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Femtosecond Laser-assisted Cataract Surgery

US Ophthalmic Review, 2014;7(2):82-88 DOI: http://doi.org/10.17925/USOR.2014.07.02.82

Abstract:

Despite improvements in surgical technique, certain aspects of manual cataract surgery are performed with limited precision. Femtosecond laser technology enables precise incisions in the cornea and minimizes manipulations and energy required to fragment and emulsify the lens, resulting in less damage to surrounding tissues compared with manual techniques. The technique also results in superior geometric precision and centration, with reported better capsule strength compared with manual capsulotomy. Femtosecond laser-assisted cataract surgery (FLACS) is particularly advantageous in difficult cases, including hypermature and white cataracts. However, it is still not known how technical advantages translate into functional benefits. Over the past 2 years, four unique laser platforms have been introduced. This article summarizes current literature relating to the efficacy and safety of FLACS and compares currently available laser platforms.
Keywords: Cataract, cornea, femtosecond laser-assisted cataract surgery, phacoemulsification
Disclosure: Michael Lawless, MBBS, FRANZCO, is a paid consultant for Alcon. Alcon has reimbursed his travel expenses and paid honoraria/speaker fees to present these scientific papers and clinical findings at various venues. Chandra Bala, PhD, MBBS (Hons), FRANZCO has no financial interest in the products mentioned. Alcon has reimbursed his travel expenses and paid honoraria/speaker fees to present these scientific papers and clinical findings at various venues. Alcon did not fund or sponsor these studies, any of the data, or clinical findings represented in the article.
Acknowledgments: Editorial assistance was provided by Katrina Mountfort, PhD, at Touch Medical Media.
Correspondence: Michael Lawless, MBBS, FRANZCO, Vision Eye Institute, 270 Victoria Avenue, Chatswood, New South Wales, 2067 Australia. E: michael.lawless@visioneyeinstitute.com.au
Support: Alcon sponsored the publication of this promotional piece and is responsible for its content along with Michael Lawless and Chandra Bala. Neither author received compensation from Alcon for their contributions to this article. The content has been independently peer reviewed and verified by the US Ophthalmic Review publication process.

Cataract surgery is one of the most commonly performed surgical procedures worldwide. Between 2000 and 2020, the number of people aged 65 or over is projected to increase from 425 million to 677 million worldwide.1 This is likely to be accompanied by a corresponding increase in the incidence of cataracts and it has been estimated that by 2020, 32 million cataract surgeries will be performed annually (see Figure 1).1

Phacoemulsification, the most commonly performed type of cataract surgery, requires manual creation of an opening in the anterior lens capsule, fragmentation and evacuation of the lens tissue with an ultrasound probe, and implantation of a plastic intraocular lens (IOL) into the remaining capsular bag. Femtosecond laser technology was approved by the US Food and Drug Administration (FDA) in 2010 for use in cataract surgery including the creation of surgical incisions in the cornea, formation of the capsulotomy, and lens fragmentation following initial clinical demonstrations of its efficacy.2 Current femtosecond laser technologies use a near infrared femtosecond laser focused to a spot size of less than 6 μm.3 Femtosecond photodisruption is achieved by generating a plasma in the tissue. This plasma, comprising free electrons and ionized molecules, then expands and causes a shock wave, cavitation, and formation of a bubble, which expands and then collapses, causing tissue separation.3 By fragmenting a cataractous lens, this technique minimizes the potential deleterious manipulations and reduces the energy required to emulsify the lens compared with non-laser-assisted phacoemulsification. Manipulations are performed within a closed chamber offering greater safety, particularly in potential cases of floppy iris syndrome.4,5

Femtosecond laser-assisted cataract surgery (FLACS) potentially offers a paradigm shift in cataract surgery. Clinical evidence in support of the use of the technique is rapidly accumulating, but the technology involves significant financial and logistical factors.6 While concerns persist regarding its cost-effectiveness,7 recent evidence suggests that, despite the initial financial outlay, FLACS represents a viable financialapproach for busy practices.8 However, unanswered questions remain,e.g. whether the anterior capsulotomy made by laser is as smooth as a manual capsulorhexes. Long-term visual and refractive outcomes are not yet known. It is also not yet known whether the technique will result in significantly lower rates of endophthalmitis, dropped nuclei, vitreous loss, and posterior capsular opacification. This article will review the literature relating to the benefits and challenges of FLACS and compare the available laser platforms.

