Femtosecond laser-assisted cataract surgery for complex cataracts – A review

Abstract

Since its inception in 2009, femtosecond laser-assisted cataract surgery (FLACS) has become an alternative to conventional phacoemulsification cataract surgery (CPCS). Clinical studies were unable to demonstrate superior visual outcomes, but revealed reduced endothelial cell loss. More recently, the cost-effectiveness of FLACS over CPCS in routine cataract surgeries has been challenged. However, the unique abilities of FLACS to customize anterior capsulotomies precisely, soften and fragment the nucleus without capsular bag stress, and create corneal incisions may have special utility in complex cataract and less-common scenarios. In this article, we review the unique role of FLACS in complex cataract surgeries and how it could play a role to improve the safety and predictability of nonroutine cataract surgery.

Cataract surgery is one of the most common surgeries performed worldwide. Since its approval by the US Food and Drug Administration (FDA) in 2010, femtosecond laser-assisted cataract surgery (FLACS) has demonstrated high levels of safety and efficacy.[1] FLACS replaces several steps in conventional phacoemulsification cataract surgery (CPCS), including corneal wound incisions, continuous curvilinear capsulorhexis (CCC), and nucleus fragmentation. FLACS has demonstrated benefits over CPCS, including circular and well-centered capsulotomies,[2] reduced lens tilt and decentration,[3] reduced zonular stress,[4,5] and reduced endothelial cell loss (ECL).[6]

In recent years, however, there have been questions about the cost-effectiveness of FLACS in routine cataract surgery. Two landmark randomized controlled trials (RCTs) – the Femtosecond Laser-Assisted Cataract Surgery Versus Phacoemulsification Cataract Surgery (FACT) and Femtosecond laser-assisted versus phacoemulsification cataract surgery (FEMCAT) studies – have concluded that FLACS is not more cost-effective than CPCS for routine cataracts.[7,8] Furthermore, a recent Cochrane review by Narayan et al.[1] has concluded that there is little or no difference between FLACS and CPCS on the quality of life.

On the other hand, the European Registry of Quality Outcomes for Cataract and Refractive Surgery study of 3379 consecutive eyes demonstrated that FLACS had favorable visual and refractive outcomes when compared to CPCS, while maintaining a low rate of intraoperative capsule complications (14 eyes, 0.4%).[9] Importantly, while early refractive and safety outcomes are commonly reported in comparative studies between FLACS and CPCS, other parameters such as long-term intraocular lens stability (tilt, decentration) and refractive stability are less reported. The latter parameters could be more important in challenging cataract surgeries, where the margin of error is smaller than in routine cataract surgery.

To address this gap, we reviewed the literature from 2009 to 2023 on the role of FLACS in complex cataract surgeries, including its safety and predictability of surgical outcomes. In this review article, we will describe the utility of FLACS in various challenging cataract surgery scenarios and appraise the evidence surrounding these use cases. Specifically, we will discuss the unique advantages (and some caveats) of using FLACS for the following scenarios: 1) compromised corneas, 2) brunescent cataracts, 3) white cataracts, 4) posterior polar cataracts (PPCs), 5) subluxated crystalline lens, 6) prior radial keratotomy (RK), and 7) anterior lenticonus and other indications.

An overview of femtosecond laser for cataract surgery

The femtosecond laser is a near-infrared laser at a wavelength of 1053 nm, which generates ultrashort laser pulses (pulse duration of about 200–800 fs, where 1 fs = 10^-15 s). These ultrashort pulses can apply a highly localized delivery of laser energy within transparent tissues through a mechanism called dielectric breakdown.[10] The photon energy generated ionizes tissue by producing plasma with a temperature between 100°C and 300°C – a process known as photodisruption. Photodisruption creates cavitation bubbles which can rupture tissue without significant collateral damage.[11] With the aid of a microscopic imaging system (e.g., optical coherence tomography [OCT] or Scheimpflug imaging), the femtosecond laser can be precisely focused on a specific depth within the cornea or the lens, thus creating multiple adjacent microcavitation bubbles within 5 µm of accuracy.[11] This results in the typical accompaniment of bubbles in the anterior chamber and truncation of cortex at the capsulotomy rim.

