Cataract is responsible for half of the global burden from vision impairment [1,2]. In the western world, phacoemulsification is the surgical procedure of choice routinely providing excellent visual and safety outcomes [3–7]. Nevertheless, it is not a perfect procedure and room for improvement exists. Complications such as endophthalmitis, cystoid macular oedema, endothelial cell damage, vitreous loss and retinal detachment remain sight threatening concerns [8–12]. The femtosecond laser is now commercially available to perform three key steps in small incision cataract surgery: capsulotomy, lens fragmentation and wound construction [13–15]. This review outlines the clinical reasons for converting to laser cataract surgery (LCS), how to flatten the learning curve and the various logistical issues involved when introducing the procedure to the practice.
HOW DOES THE FEMTOSECOND LASER WORK IN CATARACT SURGERY?
Femtosecond lasers work on the principle of photodisruption brought about by a tightly focused beam of ultrashort pulsed light energy with enough peak power to create plasma. The focused femtosecond pulses induce optical breakdown with significantly less pulse energy, thereby minimizing collateral damage [16,17].
The laser beam characteristics differ for corneal and lens application with respect to the ‘numerical aperture’, that is the ratio of the focal length to the diameter of the focusing lens. As compared with corneal refractive procedures, lens manipulations require lasers to focus on a larger target volume and have a deeper penetration. This is accomplished by using a lower ‘numerical aperture’, which results in a larger focal spot size. Due to the increase in spot size and strong scattering losses inside the sclerotic crystalline lens, the pulse energy needs to be increased by a factor of 5–10 to cause photodisruption of the lenticular tissue. In addition, due to variable anatomy of the anterior segment, it is essential to have an imaging system capable of guiding the laser in order to maintain an adequate margin of safety relative to the posterior capsule.
At present, four femtosecond laser systems are commercially available for cataract surgery: LenSx (Alcon LenSx, Ft Worth, Texas, USA), OptiMedica (OptimedicaCatalys, Santa Clara, California, USA), Victus (Technolas GMBH Munich, Germany) and LensAR (LensAR Inc. Orlando, Florida, USA). Variations in docking and imaging form the most significant differences between these systems. LenSx was the first commercially available system for LCS. It uses a disposable curved patient interface for docking and live optical coherence tomography (OCT) imaging. This has been approved by the United States Food and Drug Administration (FDA) for constructing corneal incisions, anterior capsulotomy as well as lens fragmentation.
Optimedica utilizes a fluid-filled interface and spectral domain OCT imaging. LensAR also uses a fluid-filled interface, but the imaging is based on Scheimpflug principle. It has two separately packaged parts to deliver laser energy: a commercially available suction ring with spring loaded syringe to fixate the eye and an index matching eye docking to match refractive index of the cornea and optimize beam targeting accuracy. Currently, both devices have obtained FDA approval for anterior capsulotomy and lens fragmentation. Victus, with a curved pressure sensing interface, has CE (Conformite Europeenne) Mark approval for corneal incisions, anterior capsulotomy, lens fragmentation and refractive procedures.
THE PROCEDURE (ALCON LenSx)
The initial steps during LCS involve programming the lens, capsulotomy, primary corneal incision, secondary corneal incision and astigmatic keratotomy, if needed. A disposable patient interface is then docked to the patient's eye under topical anaesthesia. Sensors in the delivery system detect the objective's position and applanation force, which is indicated on the screen. After correcting the centration to the limbal landmarks, anterior capsular offset, lens offset, corneal thickness and wound tunnel lengths are selected on a live microscopic OCT image. This is followed by delivery of the laser energy, which can be stopped at any point by releasing the footswitch. The procedure is performed in a sequence of capsulotomy; lens fragmentation; primary and secondary corneal incisions; and arcuate keratotomy.
After the completion of the laser procedure, the patient is shifted to the operating room. The laser-created corneal incisions are opened under strict surgical asepsis. Further steps follow as per conventional phacoemulsification with careful removal of the capsulotomy button and lens fragmentation under viscoelastic cover.
IS THERE ANY EVIDENCE THAT IT IS ‘SUPERIOR’ TO STANDARD SURGERY?
Current research suggests that the use of femtosecond lasers in cataract surgery will provide selective benefits both for the surgeon and the patient; however, there remains little if any evidence that LCS provides superior safety or visual outcomes as compared with conventional phacoemulsification.
Previously, we have shown that there is a learning curve for LCS, which may initially lead to an increased complication rate. This was moderately exaggerated in surgeons not familiar with the use and limitations of a femtosecond laser [18▪,19,20]. Our follow-up data suggest that the learning curve is relatively short, and once overcome, the safety outcomes are comparable, if not better, than standard phacoemulsification surgery (T.V. Roberts, M. Lawless, S.J. Bali, et al., in preparation). Increased surgeon awareness, improved training techniques and continuing development of company software have contributed to the flattening of the curve.