The Benefits of Femtosecond Laser-assisted Cataract Surgery
The benefits of FLACS are described below and summarized in Table 1. However, it should be noted that studies were of varying methodological quality.

Capsulotomy Strength
The femtosecond laser creates a round opening in the anterior capsule by dissecting it with a circular laser pattern crossing the anterior capsule. This has several advantages over manually created openings, which is considered to be the most technically challenging aspect of cataract surgery.9 The capsular openings created in FLACS have increased strength and rupture force compared with those in manual capsulorhexis in cadaveric eyes.2,10–12 This may reduce the incidence of intraoperative tears to the capsular bag, a source of complications in cataract surgery. Initial data on FLACS suggest an incidence of anterior tears of 0.2 %.13 Manual cataract surgery have reported incidences between 0.79 % and 5.3 %.14–17

Capsulotomy Accuracy and Precision
Capsulotomies using FLACS are more precise than manual capsulorhexes.2,11,12,19 The unpredictable diameter observed in manual capsulorhexis may lead to an irregularly shaped capsulotomy and influence the position of the implanted IOL, which may cause a decrease in visual quality.20 Capsulotomies created during FLACS were more regularly shaped than those in manual capsulorhexes, with better centration, and better IOL/capsule overlap compared withmanual capsulorhexes.21,22

Smooth, regular edges may offer superior capsular strength and resistance to capsular tears, although the significance of capsular edge smoothness is not fully understood.23 Two recent studies used SEM to determine capsulorhexis cut quality at different energy settings and evaluated differences between laser and manual technique (see Figure 2).24,25 Both studies found the cut surface was smoother in the manual group.24,25 In FLACS, the degree of irregularity was higher with increased energy settings.25 In a study to evaluate cell death and ultrastructural morphology of capsulotomies, cut edge surfaces were found to be smoother and there was a lower level of cell death when laser pulse energy was reduced to 5 μJ—this level of smoothness was similar to the levels observed in manual capsulorhexis.26 A separate study comparing FLACS platforms and manual techniques noted a marked improvement in capsular edge smoothness with upgrades in all laser platforms (see Figure 2). Unlike previous studies the improvement in smoothness of FLACS capsulotomy edge was confirmed using objective criteria such as coefficient of variation(CoV) and gray level co-occurrence matrix (GLCM) analysis.24 The latter examined the inter-pixel changes in grayness of the scanning electron microscopy (SEM) images of the capsulotomy edge. The study noted that some FLACS platforms approached manual capsulorhexis when usingCoV and were statistically no different when examining GLCM analysis.

FLACS is also associated with less lens tilt,27,28 and fewer internal aberrations,28 which may result in improved optical quality therefore improving postoperative visual acuity and quality of vision.28 Tilting of the lens induces a considerable amount of ocular coma‐like aberrations.29 In fact, poor positioning of an IOL is one of the main indications for removal, exchange, or repositioning of a posterior chamber IOL.30 A study demonstrated a significantly better predictability of IOL power calculation than conventional phacoemulsification surgery.31 However, in this study, the results from the manual group were inferior to those published in other papers, potentially inflating the comparative outcomes.31 As surgical experience increases, it is becoming apparent that different parameters may influence visual outcomes: in a comparison of 6.0 mm versus 5.5 mm capsulotomies, vertical and horizontal tilt were significantly higher in the 6.0 mm group than in the 5.5 mm group.32 Such subtle refinements were not possible before FLACS.

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Keywords: Cataract, cornea, femtosecond laser-assisted cataract surgery, phacoemulsification