In FLACS, the laser settings could be preprogrammed based on the intended surgical steps: corneal incision including arcuate keratotomy, anterior capsulotomy, and nuclear softening/fragmentation. In each step, laser energy, laser spot size, and laser spot spacing (vertical and horizontal) could be modified to achieve the desired ionization effect at the tissue level. During nucleus fragmentation, different laser segmentation patterns could be selected (e.g., grid vs. pizza pie pattern). With anterior segment OCT (AS-OCT) imaging, the laser could be accurately placed at the appropriate depth (e.g., safety margins from the anterior and posterior capsules), meridian (e.g., for placement of corneal incisions), and size (e.g., sizing and positioning of anterior capsulotomy). Femtosecond laser arcuate keratotomy (FS-AK) is typically done for low to moderate amounts of regular corneal astigmatism.[12] When compared to limbal relaxing incisions, FS-AK has been demonstrated to achieve less postoperative residual cylinder.[13] Therefore, FS-AK is a useful option in countries where low toric power intraocular lenses are unavailable.

Currently, there are five types of commercially available femtosecond laser machines for cataract surgery: Catalys^™ Precision Laser System (Johnson and Johnson Vision Care, Inc., NJ, USA), LENSAR^® Laser System (LENSAR, Inc., FL, USA), LenSx^® Laser System (Alcon Laboratories, Inc., TX, USA), VICTUS^® (Bausch + Lomb, Inc., NY, USA), and Femto LDV Z8 (Ziemer Ophthalmic Systems AG, Switzerland). All machines have similar operational settings [Table 1]. Of note, the Femto LDV Z8 is a low-energy, high-frequency laser, which results in less bubbles intraoperatively. In 2022, the US FDA gave clearance for the ALLY Adaptive Cataract Treatment System (LENSAR, Inc., FL, USA), which is the successor to the LENSAR^® system and combines imaging with their dual-pulse femtosecond laser in a single system.[14]

Table 1.

Overview of existing femtosecond laser system for cataract surgery

		Catalys™ (Johnson and Johnson Vision Care, Inc.)		LENSAR® (LENSAR, Inc.)		LenSx® (Alcon Laboratories, Inc.)		Femto LDV Z8 (Ziemer Ophthalmic Systems AG)		VICTUS® (Bausch + Lomb, Inc.)
FDA approval		2011		2011		2010		2015		2014
Patient interface		Non-applanating two-piece, vacuum docking		Non-applanating two-piece, vacuum docking		Curved-interface one-piece, vacuum docking		Curved applanating two-piece, vacuum docking		Water bath
Pulse frequency
Anterior capsulotomy		120 kHz		80 kHz		50 kHz		1 MHz		Up to 160 kHz
Lens fragmentation		120 kHz		80 kHz		50 kHz		2 MHz		Up to 160 kHz
Pulse duration		600 fs		500 fs		600–800 fs		200–500 fs		400–550 fs
Pulse energy
Anterior capsulotomy		3–30 μJ		7–15 μJ		Up to 15 μJ		<50 nJ, up to 6 μJ		6.8 μJ
Lens fragmentation		3–30 μJ		7–15 μJ		Up to 15 μJ		<50 nJ, up to 6 μJ		7.0 μJ
Capsulotomy duration		~1 s		~2 to 3 s		~3 to 5 s		10–15 s		~2 s
Imaging		3D SD-OCT and image-guided laser		3D ray tracing confocal structural illumination		3D SD-OCT and image-guided laser		Proprietary OCT		3D SD-OCT
IOP rise		10 mmHg		40 mmHg		16 mmHg		30 mmHg		Undisclosed

3D=Three dimensional, IOP=Intraocular pressure, OCT=Optical coherence tomography, SD-OCT=Spectral domain optical coherence tomography

Endothelial compromise

Multiple studies have evaluated the role of FLACS in patients with preexisting corneal compromise, with the most common condition being Fuchs endothelial corneal dystrophy (FECD). Phacoemulsification can result in ECL between 4% and 25%.[15,16] Common surgical factors include ultrasound energy used, duration of phacoemulsification, irrigation fluid, and usage of balanced salt solution.[17,18,19] FLACS allows laser nuclear fragmentation which reduces the surgical duration, ultrasound energy, and irrigation fluid used intraoperatively.[20,21,22] A meta-analysis by Wang et al. showed that compared to CPCS, FLACS results in significantly lower ECL at all time points up to 6 months postoperatively and significantly reduced central corneal thickness (CCT) indicative of faster recovery from corneal edema.[23]

