Nagy and McAlinden Eye and Vision (2015) 2:11 DOI 10.1186/s40662-015-0021-7 REVIEW Open Access Femtosecond laser cataract surgery Zoltan Z. Nagy1* and Colm McAlinden2,3 Abstract Femtosecond laser (FSL) cataract surgery is in its infancy but is rapidly gaining popularity due to the improved consistency and predictability for corneal incisions and anterior capsulorhexis. It enables subsequently less phacoemulsification energy and time to be employed, which has gains in terms of reduced corneal oedema. In addition, the FSL allows better circularity of the anterior capsulotomy, capsule overlap, intraocular lens (IOL) placement and centration of the IOL. These advantages have resulted in improved visual and refractive outcomes in the short term. Complication rates are low which reduce with surgeon experience. This review article focuses on the Alcon LenSx system. Keywords: Femtosecond, Cataract surgery, Femtosecond laser, Capsulorhexis, Phacoemulsification, Corneal incisions, Corneal oedema, Macular oedema Introduction However, the Nd:YAG laser causes collateral damage Ophthalmology has always been at the forefront in the use and is the reason why it is not used in corneal proce- of lasers (Light Amplification by Stimulated Emission of dures. However, by shortening the wavelength further to − Radiation) and a variety of lasers have been employed for the femtosecond range (10 15), there is a reduction in more than 50 years [1–3]. In 1949, German ophthalmolo- acoustic shock waves that in turn results in markedly gist Dr. Gerhard Meyer-Schwickerath suggested photo- less collateral damage. This also results in a more precise coagulation of the retina with lasers [4]. A laser is a device tissue effect [9, 10]. that emits electromagnetic light via stimulated emission. The femtosecond laser (FSL) first appeared in corneal Ophthalmic lasers operate at one specific fixed wave- refractive surgery as a microkeratome to create the length, pulse pattern, energy, duration, repetition rate, and corneal flap during laser in situ keratomileusis (LASIK) spot size. This enables photons in phase from the coher- [11]. Thereafter the indication has expanded to all types ent, monochromatic laser beam to arrive at the same time of corneal surgery including lamellar and penetrating and place in the target tissue. Hence, by modifying these keratoplasty, ring-segment implantation in keratoconus parameters they may be absorbed in various tissues at and presbyopia inlay pocket creation [12, 13]. The first various depths with varying biological effects. This has corneal FSLs operated with 30 kilohertz, (kHz)). The resulted in lasers being able to target any issue within the repetition rate was then doubled to 60 kHz and the lat- eye. Many lasers operate by molecular vibration, which est 160 kHz FSLs are able to create a corneal flap within causes localized thermal effects such as photocoagulation 10 s. With higher repetition rates, less energy is required (e.g. argon laser) [5] resulting in protein denaturation. to obtain the same tissue effect. FSLs used in cataract Other lasers operate by photoablation such as the excimer surgery employ a pulse duration of 400–800 femtoseconds − laser used in refractive surgery [6, 7] and by photodisrup- (fs) and the energy range is in microjoules (μJ, 10 6 J). tion such as the neodymium: yttrium-aluminium-garent During the surgery of the crystalline lens of the eye, the (Nd:YAG) laser [8] (Fig. 1). FSL energy may be increased to 10–15 μJ (Fig. 2). The Nd:YAG laser has a pulse duration in the nano- The photodisruptive effect is achieved when the FSL − second range (10 9) and causes photodisruption at its beam is sharply focused and generates plasma within the focal point, such as the posterior capsule of the lens. affected tissue. This plasma rapidly expands as an acous- tic shock wave, displacing the surrounding tissue. With time, the plasma cools and cavitation bubbles are * Correspondence: [email protected] formed. At tissue level, photodisruption occurs at the la- 1Department of Ophthalmology, Semmelweis University, Maria u. 39, H-1085 Budapest, Hungary ser’s focal point without any thermal effect or collateral Full list of author information is available at the end of the article © 2015 Nagy and McAlinden. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http:// creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Nagy and McAlinden Eye and Vision (2015) 2:11 Page 2 of 8 Argon Diode Nd:Glass Er:Yag CO2 457-514 nm 805-820 nm 1053 nm 2940 nm 10,600 nm 193 nm 100 nm 400 nm 700 nm 100,000 nm EXCIMER FS Lasers Ultraviolet Visible Infrared Fig. 1 Lasers in ophthalmology; excimer lasers operate in the ultraviolet range whereas femtosecond lasers operate in the infrared range of the electromagnetic spectrum tissue damage [14]. With this photodisruptive effect, the The accuracy of corneal laser refractive surgery is sig- FSL is capable of creating tissue separation and very pre- nificantly higher than in cataract surgery [19], therefore cise cuts within the cornea, lens capsule and crystalline much work is needed to improve refractive outcomes. lens. Patient expectation has risen and doctors need to be One of the most important characteristics of the FSL proficient at communicating with patients to manage ex- during corneal and lens use is the numerical aperture. pectations accordingly [20]. FSLs offer new potential for The numerical aperture significantly affects both the patients and surgeons alike. spot size and volume. With a larger numerical aperture, less dispersion of the laser beam ensues that in turn pro- Review vides a better focused laser beam. Further, the precision Technical aspects of FSLs of the cut depth improves and lower energy is needed to The Alcon LenSx FSL operates with a solid state laser provide the same tissue effect. Therefore, corneal treat- source that produces thousands of fs pulses per second ments require a larger numerical aperture (with a lower (Fig. 3). The laser pulses are delivered via a sophisticated energy level), and vice versa with the crystalline lens. It beam delivery system. This system includes an arti- is important that a FSL treating both the cornea and the culated arm, a series of optical lenses, scanners and crystalline lens simultaneously should have adequate monitors. The Alcon LenSx laser system is capable of flexibility in the energy, pattern and duration of the providing a variable numerical aperture for optimal pulse as well as the repetition rate [15]. performance in both the corneal and lens plane [15]. Cataract surgery is the most commonly performed The first part of FSL assisted cataract surgery with the ophthalmic procedure worldwide [16, 17]. Cataract sur- Alcon LenSx is the docking procedure. The surgeon uses gery has shifted its focus from a purely vision restoration a curved contact lens, which is integrated with a sterile procedure to a refractive procedure. Ophthalmic sur- limbal suction ring (SoftFit PI). The tubing uses a vac- geons not only restore clarity of the optical media, but uum system to fixate the eye. The patient interface is also change the refractive power of the eye. Further, simple to dock and it provides a large viewing and surgi- presbyopic treatment is now possible with the use of cal diameter range that allows the surgeon to perform multifocal intraocular lenses (IOLs) [18]. the peripheral corneal incisions and arcuate keratotomy incisions. The patient interface is associated with eleva- tions in intraocular pressure (IOP) of between 16 and 20 mmHg, which supports conservation of vision and Excimer laser Femtosecond laser ocular perfusion during the FSL pretreatment [21]. The Alcon LenSx system has a built-in high definition optical coherence tomography (OCT) system and a live video to assist with the docking and surgical pattern localization (Fig. 4). The OCT uses the same optical path as the laser beam and is fully integrated and calibrated. Precise superficial Precise deeper effect The OCT covers the complete anterior segment of the effect eye up to the posterior capsule of the crystalline lens. It Fig. 2 Corneal surgery based on photodisruption. Excimer lasers is also capable of assessing the lens density. The LenSx produce precise superficial effects whereas femtosecond lasers produce automatically performs the surgical pattern after pre- precise deeper effects within the cornea and the crystalline lens operative planning by the surgeon and the selection of Nagy and McAlinden Eye and Vision (2015) 2:11 Page 3 of 8 Monitor for the anterior segment Patient interface Fig. 3 The LenSx femtosecond laser settings. The surgeon is able to alter the various treat- Semmelweis University in Budapest, Hungary [22]. Since ment parameters, such as the corneal incision positions, then the United States Food and Drug Administration centration of the anterior capsulotomy, and cut depth (FDA) has granted approval and the European Confor- within the crystalline lens. mité Européene (CE) mark has been granted for FSLs, With the new software version and coupling by the and FSLs are available for the public. There are currently Verion pre-operative assessment system, conjunctival, four international companies producing and providing scleral vessels and iris characteristics are identified and this new technology for cataract surgery. Peer-reviewed recognised. This provides automated recognition and publications are increasing on the subject and it is pre- centration of the procedure. dicted that within a decade, the method will be available The first human FSL assisted cataract surgery was per- in most of the large ophthalmic centres around the formed with the Alcon LenSx in 2008 by Zoltan Nagy at world [23]. Capsulotomy Lens fragmentation Anterior capsule cut Lens fragmentation area Positioning the corneal incisions Fig.