Although clinically we are yet to demonstrate superior outcomes, the laser has definite advantages to standard surgery in some areas. It produces a demonstrably more precise capsulotomy with respect to size and centration [21,22]. Friedman et al. found that the deviation from intended diameter for the resected capsular button was 29 + 26 μm for the laser technique and 337 + 258 μm for the manual technique. As would be expected, an accurate capsulotomy with the femtosecond laser has been shown to result in better intraocular lens (IOL)–anterior capsule overlap and hence better IOL positioning . Femtosecond laser capsulotomy has also been demonstrated to produce less IOL tilt and decentration as compared with manual continuous curvilinear capsulorhexis (CCC) [23,24]. In this study, the authors noted that manifest refraction values correlated with total IOL decentration during the postoperative period. Other groups have also reported a more accurate effective lens position and tighter refractive outcomes with LCS [25▪].
Extrapolation of these data suggests that LCS may provide superior refractive outcomes by providing a more stable anteroposterior and central IOL position. This may hold special significance for premium IOLs, which are often implanted in patients who demand a ‘near-perfect’ vision [26–28].
Laser lens fragmentation
There are few published studies at this point that report reduced ultrasonic energy utilization after laser lens fragmentation. Palanker et al.  published one of the first series of cases undergoing LCS. It was found that laser lens fragmentation decreased the perceived hardness of the nuclear cataract during phacoemulsification. They also reported a 39% reduction in the cumulative dispersed energy in laser cut lenses as compared with the manual cohort. In another initial study on the use of femtosecond lasers in cataract surgery, Nagy et al. have also reported that using this surgical technique for lens fragmentation reduces the effective ultrasonic energy and time as compared with routine phacoemulsification surgery. Whether these factors result in lower rate of endothelial cell loss has not been proven. Takács et al. compared central corneal thickness and endothelial cell counts in eyes undergoing LCS and conventional phacoemulsification. Their results showed that femtosecond laser-assisted cataract surgery caused less corneal swelling in the early postoperative period and this may be related to less trauma caused to corneal endothelial cells. However, no differences were evident between the groups at later postoperative follow-up examinations.
Femtosecond lasers can provide complex and precise corneal incisions. Manual creation of incisions makes it difficult to control the length and architecture of the incision tract. Masket et al. have shown, although in cadaver eyes, that manually created incisions are more deformable under pressure and hence may potentially result in more leakage after cataract surgery. Femtosecond-created incisions are more reproducible and stable. But there is no in-vivo evidence that this translates into lower leak rates or lower rates of endophthalmitis. Femtosecond lasers also have the ability to produce very accurate corneal relaxing incisions [33,34]. The advantage of having these lasers to perform quality intraoperative relaxing incisions to reduce preexisting astigmatism or counteract induced cylinder is a potentially significant benefit. Literature suggests that between 9 and 30% of IOLs will rotate by 5 or more degrees by 12 months [35,36]. As IOL rotation effectively reduces the power of the toric correction, the use of laser-created incisions may provide a more stable and accurate result over the use of toric IOLs for some astigmatic patients.
Visual and refractive outcomes
Mihaltz et al. published results of a prospective study comparing 48 eyes that underwent femtosecond capsulotomy and 51 eyes that underwent CCC. The authors noted fewer internal aberrations with femtosecond capsulotomy but no significant difference in uncorrected and corrected distance visual acuities between the groups. In a recent prospective randomized trial consisting of 20 eyes with laser capsulotomy and 25 eyes undergoing CCC, Kránitz et al. noted that femtosecond laser capsulotomies resulted in better corrected distance visual acuity than their manual phacoemulsification cohort.
We analysed the visual and refractive results of the initial 129 eyes that underwent LCS and receiving an aspheric monofocal implant (Acrysof SN60WF, Alcon Laboratories Inc., Texas, USA), and compared the results with a retrospective consecutive cohort that had undergone manual phacoemulsification surgery . The absolute mean difference from the intended spherical equivalent refraction was 0.29 ± 0.25D for the LCS group and 0.31 ± 0.24D for the manual group (P = 0.512). Although this difference was not statistically significant, the results remain promising. The LCS group featured an emerging technique without personalized surgeon factors compared with a highly refined manual cohort. In another series of eyes undergoing LCS and multifocal IOL implantation, our group noted that mean spherical equivalent and visual acuity was again comparable with the manual phacoemulsification cohort. The LCS group was associated with an improved level of unaided visual acuity (unpublished).
An interesting analogy for LCS is with the introduction and adaptation of phacoemulsification itself. It was not until 2001 that prospective randomized controlled trials demonstrated beyond doubt the superiority of phacoemulsification over standard extracapsular cataract surgery [39–41]; yet, by then it had been adopted by the majority of surgeons in Western countries and their decision to transition was vindicated. It is not an overstatement to suggest that at this time, the surgeons who have moved to LCS have done so with a belief that although it is currently as good as standard surgery, it will eventually provide superior visual and safety outcomes. Time, or perhaps the introduction of similar randomized controlled trials, may again provide the definitive comparison.