In healthy eyes, though FLACS frequently results in lower ECL when compared to CPCS, there was often no difference in best corrected visual acuity (BCVA) or CCT in these eyes, suggesting that the differences may not be clinically significant.[24,25]

However, the protective role of FLACS on corneal endothelium may be greater in eyes with preexisting corneal compromise. Fan et al.[26] demonstrated in a prospective case series that in patients with mild or moderate FECD, there was significantly greater CCT in patients who had undergone CPCS when compared to FLACS, suggesting persistent corneal edema. In contrast, Krarup et al.’s[6] prospective RCT in 2021 on the LENSAR^® system did not demonstrate a significant difference in CCT, central corneal endothelial cell count, or corrected distance visual acuity between FLACS and CPCS. Recently, a study using Femto LDV Z8 system demonstrated significantly less ECL compared to CPCS in normal eyes at 1 year, but did not demonstrate differences in clinical outcomes and visual acuity.[27]

Separately, Cruz et al.[28] demonstrated that in patients with diabetes and moderate cataracts, FLACS resulted in higher postoperative endothelial cell density when compared to CPCS at 3 months postoperatively, suggesting that there may be a protective role of FLACS in this group of patients as well. Likewise, Kang et al.[29] also demonstrated that there was significantly thinner CCT in diabetics undergoing FLACS compared to CPCS.

A summary of studies on FLACS and ECL in various scenarios is provided in Table 2. Some studies have suggested that the incorporation of laser automated corneal incision could result in greater ECL,[20,30,31,32] while others have not.[24,33,34] Given the lack of standardization of patient profile, femtosecond laser settings, intraoperative surgical techniques, and consistent reported outcomes, the synthesis of these studies is not straightforward. Important intraoperative factors (e.g., frequency and type of ophthalmic viscoelastic device [OVD] replacement, position of phacoemulsification needle in the anterior chamber, presence/extent of lens fragment contact with the corneal endothelial, and amount of intraoperative turbulence) can vary significantly between surgeries and are not easily quantified. While there is consistent evidence that FLACS results in reduced ECL and faster corneal recovery when compared to CPCS, this currently does not translate toward better long-term visual outcomes.

Table 2.

Outcomes of femtosecond laser-assisted cataract surgery on endothelial cell loss

Author		Study design		Sample size (number of eyes)		Laser system		Settings for lens fragmentation		% ECL (duration postoperatively)
Dense cataracts
Chee et al.[35]		Prospective RCT		23		VICTUS®		9.0 μJ, 10 μm spot separation, 16 nuclear segments		9.6% (1 month)
Chee et al.[35]		Prospective RCT		22		VICTUS®		9.0 μJ, 14 μm spot separation, grid pattern of 600 μm		6.5% (1 month)
Chen et al.[36]		Prospective comparative case series		47		LenSx®		Six pieces in a cross pattern		17.2% ± 16.3% (1 day) 13.1% ± 13.1% (1 week) 11.4% ± 12.1% (1 month) 7.6% ± 8.6% (3 months)
Fuchs endothelial corneal dystrophy
Fan et al.[26]		Prospective case series		31		LenSx®		Concentric cylinder and chop (sextant cuts) 5.0 μJ		21.3% ± 9.7% (1 month) 3.6% ± 7.2% (3 months) 3.9% ± 7.9% (6 months) 26.1% ± 8.2% (12 months)
Diabetic
Cruz et al.[28]		Prospective RCT		47		LenSx®		Concentric cylinders and segmental cuts		12.3% (3 months)
Kang et al.[29]		Retrospective comparative case series		31		LenSx®		11 μJ, four radial cuts with a quadrant of rings		6.7% ± 11.5% (1 month) 5.7% ± 9.3% (3 months)
General
Ang et al.[37]		Retrospective case series		296		VICTUS®		8.0 μJ, combined circular (two circles, diameters of 2.0 and 2.8 mm) and four-cut cross-shaped pattern (diameter of 8.0 mm)		6.7% (6 months)
Dzhaber et al.[24]		Prospective RCT		134		LenSx®		7 μJ, 14 μm spot and layer separation, four cylinders		10.7% ± 20.0% (1 month) 11.2% ± 17.9% (3 months)
Krarup et al.[6]		Prospective RCT		81		LENSAR®		“Pie-cut 6” with three concentric circles		12.9% (40 days) 13.6% (180 days)
Liu et al.[27]		Prospective RCT		85		Femto LDV Z8		Six-sector pie-cut pattern at 100% energy		1.5% ± 0.3% (3 months) 7.2% ± 1.9% (6 months) 8.2% ± 2.8% (1 year)
Roberts et al.[25]		Prospective RCT		200		LenSx®		Six segments+one cylinder

