Femtosecond cataract surgery: A review of current literature and the experience from an initial installation

Abstract

Cataract surgery remains the most widely performed intraocular procedure throughout the world. Safety and accuracy of the procedure are paramount and techniques should remain under constant review. Recently, the introduction of the femtosecond laser to assist cataract surgery has provided ophthalmologists with an exciting tool that may further improve outcomes. We review the existing literature and discuss the installation and initial experience of a femtosecond laser into our practice.

Introduction

Cataract surgery remains the most widely performed intraocular procedure throughout the world with an estimated 19.5 million cataract procedures performed in the calendar year of 2011. As the safety and accuracy of the procedure are paramount to both patient and surgeon techniques must remain under constant review.^1,2 The technique of cataract surgery has evolved from large incision extracapsular extraction with basic, single focal intraocular lenses (IOLs) to micro-incision surgeries with improved lens technology. Greater accessibility to surgery and an improved safety and accuracy profiles in general has served to reduce the age at which most patients are undergoing the procedure. With many patients still active in their work and leisure environments this has meant that corresponding patient expectations have also changed with an increasing emphasis on precise refractive as well as visual and safety outcomes. The recent introduction of femtosecond lasers to cataract surgery represents a potentially significant advance in cataract technology.³ Evidence is slowly being disseminated but there remains little published information on the procedure in terms of safety and visual outcomes. This paper attempts to review the current available literature and presents our recent experience with the installation of a femtosecond laser at a multi-surgeon ambulatory centre.

Femtosecond lasers have been used successfully in ophthalmic surgery for a number of years.^4–8 The technology has been applied widely, most notably though in refractive laser surgery in the creation of corneal lamellar flaps.^9,10 Femtosecond lasers have been noted to be more precise than highly sophisticated mechanical devices, with fewer likely collateral tissue effects.¹¹ He et al. suggest that similar to refractive surgery, femtosecond laser technology can deliver these gains to cataract surgery with improvements in reproducibility, centration and safety.³ The preliminary reports on the intraocular use of femtosecond laser are promising.^12,13 Lasers may currently assist or replace several aspects of cataract surgery including; the creation of clear corneal incisions (CCI), creation of the capsulotomy, fragmentation of the lens nucleus and correction of astigmatism through corresponding arcuate incisions. These steps will be discussed below.

Clear corneal incisions

Clear corneal incisions remain the preferred method for surgeons accessing the anterior chamber during cataract surgery. Approximately 72% of US surgeons use CCIs with this figure reaching almost 92% in a corresponding European survey.^14,15 The benefits of using CCIs are speed of recovery and a contribution to improved visual outcomes.³ To offset these improvements, an increase in the incidence of endophthalmitis, particularly since 2000, has been linked to the use of CCIs.¹⁶ Although this review suggested a pooled rate of 0.128% this remains significant and would approximately lead to 24,960 new cases each year. Endophthalmitis is the most feared complication of cataract surgery and its impact should not be underestimated regardless of relatively low incidence. Endophthalmitis after cataract surgery negatively impacts on self perceived vision related quality of life, resulting in poorer psychological wellbeing and a decreased ability to maintain a role in daily life compared to uncomplicated controls.¹⁷ As well as the emotional and clinical costs, the additional financial cost of treating endophthalmitis, including hospital stay, has been calculated at €3688 (approx. $4900USD) in a European study.¹⁸ These are just the minimal increased costs to society as they do not include loss of productivity for patients and carers.

Manually created incisions make it difficult to control the length or architecture of the incision tract which may affect the stability of the wound under pressure following surgery, and potentially allow leakage.¹⁹ Possible detachment of Descemet’s membrane and thickening of the incision site may also contribute. Masket et al. demonstrate, albeit in cadaver eyes, that femtosecond lasers are able to construct reproducible and stable incisions.¹⁹ This is attributable to the controlled and more reproducible generation of squarer incisions and the multiplanar configuration of the corneal wound created. Unpublished data suggests support for Masket et al.’s findings however future, controlled studies are still required.

Capsulotomy

If laser based surgery can produce a reproducibly round, centred and intact anterior capsule, this alone would improve the safety of cataract surgery in a way that could possibly justify the introduction of the technology.