FLATTENING THE SURGICAL LEARNING CURVE
At the time of this review, the author (G.S.) has performed over 250 femtosecond laser procedures. No patient to date has required further treatment due to complications or suffered visual loss. This does not suggest that the introduction of the surgery has not required changes. In our opinion, a few simple precautions and adjustments to surgical technique, and an awareness of the limitations of the femtosecond laser can hasten proficiency and make the transition to LCS relatively painless.
As with any surgery, appropriate patient selection is vital to ensure the success of the procedure. Excluding patients with the following criteria will serve to reduce the likelihood of encountering additional difficulties:
- Pupil that will not dilate to 5 mm;
- Corneal opacity precluding the effective translation of laser energy;
- Advanced glaucoma because of the increase in IOP with applanation and suction;
- Uncooperative or overly anxious patients; and
- Small interpalpebral fissures, especially if one is unfamiliar with the docking of a femtosecond laser.
Femtosecond laser procedure
Docking is paramount to achieving a successful ablation. It is vital to communicate with the patient both the procedure and the impact of their eye position on the surgery. This should be reinforced during the surgery.
As the patient interface is brought down towards the eye, a careful watch for the lid clearance will ensure ease of application to the eye. Access to the eye may be increased by the use of a speculum.
Prior to application, reaffirm the eye position to reduce or avoid eye tilt. Aim to dock centrally to enhance both the position and the interface suction.
The posterior lens fracture should be set at nuclear shadow. It should be ensured that wounds are created at the limbus. In case this is not possible or the wounds seem to be created too centrally, it may be advisable to abort the laser delivery before wounds are created. The incisions may be created manually with keratomes in these cases.
In the operating room
Considering the following steps at surgery will reduce the likelihood of intraoperative complications.
- Ensure that wounds are opened. This may be accomplished with a spatula (Slade spatula) or Utrata forceps.
- Take utmost care to check that the capsule is completely free. There may be micro-adhesions or rarely an area of ‘uncut’ capsule. Failure to notice this could result in anterior capsular tears, which could radiate to the equator and beyond and result in a dropped nucleus.
- Decompress the anterior chamber prior to hydrodissection to avoid a capsular block syndrome.
- Perform a careful hydrodissection. Consider nuclear split prior to hydrodissection if there appears to be excess intracapsular gas.
- Fragment removal technique should depend on laser programme. We would recommend that surgeons transitioning to this technique should use a four-quadrant pattern with a central circular cut. This allows easy removal of the central core and reproducible nuclear fragmentation.
- It is important to be aware that the cortex may be more difficult to remove because of possible heat adherence to the anterior capsule and the fact that there are fewer tags to remove. We recommend a tangential sweep with the automated irrigation–aspiration probe under the anterior capsule.
The decision to add a femtosecond laser to your existing practice demands a number of important considerations.
The laser is an expensive acquisition. Apart from the initial purchase of the laser unit though, the size of the laser requires additional space necessitating renovations to the existing operating room or the use of alternative space within the practice. The equipment will also bring the added costs of repairs, maintenance, insurance and upgrades. Logistically, it is reasonable to assume, at least in the early stages, that the overall surgery time will increase. This will lead either to additional costs for existing staff or a reduction in income due to fewer cases on the surgery list. It is vital therefore that surgeons and administrators have in place a plausible business plan to estimate initial costs, volumes and fees against future projections. On the basis of local estimates, a practice would be required to operate approximately 600 cases in a year to not operate at a loss. This is not practical for all surgeries.
Surgeries will require different approaches if the laser unit is within or outside the operating theatre and this will determine the patient flow. In our practice, the femtosecond laser was placed outside the operating theatre in a specially designed room. Following the laser ablation, the patients are moved a few metres into the surgery preparation rooms. The initial few cases in our practice saw an increase in the average time for each case; however, this has reduced with experience owing to better patient management and efficient utilization of resources.
Currently, the practices with femtosecond technology are likely to be large multisurgeon practices, with or without refractive specialties. As the technology becomes more available and cost efficient, other smaller practices will be in a position to take on the technology. Although most practices already do surgery well, patient perception of the laser and possible increase in fees will raise the expectations of the patients.
Femtosecond cataract surgery is a viable alternative to standard phacoemulsification. It is as safe and effective and has some putative advantages, but clinical superiority is yet to be proven. Awareness of the idiosyncrasies of the femtosecond laser and subtle adjustments to surgical techniques will ensure a relatively flat learning curve and a safe transition for surgeon and patient. Practices will also need to take into account both financial and operational considerations to effectively introduce this technology to patients.
Conflicts of interest
No author has received any grants nor has any conflicts of interests relating to the content of the study.
REFERENCES AND RECOMMENDED READING
Papers of particular interest, published within the annual period of review, have been highlighted as:
- ▪ of special interest
- ▪▪ of outstanding interest
Additional references related to this topic can also be found in the Current World Literature section in this issue (p. 79).
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