ECL=Endothelial cell loss, RCT=randomised controlled trial. ¹Calculated based on average of 28 eyes from a larger case series

Brunescent cataracts

Dense cataracts present challenges to the cataract surgeon due to the need for greater surgical skill, ultrasound energy, and increased surgical duration. A prospective RCT by Chee et al.[35] in 2021 demonstrated that among patients with nuclear opacity grade of 5 or more (Lens Opacities Classification III[38]) undergoing cataract surgery, FLACS resulted in significantly less ECL when compared to CPCS (173 ± 162 vs. 305 ± 201 cells/mm², one-way analysis of variance [ANOVA] with Bonferroni correction) [Table 2].[35] In that study, the VICTUS^® system was used to create nuclear fragmentation using a grid pattern of 600 µm with maximum setting of 9.0 µJ for nucleus fragmentation (14 µm horizontal and vertical spot spacing). However, there was no reduction in effective phacoemulsification time (EPT) during surgery or BCVA at 1 month postoperatively.

Separately, Chen et al.[36] conducted a prospective comparative cohort study between CPCS and FLACS using the LenSx^® system on hard cataracts (graded ≥4 on the Emery–Little classification). Nuclear prefragmentation was performed to obtain six pieces in a cross pattern, and this resulted in significantly lower EPT (12.19 ± 6.10 vs. 19.08 ± 7.13 s, P < 0.001) and significantly reduced ECL at all time points.[36] The same group further investigated the pattern of nuclear fragmentation and concluded that the quadrant pattern (10 µJ, four segments, 5.2 mm diameter, 10 µm spot separation and layer separation) was the most effective in hard cataracts.[39]

White cataracts

The intumescent white cataract is a surgical challenge due to the risks of radial extension during continuous capsulorhexis leading to the dreaded “Argentinian flag sign.” Brazitikos et al.[40] classified white cataracts into three categories using biomicroscopy and A-scan ultrasound features. The study concluded that type I (intumescent, white cataract with liquified cortex and high internal acoustic reflections) had the highest rates of posterior capsular rupture (PCR), while types II (white cataract with a voluminous nucleus and solid white cortex) and III (white cataract with fibrosed anterior capsule and low internal reflections) required greater ultrasound energy. Type I white cataract also had a high risk of anterior capsule rupture, which was as high as 34% (14 of 44 eyes) in their reported case series. Due to the fibrosed anterior capsule, type III white cataract can also be a challenge during capsulorhexis and radial/irregular tears can be common. Similarly, AS-OCT can also be utilized to predict the risks of anterior capsular rupture, as demonstrated separately by Dhami et al.[41] and Titiyal et al.[42]

Before the advent of femtosecond laser, expedient manual continuous circular capsulorhexis (CCC) was paramount to prevent the Argentinian flag. A needle decompression is often performed to reduce intralenticular pressure. Through the simultaneous firing of a circle of laser, FLACS could obviate the risks of complications during manual CCC. Conrad-Hengerer et al.[31] first demonstrated the feasibility of using FLACS to perform laser capsulotomies using the Catalys^® system on 25 eyes. Using the settings of horizontal spot spacing of 5 µm, vertical spot spacing of 10 µm, pulse energy of 4 µJ, and incision depth of 1000 µm, the authors observed that there were residual anterior capsule tags in 12 eyes (48.0%), with an additional two eyes developing anterior capsule tears during phacoemulsification. However, an increased incision depth in this case may not help with the completion of anterior capsulotomy in an intumescent cataract. At the site where the anterior capsule is first struck by the laser, rapid egress of lenticular fluid results in immediate posterior shift of the entire anterior capsule, resulting in the ongoing laser treatment bypassing the rest of the anterior capsule. This is because the laser treatment progresses from within the lens forward, resulting in incomplete capsulotomies.[43]

In contrast, a comparative study by Zhu et al.[44] demonstrated that FLACS resulted in significantly lower incidence of anterior capsule tears compared to CPCS (0% vs. 12.1%). On using the LenSx^® system to create the 5.0-mm laser capsulotomy, there were no anterior capsular tears (0/66 eyes) despite six eyes (9.1%) having incomplete capsulotomies.

