study undertaken at Moorfields Eye Hospital showing that while ISAK was effective in reducing astigmatism, there is room for improving its predictability.³

“We found corneal biomechanics accounts for about half of the scatter in outcomes, and this is a place where we think Brillouin scanning to measure corneal elasticity in individual eyes may be important in the future,” Dr Stevens said.

In a discussion on methods of placing reference marks for aligning the horizontal corneal meridian, Dr Thomas Laube, who works in private practice in Düsseldorf, Germany, described his use of a sterile disposable ink pen (Devon utility marker, Covidien) to mark the conjunctiva when performing ISAK with the Catalys laser. He said the markings are clearly visible in the OCT image and are easily removed with a sponge.

Consistent with the outcomes study mentioned by Dr Stevens, Dr Anil Pitalia, SpaMedica Eye Hospitals, Manchester, UK, presented a comparative analysis of outcomes achieved in 52 eyes that had toric IOL implantation and 36 eyes treated with FS laser ISAK for up to 2 D of astigmatism.

Dr Pitalia noted he prefers to use the laser because it is simpler, but his results showed toric IOL implantation was associated with greater predictability and less residual astigmatism, particularly in eyes with >1.5 D astigmatism preoperatively.

Dr Stevens suggested that some ISAK undercorrections that occurred in his series may be due to tissue bridging that can be easily addressed postoperatively at the slit lamp.

Financial feasibility

The ability of manufacturers to undertake future developments of FS lasers for cataract surgery will depend on increased use to drive profitability. Achieving the necessary level of uptake in the UK will require integrating FLACS into the public health sector, said Dr David O’Brart, St. Thomas’ Hospital, London.

Recognising the current financial obstacles to laser installation at NHS facilities, Dr O’Brart and colleagues conducted a time and motion study of high-volume cataract surgery comparing FLACS and conventional phacoemulsification. The aim was to determine if a “hub-and-spoke” model for FLACS could improve surgical throughput and make it more economically viable.

In the hub-and-spoke model, the FS laser portion of the procedure is performed by a trained ophthalmic nurse or technician in a dedicated room (the hub). Patients are then fed into the operating rooms (ORs, the spokes).

Results of a randomised controlled, real-world study in which the ophthalmologists-in-training were doing the surgery showed that FLACS significantly reduced the average total time spent in the OR by about 3 minutes compared with conventional phacoemulsifcation.

“This is the first evidence that the FS laser pretreatment can reduce the duration of the operation,” Dr O’Brart said. However, this study used a 1:2 hub and spoke model and the average overall cost per case was about ₤150 higher for the FLACS procedure.

A sensitivity analysis was performed to see if modifications of the hub:spoke ratio and cost of the patient interface could reduce the cost of FLACS so that it would be more competitive with conventional surgery. The analysis showed that the parameters at which FLACS could approach this breakeven point might be unrealistic. They involved a 1:4 hub and spoke model, an annual volume per centre of 6,000 surgeries, and discounting the patient interface cost about ₤30.

“In the real world where there is a finite amount of money available, the administrators who control spending would not agree to purchase the lasers unless there is proof that the results of FLACS are much better than conventional surgery,” Dr O’Brart said.

Experience in the Netherlands supports Dr O’Brart’s conclusion. Dr Frank Kerkhoff from Maxima Medical Centre, Eindhoven Area, the Netherlands, told how an effort to obtain approval for purchase of an FS laser at the public hospital where he operates proved fruitless after the National Health Institute decided not to provide full reimbursement for such cases because there was insufficient evidence to show it added value.

“Thus, we have decided to use the laser only for complicated cases where we feel use of the laser increases safety,” Dr Kerkhoff said.

Dr O’Brart suggested that one way to bring the FS laser into broader use would be if the equipment manufacturers developed and funded surgical centres for the procedures.

Dr Pitalia stated that such “mega centres” could succeed in metropolitan areas, but may not be viable in less densely populated regions considering that patients do not want to travel far for their surgery.

Other participants, however, saw the potential for such a change coming in a world where cataract surgery will become even more automated and performed by a dedicated subspecialty group of surgeons.

Improving outcomes in challenging cases

The benefits of using the laser to facilitate surgery in a variety of complex situations was highlighted by Dr Ahmed Assaf, Ain Shams University, Cairo, Egypt. Dr Assaf presented cases of hard cataract, which he said is a common scenario that he sees. In these cases, he uses the laser to segment the nucleus into quadrants and then to soften the lens.

