Chapter 9

Kendall E. Donaldson, MD, MS

THE ORIGIN OF FEMTOSECOND LASER–ASSISTED CATARACT SURGERY

Femtosecond laser–assisted cataract surgery (FLACS) has recently become part of our armamentarium as cataract surgeons. It has given us another option to upgrade our patients with hopes of achieving the most advanced, safest, customized option in cataract surgery. The primary potential goals of FLACS are to achieve better refractive outcomes and safer surgery relative to traditional cataract surgery.

There has been great debate over the proper terminology used to describe this technology. Acronyms include ReLACS (refractive laser–assisted cataract surgery), FALCS (femtosecond-assisted laser cataract surgery), and T-LACS (therapeutic laser–assisted cataract surgery). Finally, the most widely used acronym has become FLACS.

The availability of FLACS and its increasing usage by cataract surgeons has come at a time of a refractive revolution in cataract surgery. Its development has occurred alongside the continued development of presbyopic intraocular lenses. The past decade has seen a dramatic improvement in this technology, allowing us to feel more confident while offering our patients these expanded options for vision correction. Fifty years ago, cataract surgery was performed with one goal in mind: removal of the cloudy lens and replacement with aphakic spectacles. However, by today’s standards, this result would be considered a travesty by both the surgeon and the patient. Our surgery then evolved to include the replacement of the cloudy lens with a spherical distance lens, which was very effective in many patients but left them wearing glasses for astigmatism correction and for near vision. Now, cataract surgery has 2 primary goals: removal of the cloudy lens and replacement with a lens that either gives the best possible distance, near, or both, while correcting astigmatism to give patients high-quality vision at a broader range of distances while providing more freedom from glasses. FLACS has become a tool toward achieving this goal, while giving us a mechanism to achieve better outcomes and improving the safety of the procedure.

Femtosecond lasers were initially used to create corneal flaps in LASIK with the approval of the IntraLase femtosecond laser (Abbott Medical Optics) by the United States Food and Drug Administration in 2000.1 Laser application to the cornea, however, was much simpler, as the cornea was applanated, essentially flattening it so that the laser could be applied in a plane parallel to the surface at a preset distance beneath the applanating interface. The laser had to pass through and cut only one structure, the cornea, and there were no other interfering or surrounding structures that could potentially be damaged by inadvertent laser application. Additionally, with LASIK surgery, patients are generally much younger and healthier, allowing them the flexibility to be positioned as needed and to tolerate the high levels of vacuum required during their laser treatment.

For FLACS, we now need to be able to use these lasers to cut corneal tissue as well as capsular tissue and lens material, while avoiding collateral damage to surrounding structures such as the iris or posterior capsule. Thus, imaging capabilities have been enhanced so that the laser can accurately detect and avoid these surrounding structures to ensure the safety of the procedure.

CURRENTLY AVAILABLE LASER PLATFORMS

There are currently 5 laser platforms available in the United States: 1) LenSx (Alcon), 2) VICTUS (Bausch & Lomb), 3) Catalys (Abbott Medical Optics), 4) LensAR, and 5) the LDV Z8 femtosecond laser (Ziemer), which was CE marked in Europe and recently cleared by the US Food and Drug Administration for use in cataract surgery (corneal incisions, capsulotomy, and lens fragmentation). Each laser is unique on several levels. Four of them can be compared based on the essential features illustrated in Table 9-1 and Figure 9-1.

The Patient Interface

The patient interface is a key differentiating factor among the laser platforms. Both the LenSx and the VICTUS platforms are derived from LASIK-based applanation platforms, whereas the Catalys and LensAR platforms evolved de novo for cataract surgery. In addition, due to the minimal rise in intraocular pressure (10 to 16 mm Hg), the Catalys and the LenSx lasers have been approved for usage in glaucoma patients.^2,3

Since the inception of laser-assisted cataract surgery, Alcon has modified the patient interface from a standard applanating interface to the SoftFit modified applanating interface, with a customized soft contact lens within the applanating cone. This allows the applanating surface to conform to the surface of the eye more accurately. This interface modification significantly decreased the incidence of capsular discontinuities, as it reduced the applanation-induced corneal deformation, or folding, that can occur when pressure is applied to the ocular surface. This modification occurred along with a decrease in the diameter of the patient interface, while also reducing the intraocular pressure elevation necessary to provide adequate vacuum. Corneal folds may introduce artifacts during imaging, ultimately resulting in areas devoid of laser application. These skip lesions result in capsular tags, which, if not identified and managed proactively, can result in anterior capsular tears and, in some cases, posterior capsular extension and potential vitreous loss.

The Catalys femtosecond laser uses a liquid optics interface with 2-piece vacuum docking. Imaging through liquid allows for high-resolution OCT imaging with no interference through other solid interfaces that may induce any deformation of the cornea. A very low intraocular pressure elevation of 10.2 mm Hg occurs during vacuum application.3

The LensAR laser also images through a liquid interface through a patented Robocone 3-piece applanating system. The liquid interface provides high-quality imaging without interference, which is similar to the Catalys laser.