However, the surgeon has to be mindful that incomplete capsulotomy may occur in up to one-third of eyes from FLACS.[43,45,46] A comparative study by Titiyal et al. between FLACS and CPCS (n = 40 each) found that the release of white milky fluid during femtosecond laser delivery was significantly associated with an incomplete anterior capsulotomy (19 of 40 eyes, 47.5%).[78] Staining the anterior capsule with trypan blue after femtosecond laser can help identify micro-adhesions; care should be taken to ensure that is no posterior extension in the event of an anterior capsular tear.

In our experience, we recommend the following anterior capsulotomy settings (9 µJ pulse energy, 4 µm vertical spacing, 6 µm horizontal spacing, 600 µm symmetric position above and below the anterior capsule[43]) to ensure that there are reduced chances of micro-adhesions due to incomplete laser penetration. When dealing with the intumescent lens, the energy level is kept to the default settings to maintain a rapid capsulotomy to achieve a complete cut. For the type III white cataract, pulse energy could be increased to 10 µJ to cut through the fibrous bands.[47] During docking, it is recommended to ensure that there is flat docking, and that the OCT scanning of anterior capsule is complete. The levelness of docking could be assessed during the capsulotomy ring scan by AS-OCT.[43] For Morgagnian cataracts, laser nuclear fragmentation should be avoided as there could be an overlap between the anterior capsulotomy and lens fragmentation plan.[43]

Posterior polar cataracts

Phacoemulsification for PPCs is associated with higher rates of intraoperative complications, including PCR, dropped nucleus, and vitreous loss.[48] PPCs have a distinctive onion ring-like appearance, and are commonly associated with either an increased adhesion between the posterior capsule and the posterior polar opacity or a preexisting posterior capsule dehiscence or both. Using AS-OCT, Pujari et al. classified PPCs into distinct categories and identified specific morphologies with high PCR rates (e.g., moth-eaten appearance, conical appearance; both PCR rate 100%) and general morphologies with low PCR rates (hyporeflective areas between the posterior capsule and opacity, PCR rate 2.0%).[79] Several intraoperative maneuvers could help to reduce the risks of PCR and vitreous loss, including creating an adequately sized capsulorhexis, using the cross-chop technique (for dense nuclei), utilizing reduced phacoemulsification settings, and judicious OVD replacement during instrument withdrawal.[49,50]

To this end, FLACS has demonstrated utility against PPCs. In one of the first case series reported, Alder and Donaldson[51] reported that FLACS resulted in PCR in two patients with bilateral PPC, while CPCS did not in the fellow eye, suggesting that CPCS was the preferred approach in this group of complex cases. In that study, they used the Catalys^™ system and adjusted for a 500-µm safety zone during lens fragmentation to minimize the risk of posterior capsule implication. However, the authors opted to perform hydrodissection during FLACS (while it was avoided during CPCS).[51]

In contrast, subsequent studies identified the helpful role of FLACS in preventing PCR in PPC.[42,52,53,54] In particular, Vasavada et al.[54] described a technique of using femtodelineation to create multiple sharply demarcated layers of cylindrical nuclear fragments which act as mechanical fragments that could reduce PCR rates. In this study, they used the LenSx^® system to create three distinct layers of demarcation from the center of the nucleus, with at least 500 µm from the posterior capsule based on the OCT view. The cylindrical nuclear fragments are removed from the innermost layer outward, leaving behind an epinuclear layer, which is removed last. The authors also reduced the ultrasound energy to between 10% and 20% for the final epinuclear layer (Centurion Vision System, Alcon Laboratories, Inc.). These settings helped to reduce the PCR rate to 4%, compared to previously published rates of 26%–32%.[48,55]

In the same year, Titiyal et al.[42] described a technique where block-by-block emulsification of the prechopped nuclear fragments centrifugally helped to prevent PCRs in PPCs completely, while avoiding manual hydrodissection and hydrodelineation. Using the LenSx^® system, an 800-µm posterior offset was used to minimize disruption to the posterior capsule. The authors also avoided hydrodissection and hydrodelineation during the surgery; the lens fragments were separated through the precut planes and rotation was minimized.