His approach is based on the results of a study he conducted that compared ultrasound energy use in FLACS and conventional phacoemulsification cases using a quick chop technique. With eyes stratified by nuclear density using the LOCS III system, Dr Assaf found that for eyes with NS 3-4 cataracts, overall ultrasound energy use was significantly less when performing FLACS.

He found no difference in overall ultrasound energy use between the two surgical groups in eyes with NS 5-6 cataracts. Analysing data for the NS 5-6 cataracts by phase of the procedure, Dr Assaf also found no significant difference between FLACS and conventional phaco in ultrasound energy used for nuclear disassembly. However, ultrasound energy use during quadrant removal was significantly lower in the FLACS group.

“This study shows that laser segmentation in eyes with very dense cataracts does not increase efficiency as we thought it would, probably because the laser does not treat the most posterior area of these lenses. However, there is a benefit for softening these cataracts with the laser to increase efficiency during quadrant removal,” Dr Assaf said.

Other challenging cases where Dr Assaf said he finds the laser especially helpful include eyes with weak zonules and subluxated lenses. He said he also uses the laser in eyes with white cataracts, but for capsulotomy only.

In these cases, Dr Assaf reduces the incision depth from 600 to 400 μm, sets horizontal spot spacing to 10 microns, and increases his vertical spot spacing to 16 μm.

“Using the laser for capsulotomy only can convert a white cataract case from challenging to routine,” he said.

Dr Assaf added that sometimes he will find a tongue at the capsulotomy edge when using the laser for capsulotomy in eyes with white cataract, but he has not found it to be of any clinical significance, as it has not affected the course of the surgery.

Dr Assaf said he also finds the laser helpful for performing the capsulotomy when there is an anterior fibrous plaque on the capsule. In this situation, he increases the incision depth to 800 μm to assure the cut penetrates the plaque.

“Some manual cutting may still be needed, but the laser treatment greatly enables completion of the capsulotomy,” he explained. He also appreciates having the laser to make the capsulotomy in eyes with phacomorphic glaucoma where a shallow anterior chamber makes manual capsulorhexis challenging.

Remaining vigilant

The meeting concluded with a video presented by Dr Buratto showing a case where the laser’s OCT imaging erroneously read the anterior cornea and capsule surfaces, resulting in the treatments being delivered too posteriorly. After recognising that the capsulotomy was made inside the nucleus, Dr Buratto suspended the laser procedure and, therefore, avoided misplacement of the laser lens treatment into the vitreous cavity.

The experience served as a reminder that while the laser avoids certain sources of human error and automates multiple steps of cataract surgery, users must still pay careful attention to what the laser will be doing.    

“The precision benefits of the laser make surgeons very trusting of its performance. However, surgeons must be mindful to not flash quickly through all of the screens, assuming that the OCT pick-up of the lens capsule position is always correct,” said Dr Bruce Allan, Moorfields Eye Hospital.

“There is still a need to carefully review all of the information before pressing the button to proceed. Laser manufacturers can help surgeons at this stage by flashing up warnings where lens dimensions are measured outside two standard deviations from population mean figures.”

References

1.     Schultz T, et al. J Cataract Refract Surg. 2017;43:353-357

2.     Schultz T, et al. J Refract Surg. 2017;33:74-78.

3.     Day AC, et al. J Cataract Refract Surg. 2016;42:102-109

Dr Bruce Allan, MD

E: bruce.allan@ucl.ac.uk

Dr Lucio Buratto, MD

E: iol.lasik@buratto.com

Dr Ahmed Assaf, MD

E: assaf.ahmed@gmail.com

Dr Alex Day, MD

E: alex@day.ac

Dr Frank Kerhoff, MD 

E: ft.kerkhoff@gmail.com

Dr Thomas Laube, MD

E: thomas@drlaube.com

Dr David O’Brart, MD

E: davidobrart@aol.com

Dr Anil Pitalia, MD

E: anil.pitalia@spamedica.co.uk

Dr Julian Stevens, MD

E: jds@uk.com

The meeting of expert users was organised by targomed GmbH and supported by an educational grant from Johnson & Johnson Vision. Drs Allan, Assaf, Buratto, Day and Laube have no relevant financial interests to disclose. Dr O’Brart has received consultancy fees from Alcon Laboratories and support for his research work through a non-commercial grant. Dr Stevens is a consultant to Johnson & Johnson Vision.