28 Pitfalls: Femtosecond Laser–Induced Complications

Gerd U. Auffarth, Hyeck-Soo Son, and Branka Gavrilovic

Keywords: femtosecond laser, interface, gas development, capsular tears, posterior capsule rupture, learning curve, complications

28.1 Introduction

Cataract surgery is the most widely performed intraocular surgical procedure. Anterior capsulotomy and phacoemulsification constitute fundamental steps of cataract surgery as their quality influences the surgical outcomes and complication rates. ^{1,​ 2,​ 3} Although experienced surgeons can readily achieve high success rate with precision and low rates of complication, cataract surgery still remains a daunting task to trainees and inexperienced surgeons, for whom detrimental complications are not uncommon. Continuous advances in technology and increase in patients’ expectations regarding better visual and safety outcomes led to development of novel medical devices such as femtosecond lasers (Fs-Lasers), which have been successfully implemented since the beginning of the 21st century and are noted to attain great accuracy and safety profile. ^{1,​ 2,​ 3,​ 4,​ 5,​ 6} Previous reports evaluating their performances show evidence of better precision, reproducibility, and refractive outcomes after anterior capsulotomy performed by Fs-Lasers compared to manual cataract surgery. ^{1,​ 3,​ 7,​ 8} Furthermore, Fs-Lasers lead to fewer cases of postoperative intraocular lens (IOL) decentration and tilt, rendering a more reliable and predictable positioning of the IOL possible. ⁷

Nevertheless, despite the initial promising results, the reported benefits of Fs-Laser necessitate that a surgeon undergoes an adequate familiarization and clinical experience with the technology.

28.1.1 The Learning curve

In a prospective case series, Roberts et al studied 1,500 eyes undergoing femtosecond laser–assisted cataract surgery (FLACS) and divided the cases into two groups, the first group comprising the first 200 cases during which the surgeons are initially exposed to the Fs-Laser system and the second group consisting of the subsequent 1,300 cases during which the surgeons are assumed to be experienced. ¹ When a comparison was made, the complication rates decreased significantly in the second group than the first group, with the rates of major capsular complications such as anterior tears decreasing from 4 to 0.31%, posterior tears from 3.5 to 0.31%, and posterior lens dislocations from 2 to 0%. ▶ Table 28.1 shows a comparison of the intraoperative complication rates between the two groups.

Initial lens docking also posed a technical difficulty requiring adapted dexterity as suboptimal lens alignment led to incomplete capsulotomies or peripheral suction loss (▶ Fig. 28.1, ▶ Fig. 28.2). It is important to further note the possible problems associated with the docking system such as presence of any ocular surface pathologies that may interfere with the penetration of the laser beam or potential aggravation of pre-existing conditions, that is, glaucoma or optic neuropathy, through application of the docking pressure. ⁹ In the second group, Roberts et al found a decrease in number of docking attempts from 1.5 to 1.05 per case and in rates of suction breaks hindering laser corneal incisions from 2.5 to 0.61%, ultimately advocating the true safety and efficacy of the laser system after the surgeons have become familiar with the procedure. ¹

These results are comparable to the outcomes analyzed by Bali et al, ⁴ who conducted a prospective, consecutive cohort study with the first 200 eyes undergoing Fs-Laser cataract surgery and divided the cases into four consecutive groups of 50 cases to evaluate the learning curve of the surgeons. Despite the high rates of complication in the initial cases, the authors established a clear learning curve and found a rapid and significant reduction in numbers of docking attempts, cases of miosis after the laser procedure, and free-floating capsulotomies after experience. ▶ Table 28.2 demonstrates a comparison of the number of complications during laser and phacoemulsification procedures in the four consecutive groups.

Besides the reduction in intraoperative complication rates and evident learning curve associated with the usage of the Fs-Laser, pretreatment with laser before the cataract surgery was also found to significantly decrease the overall phacoemulsification time. Abell et al found that when cataract was pretreated with laser, the mean effective phacoemulsification time (EPT) showed a statistically significant reduction of 84% for all cataract grades, with more than 57% of cases showing a mean EPT of fewer than 2 seconds and 80% of cases having a mean EPT of fewer than 4 seconds. ^{8,​ 10} The authors also demonstrated that a reduction of EPT to even zero can be realized if the operation is conducted by an experienced surgeon who is both familiar with the laser treatment, lens fragmentation techniques, and phacoemulsification parameters. Less amount of phacoemulsification energy spent is associated with a decrease in postoperative corneal edema and corneal endothelial cell loss, which in turn increase the overall safety profile of the Fs-Laser pretreatment and lead to earlier visual recovery.

The high accuracy and reproducibility of the Fs-Laser system have been widely confirmed by numerous clinical studies. ^{1,​ 3,​ 4,​ 5,​ 7,​ 8} Successful completion of a laser pretreatment before cataract surgery can lead to more stable capsulotomy, reduced EPT, as well as faster visual recovery. Yet, as the usage of the laser system involves a definite learning curve, sufficient amount of time must be spent to gain experience before achieving complication rates comparable with the best published reports of manual cataract surgery.

28.2 Technical Aspect

28.2.1 Docking Procedure

The connection of the Fs-Laser with the patient’s eye is done through an interface that can be applied in different ways. Some Fs-Lasers are connected by placing a suction ring on the patient eye and adding a liquid or soft interface. Some lasers are connected by direct contact onto the cornea or with an interface with a special contact lens. This process can be complicated by a narrow orbit, a compromised lid opening, suction loss during laser application, or conjunctival bleeding because of the suction ring.