On the Catalys^™ system, Sachdev et al.[53] have utilized a posterior offset of at least 1000 µm from the posterior capsule to enable a thick epinuclear fragment to act as a buffer between the nucleus and the sometimes deficient posterior capsule. In their case series, five of 50 eyes (10%) developed an intraoperative PCR.

In our practice, we avoid hydrodissection regardless of whether femtosecond laser was used for PPC or not; instead, a partial viscodissection at the equatorial plane is preferred to prevent inadvertent disruption of the posterior capsule. We also use AS-OCT to identify any preexisting posterior capsule dehiscence or herniation of lens material. The posterior offset for nucleotomy is kept at 500 µm, unless the polar opacity is huge or there has been a spontaneous posterior capsule defect, which could be detected on either the slit-lamp biomicroscope or AS-OCT [Fig. 1].

Figure 1.

Femtosecond laser adjustment for ruptured posterior polar cataract. In this cataract with a spontaneously ruptured posterior capsule (yellow arrowhead), an increased posterior offset for nucleotomy was achieved by manually shifting the posterior scanned capsule on the femtosecond laser interface (yellow arrows)

Subluxated crystalline lens

The subluxated crystalline lens could be one of the most difficult cataract surgeries for the anterior segment surgeon.[56] The reduced zonular support leads to absent countertraction during manual CCC and a risk of anterior capsule runout in the quadrants of zonular deficiency. Capsular stabilization devices such as the capsule retractors (MicroSurgical Technology, WA, USA) and capsular tension segments (MORCHER^® Ahmed Segment; FCI Ophthalmics, MA, USA) have reduced the risks of capsular runouts, but are technically challenging and time-consuming. Preexisting vitreous in the anterior chamber may lead to difficulty with nuclear fragment removal and sometimes iatrogenic retinal breaks for the unsuspecting cataract surgeon. Intraoperative manipulation during nucleus disassembly with the phacoemulsification needle could further zonular dehiscence and lead to a dropped nucleus.

As the femtosecond laser does not depend on zonular support for capsulotomy, it has definite utility for the subluxated cataract. Chee et al.[57] have previously published a retrospective case series of consecutive cases of subluxated cataracts with at least six clock hours of zonular weakness treated with FLACS through the VICTUS^® system. With FLACS, a lens-centered capsulotomy could ensure a consistent and adequately sized capsule opening, which might otherwise be difficult to achieve with manual capsulorhexis [Fig. 2].[57] The capability of AS-OCT to scan the entire capsule and subsequently center the capsule opening is a unique advantage of FLACS anterior capsulotomy over manual capsulorhexis. Higher energy settings (e.g. 10 µJ) and deeper incision depth (e.g., 1000 µm) may ensure a complete capsulotomy.[58] By pre-softening the nucleus, femtosecond laser for nucleotomy can also reduce zonular stress during phacoemulsification.[59,60]

Figure 2.

Femtosecond laser adjustment for subluxated crystalline lens. After scanning the anterior capsule, the scanned capsule option (yellow circle) was selected to center the femtosecond laser capsulotomy over the capsule instead of over the pupil

However, not all eyes with subluxated crystalline lens may be suitable for FLACS, with notable exclusions that include severely tilted or posterior displaced cataracts which exceed the acceptable limit of the femtosecond laser system, or a lens which is below the minimum required anterior chamber depth for capsulotomy (1.5 mm for the VICTUS^® system). Successful FLACS in patients with severely subluxated crystalline lens have also been reported on the LenSx^® system.[5,61] In 2018, a comparative interventional case series of eyes with severe lens subluxation undergoing FLACS or CPCS showed a better uncorrected visual acuity, lower higher-order aberrations, and lower complication rates with the FLACS group.[62] In 2018, Malyugin et al.[63] described a novel technique to mobilize a pupillary expansion device (Malyugin Ring 2.0; Microsurgical Technology, Inc., WA, USA) fixated with a double-armed 10-0 polypropylene suture (Mani, Inc.) and centered over a subluxated lens in patients with lens ectopia, followed by femtosecond laser lens-centered anterior capsulotomy using the LenSx^® system (3.5–4.8 mm, 110% power, 50.0 mm/s.

