Femtosecond Laser-Assisted Cataract Surgery
John P. Berdahl
Justin A. Schweitzer
Adam R. Bleeker
Since its inception in the early 1980s, the neodymium-doped yttrium aluminum garnet (Nd:YAG) laser has played a pivotal role in clinical eye care. Its revolutionary nanosecond (10-9) pulse rate allowed surgeon’s to treat ocular pathology noninvasively with safe and predictable results. However, the Nd:YAG laser lacked precision, preventing its use in corneal and refractive procedures.
In 1990, Dr. Juhasz and his colleagues at the University of Michigan College of Engineering Center for Ultra-fast Optical Sciences developed a means of shortening the pulse duration of the Nd:YAG laser from the nanosecond (10-9) to femtosecond (10-15) range.1 This decreased energy output and increased peak intensity, leading to micron precision and less surrounding tissue injury.2 In 2008, Nagy et al. described the use of the femtosecond laser during cataract surgery.3 Initial outcomes were promising as all anterior capsulotomies were appropriately sized/centered, and laser-assisted lens fragmentation resulted in less overall phacoemulsification time.3 By 2010, the procedure known as femtosecond laser-assisted cataract surgery (FLACS) had received approval from the United States Food and Drug Administration (FDA).4
While conventional cataract surgery is safe and effective, there remains room for improvement. The femtosecond laser replaces several of the manual steps of cataract surgery, with the goal of improving safety and reproducibility. However, its implementation into primary ophthalmologic care has been slow due to the ongoing debate regarding its advantages over traditional phacoemulsification techniques. Nonetheless, it remains a viable option for ophthalmology practices seeking to offer premium refractive cataract surgery.
INDICATIONS
Key Indications
Anterior capsulotomy
Lens fragmentation and liquefaction
Corneal incisions
Astigmatic keratotomy
Anterior Capsulotomy
Creating a continuous circular capsulorhexis is one of the more difficult aspects of traditional cataract surgery. If the capsulorhexis is too large, the intraocular lens (IOL) implant can tilt or decenter, producing posterior capsule opacification and greater higher-order aberrations. If the capsulorhexis is too small, the IOL can shift posteriorly, resulting in hyperopic shift and capsular phimosis.5 A properly centered and sized capsulorhexis is essential for successful refractive outcomes.
Although skilled surgeon’s generate consistent results, anterior capsulotomies cut by the femtosecond laser have demonstrated less deviation in size, superior centration, and greater circularity (Figure 16.1).5 There is, however, disagreement regarding the safety of laser-assisted anterior capsulotomy. Two small prospective studies evaluating the safety of laser-assisted anterior capsulotomy demonstrated a similar number of adverse events, compared with manual capsulotomy.5,6 Yet meta-analysis data suggest that capsular tears and tags may be more common than initially reported.4 Despite this discordance, laser-assisted capsulotomy is a step toward a safer and more standardized approach.
Lens Liquefaction and Fragmentation
At present, phacoemulsification is the standard of care for cataract extraction. Over the past half-century, the safety of phacoemulsification has greatly improved, yet corneal endothelial cell loss and posterior capsular rupture still occur. The femtosecond laser seeks to alleviate these risks, given its micron precision and reliability.
Lens fragmentation occurs through a complex set of molecular reactions (Figure 16.1). Femtosecond laser energy gives rise to free electrons and ionized molecules, which, in turn, create a rapidly expanding wave of plasma. Similar to an acoustic shock wave, this plasma liquifies and dissects through optically transparent tissue.7 For patients with softer cataracts, central liquification of the opacified lens is recommended. As nuclear sclerosis progresses, a hybrid pattern consisting of central liquification and peripheral fragmentation is favored.7 Various sequences have been developed for the purpose of reducing phacoemulsification time and corneal endothelial cell loss.8 Therefore, as surgeon’s push for zero effective phacoemulsification time, the femtosecond laser presents one possible solution.6,8
Corneal Incisions
Irregular corneal wounds are more susceptible to aqueous leak, infection, and surgically induced astigmatism (SIA).7 Historically, clear corneal incisions pass along a single plane, creating an opportunity for bacteria to enter the eye and often requiring stromal hydration at the end of the case.7 Laser-assisted corneal incisions are highly customizable, theoretically reducing the complication risk. The femtosecond laser offers multiplanar, trapezoid wounds, which demonstrate better integrity and predictability (Figure 16.1).9 Yet like traditional cataract surgery, laser-assisted corneal incisions result in SIA and higher-order aberrations.10 The rate of SIA correlates directly with docking issues and tends to decrease with experience.