The Zeimer laser also has a liquid optics interface designed to optimize lens fragmentation, while it still has corneal refractive procedure capabilities, including cataract incisions, LASIK flap creation, channels for corneal ring segments, and keratoplasty applications.

All of the lasers require precise 3-dimensional imaging capabilities in order to accurately apply the intended laser treatment. Three of the lasers image the structures through spectral domain OCT. Through a series of OCT images taken in rapid succession, the images are merged to create a 3-dimensional reconstruction of the patient’s eye. The programmed treatment is then illustrated in an overlay using the recreated image (Figure 9-2). The image must accurately determine position of the structures and account for any induced lens tilt in order to avoid inadvertent lasing of surrounding structures. Although safety zones are preset by the surgeon, strict imaging requirements are critical to avoid complications. In contrast to the other laser platforms, the LensAR femtosecond laser uses the Scheimpflug principle to align the camera lens, taking a series of 10 photographs with a rotating camera, which are then fused to create a high-resolution 3-dimensional model of the essential ocular structures. A scanning superluminescent diode with a variable scan rate creates the infrared light that illuminates the eye. It uses a lower scan rate on more highly reflective surfaces to avoid reflection (ie, for the iris) and a higher scan rate for lower reflective surfaces (ie, for the lens and posterior capsule). Through accurate reconstruction of the anterior segment structures, lens tilt is accounted for, and the treatment profile is applied accurately, avoiding surrounding structures.

The anterior capsulotomy is arguably the most important portion of laser application, with the lowest margin of error (requiring the most precision). Some may argue that the lens fragmentation is more critical; however, we generally program a significant safety zone for lens fragmentation, so capsular discontinuities, although rare, are much more common than inadvertent lasing of the posterior capsule. Fortunately, as the lasers have evolved over the past few years, the average laser time necessary to complete a capsulotomy has decreased from 13 to 15 seconds to 1 to 6 seconds for most laser platforms. This allows less time for patient movement, making the incidence of capsular discontinuities much more rare. An incomplete capsulotomy can be a very frustrating problem for the surgeon, taking a simple traditional case and turning it into a challenging FLACS case (Figure 9-3A). This may result from lens tilt, a corneal opacity (such as a scar or fold), an opacity within the anterior chamber (such as a bubble in viscoelastic after placement of a Malyugin ring), misalignment of the laser beam, or a suction break during laser application. Recovery after an incomplete capsulotomy may be challenging in some cases, as it may be difficult to visualize, particularly in those cases involving more complex lens fragmentation patterns that end near the capsulotomy edge. For this reason, many surgeons have advocated the dimple down technique, using a Utrata forceps (or similar tool) to slightly indent the central portion of the capsule, allowing the capsular edge to slightly retract centrally, revealing a 360-degree gutter ensuring a complete treatment pattern before the capsule is removed abruptly.

Since the capsulotomy is created by the coalescence of gas bubbles (through photodisruption, as previously discussed), we know that the capsule edge will not be quite as smooth as it would be in comparison to a manually torn capsulorrhexis. Electron microscopy studies have shown that the capsulotomy edge is irregular (and has been likened to a postage stamp), even with a complete treatment pattern.4 Fortunately, studies have also revealed that the strength of a femtosecond capsulotomy is similar to or stronger than a manual capsulotomy.^4–6 The speed of laser capsulotomy creation makes the laser a particularly useful tool with white cataracts in which the potential increased pressure from capsular distension and the friable nature of the capsule itself makes those cases prone to extension of a capsular tear (known as an Argentinian Flag sign).

The laser has an exceptional ability to create a capsulotomy of a preset size, shape, and centration^7–9 (Figure 9-3B). All of the laser platforms have shown extremely accurate reproducibility and accuracy. The capsulotomy may be centered on the pupil, limbus, scanned capsule, or by some other customized parameter as designated by the surgeon. An accurate centered capsulotomy may not be essential for every monofocal case with current intraocular lens technology; however, this degree of accuracy may be necessary for best results with accommodating lens technology, and particularly with some of the newer lens designs involving dual optics.

Lens Fragmentation

The ability of the laser to prefragment the lens has become a useful tool, particularly in denser cataracts and in eyes vulnerable to ultrasound-induced trauma (ie, Fuchs dystrophy). We currently have a variety of treatment patterns available on all of the laser platforms, allowing us to customize the lens treatment according to surgeon preference and lens density. The treatment patterns are generally divided into 3 categories: cuts, cylinders, and grids. Cuts can be used to divide the lens into 2, 4, 6, or 8 equal segments. Cylinders can be added to create circumferential ring segments and be increased to form a more complicated spider-web pattern, creating smaller segments to facilitate nuclear removal. A grid pattern creates small cubes of a preprogramed size (approximately 100 to 2000 microns), ultimately subdividing the lens into the smallest possible fragments. These treatment patterns can be combined or used alone, according to the surgeon’s preference for a particular case.

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