The incidence of anterior capsular tears in the hands of experienced surgeons has been suggested to be 0.79%.^20,21 Of those with an anterior capsular tear, 40% extended to the posterior capsule and 20% required a vitrectomy. Unal et al.²² has shown that when residents perform cataract surgery in teaching institutions, the anterior capsular tear rate is 5.3%, the rate of irregular capsulotomy 9.3% and posterior tear with vitreous loss 6.6%. The reality is somewhere in between the experienced surgeon and training resident rate. The impact on further surgery is measurable and remains significant. In a retrospective audit Ang and Whyte²³ reported that 64.4% of patients with a posterior capsule tear required anterior vitrectomy. This led on an average to an additional 3.9 visits over 11.7 weeks. Of these patients 51% suffered additional complications including a rise in intraocular pressure, persistent uveitis, cystoid macular oedema, retinal detachment and retained soft lens matter requiring removal. Capsular rupture also leads to other problems; Hatch et al.²⁴ have shown that endophthalmitis rates are significantly high in cases with capsular rupture. Patients with capsular rupture were 9.56 times more likely to develop infection than uncomplicated cataract surgery patients although Bhagwandien et al.²⁵ suggest this relationship is higher at just over 16 times more likely if capsular rupture occurs.

Tackman et al. reported that in most cases with laser created capsulotomy, there was a high ease of removal of the capsular button as perceived by the surgeon.²⁶ In fact, almost half of their cases had free floating capsular buttons and required no manual detachment from remaining capsule during removal.

In a small group of porcine eyes, Nagy in 2009¹² showed that the capsule strength was as good, or greater, than a manual capsulorhexus enabling a greater force of stretch before rupture. The smoothness of the capsulotomy edge was also similar to that of a manual capsulotomy. Although Friedman et al.²⁷ also in a porcine sub-group, confirmed a decrease in the strength of laser capsulotomies, as measured relative to the energy used to create the capsulorhexes, the strength remained significantly greater at all measured points compared to the manually created group. One potential flaw identified in the design of these studies is that porcine eyes are significantly different compared to human eyes in terms of the lens capsule elasticity.²⁸ It was recommended that these studies be repeated in human eyes to confirm these proposed benefits. Clinical experience will assist these arguments in time; however, it would already appear that femtosecond assisted surgery may well make a positive difference to the safety of cataract procedures.

Anterior capsulotomy is the primary step in cataract surgery that can influence the position and centration of the IOLs³ (Fig. 1). Consistent, well-centred capsulotomies are likely to reflect in more producible, better refractive outcomes. To that end, Nagy¹² first demonstrated in 2009 that in a porcine eye the LenSx (LenSX Alcon, USA) femtosecond assisted capsulotomy was more precise and rounder than with a manual technique, and the chance of achieving a capsulotomy diameter within 0.25% of intended was 100% in the capsulotomy group compared to only 10% in the manual group. In 2011 he confirmed the laser capsulotomies were more regularly shaped and showed greater centration than the manual cohort. This allowed for better intraocular lens/capsule overlap.²⁹ Palanker et al.¹³ using the Optimedica (Optimedica, USA) system later confirmed the accuracy of the capsulotomy with a mean circularity of 0.942 in 29 lasered eyes compared with 0.774 in 30 manual eyes with a 12-fold improvement in the precision of the capsulotomy. More recently Friedman and associates,²⁷ echo these results in a prospective, randomized study of 39 patients. The deviation from intended diameter of the resected capsule disc was 29 ± 26 μm for the laser technique against 337 ± 258 μm for the manual technique. In the same journal Tackman and associates²⁶ describe the results with the competing LensAR laser system (LensAR, USA). The mean deviation from intended diameter was 0.16 ± 0.17 mm for the laser capsulotomy group as compared to 0.42 ± 0.54 mm for the manual cohort.

Figure 1.

Slit lamp image patient at day 1 with a well-centred IOL and perfect capsulorhexis.

Phacofragmentation

Laser applied to the nucleus will soften the lens and serve to reduce the overall energy and time required within the eye during the remainder of the procedure compared to routine phacoemulsification. Nagy’s original paper with the LenSx laser showed that laser phacofragmentation resulted in a 43% reduction in phacoemulsification power required and a subsequent 51% decrease in phacoemulsification time.¹² This remains the only published data in peer reviewed literature by mid-2011; however, results presented at the American Society of Cataract and Refractive Surgeons symposium in 2010 by Fishkind and associates also confirmed a decrease albeit to a lesser degree.³⁰ The laser units currently available employ varying treatment patterns and this may reflect the initial differences in results. Further experience, both in research and clinical settings will help to optimize these results across the board; however, it will remain to be seen as to whether this represents a clinically significant difference in safety to patients compared to current standard techniques.

Arcuate incisions

Uncorrected refractive error accounted for 66% of eyes at the 10 year follow-up in patients undergoing cataract surgery in the Blue Mountains Eye Study.³¹ In this study 26% of eyes without astigmatism before cataract surgery, developed astigmatism during the immediate term of surgery. The ability of the femtosecond laser to perform intraoperative relaxing incisions to reduce pre-existing astigmatism or counteract induced cylinder is a potentially significant benefit. Consistent, reproducible and accurately placed laser ablations should improve outcomes compared to manually placed incisions. Prospective controlled studies will help to enable this assertion to be confirmed.