 FIGURE 16-1 FLACS laser sequence. (a) 360 capsulorhexis, (b) lens fragmentation, (c) arcuate incisions, and (d) clear corneal incisions. |
Astigmatic Keratotomy
Between 33% and 50% of eyes possess one diopter of corneal astigmatism at the time of cataract surgery.11 An armamentarium of surgical options exists for astigmatism correction, including toric IOLs, astigmatic keratotomy (AK), limbal relaxing incisions, and light-adjustable IOLs. Femtosecond laser-assisted AK possesses many advantages over manual incisional techniques (Figure 16.1). Traditional AK incisions are open, placing eyes at risk for scarring and infection along the visual axis.
Femtosecond laser-assisted AK incisions are intrastromal, reducing the risk of postoperative infection and pain. Though adverse outcomes have been reported, laserassisted AK is a safe and effective treatment for astigmatism, which can be completed at the time of cataract surgery.11,12
Femtosecond laser-assisted AK incisions are intrastromal, reducing the risk of postoperative infection and pain. Though adverse outcomes have been reported, laserassisted AK is a safe and effective treatment for astigmatism, which can be completed at the time of cataract surgery.11,12
CONTRAINDICATIONS
Key Contraindications
Small, non-dilating pupil (relative)
The only relative contraindication to FLACS is a small, non-dilating pupil.7 Pupil dilation is measured preoperatively and should be greater than 6.0 mm. While laser-assisted anterior capsulotomy is possible with a pupil diameter less than 6.0 mm, there is increased risk of injury to the iris (Figure 16.2). Furthermore, if an already small pupil experiences intraoperative miosis following laser pretreatment, subsequent phacoemulsification and lens extraction can be challenging. The size of anterior capsulotomy can be adjusted to accommodate for a small, non-dilating pupil. However, smaller anterior capsulotomies (i.e., less than 4.0 mm in diameter) are at increased risk of capsular phimosis.
INFORMED CONSENT CONSIDERATIONS
Key Informed Consent Adverse Events
Complications of ocular surgery may include blindness, double vision, loss of corneal clarity, infection, iritis, droopy eyelid, glaucoma, hyphema, pupillary dysfunction, lens dislocation, loss of eye, retinal swelling, and retinal detachment.
Complications due to anesthesia or drug reactions of other factors may involve other parts of the body, including the possibility of brain damage or even death.
Complications for presbyopia correction include halos, ghost images, night glare, double vision, blurry vision, trouble with depth perception, trouble with nighttime driving, and glasses may still be needed.
The introduction of several new technologies in the cataract surgery space has led to an increased importance of the informed consent process. In order to reduce medicolegal risk associated with cataract surgery, it is important to manage patient
expectations and have documents that support it. The informed consent is intended to promote patient safety and reduce liability exposure when cataract surgery is performed. The decision to proceed with cataract surgery is acceptable once the informed consent process has been shown to be well documented in the patients’ medical record, and the risk/benefits of the procedure are documented on the informed consent.
expectations and have documents that support it. The informed consent is intended to promote patient safety and reduce liability exposure when cataract surgery is performed. The decision to proceed with cataract surgery is acceptable once the informed consent process has been shown to be well documented in the patients’ medical record, and the risk/benefits of the procedure are documented on the informed consent.
 FIGURE 16-2 Poor dilation is a relative contraindication for FLACS. In the example cited earlier, a 4.7-mm diameter capsulorhexis was cut due to poor dilation. |
PREOPERATIVE EVALUATION
Key Preoperative Considerations
Dilated slit lamp and fundus exam assessing for indications and contraindications
Preoperative drops: cyclopentolate 1%, phenylephrine 10%, ketorolac 0.5%, and tropicamide 1%
A standard cataract evaluation is required prior to FLACS. This includes a thorough review of the patient’s past medical and surgical history. Notably, patients with dry eye may experience worsening of symptoms after FLACS.13 Thus, treating the ocular surface before the procedure is important. This can be achieved in a variety of ways, including artificial tears, topical pharmaceutical agents, punctal plugs, meibomian gland treatments, and nutraceuticals. An algorithm for the treatment of dry eye prior to cataract surgery has been described elsewhere.14 Current medications should also be reviewed as blood thinners may compound the intraoperative bleeding risk. However, discontinuation of these medications is not required.
Visual acuities, manifest refraction, and glare testing are useful in determining the visual significance of the cataract. Undilated slit lamp examination of the anterior segment provides an overall health assessment. Dilated fundus examination establishes baseline vitreoretinal disease and helps to assess pupillary dilation. Surgical planning is completed following ocular biometry, optical coherence tomography, and corneal topography, which aid in selection of the IOL and calibration of the femtosecond laser. On the day of surgery, mydriasis is achieved via the instillation of either of a combination of cyclopentolate 1%, phenylephrine 10%, ketorolac 0.5%, and/or tropicamide 1%.
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