Nagy et al found in a retrospective analysis of the first 100 FLACS intraoperative complications including suction break (2%), conjunctival redness, or hemorrhage (34%). ⁵ After the patient interface was improved, suction break did not recur. Patient’s head or eye movement, improper docking, and loose conjunctiva are discussed as main risk factors for suction break. Precise patient interface placement and good preoperative anesthesia are the most important factors in preventing suction break. Finally, the authors advise usage of a hard headrest instead of a soft headrest, which can push the patient’s head down during insertion of the patient interface, causing suction loss. ⁵

Schultz et al reported the patient moved her head abruptly during lens fragmentation, which led to suction loss, but the laser continued firing for a fraction of a second. An IOL was implanted without complications. Although the patient achieved visual acuity of 20/20 6 weeks after the surgery, suction loss at other point of time during laser treatment such as during capsulotomy may result in incomplete cutting and more serious complications. ¹¹

In a prospective, consecutive cohort study of Bali et al, the first 200 eyes were undergoing laser cataract surgery (LCS) with the object of reporting the intraoperative complications. ⁴ At the end, the authors noted an initial difficulty while docking the system onto the patient’s eye that led to 5 cases of suction loss. Though there was no impact in the surgical procedure or the final outcome, docking of the lens may create an inconvenience for inexperienced surgeons who are not yet familiar with the suction fixation device. ¹²

The comparison of liquid immersion interface with contact corneal applanation during the docking stage of the laser treatment was studied by Talamo et al. They found that a curved contact can lead to incomplete capsulotomy formation during the laser treatment due to corneal folds. A liquid interface eliminated corneal folds, improved globe stability, and allowed a lower intraocular pressure (IOP) rise and reduced subconjunctival hemorrhage. ¹³

28.2.2 Complication of Capsulotomy

Early laboratory studies mostly using porcine eyes concluded that the Fs-Laser capsulotomy is at least equal or even stronger that conventional manual capsulotomies. ¹⁴ More recent studies especially in humans indicate possible weakness of capsulectomy edges. ^{15,​ 16,​ 17,​ 18}

Abell et al ¹⁹ studied in a prospective, comparative cohort case series of 1,626 patients undergoing LCS or phacoemulsification to compare the incidence of anterior capsule tears. They found that there was a significantly higher rate of anterior capsule tears in the LCS group (15/804, 1.87%) than phacoemulsification cataract surgery group (1/822, 0.12%). In 7 cases, the anterior capsule tear extended to the posterior capsule. Thus, the conclusion is that laser anterior capsulotomy integrity seems to be compromised by postage-stamp perforations and additional aberrant pulses, possibly because of fixational eye movements. This can lead to an increased rate of anterior capsule tears, and extra care should be taken during surgery after Fs-Laser pretreatment has been performed. ⁸

In a retrospective case series of 170 eyes that received anterior capsulotomy or combined anterior capsulotomy and lens fragmentation using a noncontact Fs-Laser system (LensAR) before phacoemulsification, Chang et al ⁶ had the following results: 151 eyes (88.8%) had free-floating capsule buttons; 9 eyes (5.3%) had radial anterior capsule tear that did not extend to the equator or posterior capsule; and 1 eye (0.6%) had a posterior capsule tear.

Nagy et al found in their retrospective analysis of the first 100 LCS intraoperative complications capsule tags and bridges (20%) and anterior tears (4%). ⁵

Kohnen et al tried to examine the morphological changes in the edge structure of Fs-Laser-derived capsulotomy specimens using varying patient interfaces and different laser pulse energies. In their study, Fs-Laser-assisted capsulotomies were performed in 30 eyes using the LenSx Fs-Laser. Surgery was performed using either a rigid curved contact interface (group 1, 15 eyes) or a curved interface with a soft contact lens between cornea and interface (group 2, 15 eyes). The laser pulse energy was set to 15 μJ in group 1 and to 5 μJ in group 2. ¹⁵

Light microscopy showed continuous anterior capsular incisions with a prominent demarcation line along the cutting edge, as well as tags and bridges, which were more pronounced in group 1. They concluded that a soft contact lens interface with a subsequent laser pulse energy of 5 μJ resulted in fewer tags and bridges, smoother edges, and a more regular and thinner demarcation line on specimen edges of Fs-Laser-performed capsulotomies compared to a rigid curved 15-μJ interface application.

Sándor et al compared the mechanical properties of anterior capsule opening performed with Fs-Laser capsulotomy at different energy settings in ex vivo porcine anterior lens capsule specimens. They performed the capsulotomies with three different pulse energy levels: 2 µJ (low-energy group), 5 µJ (intermediate-energy group), and 10 µJ (high-energy group). The capsule openings were stretched with universal testing equipment until they ruptured. The morphologic profile of the cut capsule edges was evaluated using scanning electron microscopy. The high-energy group had significantly lower rupture force (108 ± 14 mN) compared to the intermediate-energy group (118 ± 10 mN; p < 0.05) and low-energy group (119 ± 11 mN; p < 0.05), but the difference between the intermediate-energy and low-energy groups was not significant (p = 0.9479). They concluded that anterior capsule openings created at a high-energy level were slightly weaker and less extensible than those created at low or intermediate levels, possibly due to the increased thermal effect of photodisruption. ²⁰

28.2.3 Gas Breakthrough/Capsular Block Syndrome

During laser treatment, the gas bubbles can compromise the laser energy (▶ Fig. 28.3) resulting in capsulotomy tearing or as a positive impact create a kind of pneumodissection (▶ Fig. 28.4).

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