Our experience

Our facility is a group private multispeciality practice with its own ambulatory day surgery centre and refractive laser facility located over two levels in suburban Sydney. The surrounding suburbs would be described as middle class.

We have located the femtosecond laser in a purpose built room adjacent to the entrance of the ambulatory day surgery centre. The patient walks with assistance into the laser room and is placed on the operative bed and the procedure performed under topical anaesthesia. The patient is then escorted approximately 3 m to the ambulatory surgery facility where they are then given intravenous sedation and the lens removal and IOL implantation is performed under further topical anaesthesia.

The procedure

All patients undergo a detailed clinical assessment with the ophthalmologist. An in-depth discussion about the risks and benefits of the procedure is followed by an informed written consent for patients to be undertaken for femtosecond cataract surgery. Preoperative evaluation includes slit lamp biomicroscopy, tonometry, measurements of uncorrected and corrected distance visual acuity, manifest refraction and corrected near visual acuity. Specific investigations included measurement of axial length and biometry (IOLMaster V.5, Carl Zeiss Meditech Inc., Germany), corneal topography and lens densitometry (Allegro Oculyzer, Wavelight AG, Germany), specular microscopy (EM-3000, Tomey, USA) and optical coherence tomography or OCT (Stratus OCT, Carl Zeiss Meditech Inc., Germany) for macular thickness. The presence of glaucoma, corneal opacity, hypotony, poorly dilating pupils (<5 mm), lens or zonular instability, blood or any other material in the anterior chamber are currently considered exclusionary for femtosecond cataract surgery.

As per standard cataract surgery protocol patients instilled ketorolac tromethamine (Acular, Allergan Inc., USA) in the operated eye QID for 3 days prior to surgery. The LenSx laser system (Alcon LenSx Lasers Inc., Aliso Viejo, CA, USA) was used to perform all the femtosecond cataract procedures. All surgeries were performed under topical anaesthesia with 0.4% oxybuprocaine. Pupillary dilation was achieved pre-operatively with 1% tropicamide, 10% phenylephrine and 1% cyclopentolate (Minims, Chauvin Pharmaceuticals, England). The initial steps for the procedure involve programing the lens, capsulotomy, primary incision and secondary incision patterns. After all pattern selections and parameter choices are complete, the system is ready to dock to the patient. The LenSx laser system uses a sterile disposable patient interface. The patient interface, composed of an applanation lens, suction ring and tubing, is mounted onto the distal end of the laser focusing objective and serves as a sterile barrier between the patient and the laser. The objective lens is spring loaded to control the applanation force exerted by the objective. The delivery system is lowered until the patient interface makes contact with the patient’s eye. Sensors in the delivery system detect the objective’s position and applanation force which is indicated on the delivery system’s touch screen. The surgeon observes applanation of the cornea using the video microscope, and then applies suction when the cornea is ‘properly’ applanated, i.e., applanation force indicator is in yellow or green zone. The surgical display presents live microscopic and optical coherence tomography images of the anterior segment (Figs. 2 and 3). The control point settings now include limbal centration, marking the corneal incision boundaries, pupil centration, and identification of the depth and position of lens as well as corneal surfaces. Using the OCT image, a selection is made with respect to capsulotomy peak and trough; lens offsets; corneal thickness and wound tunnel length. The laser treatment is then started by pressing the foot switch and the surgical progress is monitored on the video screen. The procedure maybe stopped at any stage by releasing the footswitch. The LenSx performs the procedures in a sequence of capsulotomy, lens fragmentation and corneal incisions, respectively. The capsulotomy is performed in a cylindrical fashion propagating upwards to prevent interference in subsequent laser pulses by the microbubbles generated. The expansion of the lens caused by the generation of gas bubbles may stretch and displace the lens capsule from its original position. In order that the relatively narrow capsulotomy pattern does not miss its target, the lens fragmentation is performed after capsulotomy has been completed. The corneal incisions are the last steps to be completed before the patients are shifted from the laser suite to the operation theatre. Arcuate corneal incisions, if utilized, follow the secondary corneal incisions.

Figure 2.

OCT showing poor docking leading to excessive lens tilt.

Figure 3.

OCT showing excellent docking. Note the absence of lens tilt.

After the completion of the laser procedure, the patients are shifted to the operating room. After careful sterile surgical preparation, the laser created corneal incisions are dissected bluntly with a Slade spatula (Asico, USA). The laser created anterior capsulotomy flap was removed with Utrata’s forceps (Katena Products Inc., USA). The lens segmentation was completed according to surgeon’s preference either with an Akahoshi chopper (Katena Inc., USA) or by using a direct “chop” technique. The surgery is then completed with standard phacoemulsification procedures using the Infiniti Vision System Unit (Alcon Inc., Fort Worth, USA). Following the removal of the lens cortex, the IOL is implanted in the capsular bag.

Post-operative regimen

The standard postoperative regimen included one drop each of 0.3% ciprofloxacin (Ciloxan, Alcon Inc., USA), ketorolac tromethamine (Acular, Allergan Inc., USA) and 0.1% dexamethasone ophthalmic suspension (Maxidex, Alcon Inc., USA) four times a day for two weeks. Steroid drops were then reduced to twice a day for another week. The patients were followed-up at day 1, day 14 and six weeks following surgery.

Results

The first procedure at our practice was performed in early April 2011. At the time of installation the femtosecond laser represented the third LenSx unit in clinical practice throughout the world. As of the end of September, 700 procedures had been undertaken by the eight surgeons operating at our practice. All patients who are technically suitable, that is those who have large enough pupils and an appropriate palpebral fissure and orbit now receive laser LenSx cataract and refractive surgery.

The first 200 eyes, representing the initial experience of surgeons with the femtosecond laser was recorded and has been submitted previously for publication elsewhere.³² The summary of the results confirmed a definite learning curve for all surgeons although there appeared to be a difference between surgeons who had previously used the femtosecond laser for refractive purposes and those surgeons who had not. The experience in the refractive setting suggested a familiarity with intraoperative reactions helped flatten this learning curve. Review of the further completed surgeries would anecdotally suggests that all surgeons are now comfortable with the procedure with evidence of this the continued reduction in intraoperative complications. A corresponding rise in parameters such as free floating capsulotomies would add weight to this data. Of note since the initial installation the unit has already undergone several software upgrades. The revisions served to further automate the procedure for the surgeons. It has been suggested that the femtosecond assisted surgery may have further potential benefits for the corneal endothelium. Although this may be intuitive we do not have enough current data to support this. Further short and long term endothelial cell density data is required.

Practical observations from surgery:

• •There are individual patients who will need to be told that they are unsuitable for surgery even though it would be potentially advantageous. Those with small pupils (small pupil surgery cannot be performed with a laser approach as it is a closed system). For these patients it may be that simply performing the incisions will be appropriate and then the wound opened and the pupil manually increased with OVD or other methods. Those with a narrow palpebral fissure may need to be excluded as well. Our experience is that with smaller hyperopic eyes with steeper corneas it is more difficult to achieve suction. These patients need to decide whether they proceed with conventional surgery or wait until technology catches up with their anatomy.
• •Adequate exposure with a speculum and constant reminders to the patient about fixation help produce well-centred docking and applanation.
• •The femtosecond procedure is rated as relaxed and easy from a patient perspective. From a surgeons perspective it is quite difficult. There is a learning curve with more technical demands and this increases the length of time for the whole procedure both for the initial laser procedure and the time in surgery. Our records have shown that although the length of surgery continues to improve with time the operational flow should be considered carefully prior to undertaking this technology. Beginning the transition incrementally, that is, with capsulotomy and phacofragmentation initially and completing incisions manually may be a useful option. By doing these procedures the learning surgeon remains able to use a block which will not take them out of their comfort zone.
• •The presence of intracapsular gas and laser-induced changes in cortex are unique to femtosecond LRCS and may represent additional risk factors for capsular block syndrome in high-risk patients (Fig. 4). The underlying mechanism appears to be either resisting the flow of injected fluid around the lens, adding to capsular distension, or by increasing resistance around the edge of the laser-cut capsulotomy. Cracking, to allow gas bubble release before hydrodissection may help prevent capsular block syndrome.
• •For surgeons who have now used the technology the relative precision and consistency of the surgery is obvious. Although the corneal incisions generally open with ease it is important to ensure the internal lip is opened and enlarged. This is to ensure the phaco tip is easily inserted and to avoid a strip in Descemet’s membrane.

Figure 4.

Intraoperative image showing the captured gas bubble resulting from the laser ablation.

Conclusion

Evidence already suggests that successful completion of a case in femtosecond assisted cataract surgery does produce a superior wound, more circular and more consistently sized capsulotomy and probably contributes to a reduction in the average phacoemulsification energy and time than in routine manual surgery. The combination of these features should translate to a safer, more accurate outcome for patients.

The technology itself is continually evolving and improving. This will reduce the learning curve and the possibility of intraoperative complications for surgeons undertaking surgery with the assistance of the femtosecond lasers. The use of femtosecond lasers with cataract surgery is an exciting development for both patients and surgeons alike. Further research is required however an ongoing and increasing role is likely.