Prior RK

Some surgeons have attempted to perform FLACS on eyes with prior RKs. Eyes with previous RKs have increased risks of wound dehiscence during phacoemulsification. Noristani et al.[64] first described FLACS on six RK eyes successfully on the Catalys^™ system (capsulotomy settings: pulse energy 5 µJ, horizontal spot spacing 5 µm, vertical spot spacing 15 µm) and placed primary and site-port positions between the RK incisions. With the above settings, they reported no intraoperative or postoperative complications.

However, more recent studies by Trinh et al.[65] and Friehmann and Assia[66] had less-favorable recommendations. In Trinh et al.’s[65] study on the Catalys^™ system (pulse energy 4 µJ, horizontal spot spacing 4 µm, vertical spot spacing 9 µm), two of 16 eyes (12.5%) developed intraoperative anterior capsule tears. In another retrospective review by Friehmann and Assia[66] also using the Catalys^™ system, three of six eyes (50.0%) had incomplete anterior capsulotomies when routine settings were used (pulse energy 4 µJ, incision depth 500 µm).[66] When the pulse energy was doubled (i.e., 8 µJ) or both pulse energy and incision depth were doubled (i.e., 8 µJ and 1000 µm, respectively), all capsulotomies (five of five eyes) were completed successfully.[66]

The presence of RK incisions may lead to corneal scars, which, in turn, interfere with the scanning of anterior capsule and femtosecond laser application, thus increasing the risks of incomplete capsulotomy. Therefore, we recommend increasing the settings of incision depth and power to maximize the chances of complete capsulotomy. Before removing anterior capsulotomy, the anterior capsule should be stained with trypan blue to look for residual tags and bridges, which should be manually removed to prevent radial tears. There were no reports of wound gape from laser corneal incisions, though we would avoid placing these incisions along the meridians involving the RK incisions to minimize the risks of inadvertent wound dehiscence during phacoemulsification. If necessary, more peripheral corneal or manual corneoscleral incisions may be considered instead.

Anterior lenticonus and other indications

In another related but less commonly encountered scenario, anterior lenticonus is an uncommon condition, typically associated with Alport syndrome. Due to the anterior curvature of the anterior lens capsule resulting in a “pyramidal cataract,” there is a greater risk of capsular runoff during manual capsulorhexis.[67] In addition, Boss and McDermott[67] previously described a “cogwheel-like” ripping of the anterior capsule due to areas of vertical dehiscence every 3–10 µm during manual capsulorhexis. The difficulty is compounded by the greater elasticity of the lens capsule in younger patients. Therefore, a uniform capsulotomy created through FLACS could obviate this challenge and improve the safety of cataract surgery in these younger patients.

Some authors have described FLACS for anterior lenticonus through separate case reports.[68,69,70,71,72,73] Using the LenSx^® system, Ecsedy et al.[69] created a 4.8-mm anterior capsulotomy using a pulse energy of 5 µJ with 4 µm spot separation and 3 µm layer separation. On scanning electron microscopy, there was a uniform serrated profile created through the capsule.

There are other considerations in a pediatric cataract, including the extra elastic lens capsules, frequent need for primary posterior capsulotomy, and postoperative capsular phimosis.[74] Karas et al.[72] described performing anterior capsulotomy using the LenSx^® system (4.8 mm capsulotomy size, 5 µJ pulse energy) on a 6-year-old child with anterior polar cataract. Elsewhere, Dick et al.[75] and Dick and Schultz[76] performed posterior capsulotomies on children using the Catalys^™ system (incision depth 800–1000 µm, diameter between 3.2 and 4.7 mm, pulse energy 8–10 µJ). It should be noted that posterior capsulotomy requires additional steps: suturing the main wound with 11-0 nylon and using an age-dependent correction formula for capsulotomy sizing (Bochum formula).[75]

Postoperative capsular phimosis could also be addressed with the femtosecond laser by focusing directly on the anterior capsule to create the enlarged anterior capsulotomy.[77]

Conclusion

In this review article, we reviewed the continuing role of FLACS in complex cataract surgeries. Even though there have been questions about the cost-effectiveness of FLACS in standard phacoemulsification, there is no doubt that FLACS continues to provide additional safety and predictability in challenging scenarios.

Financial support and sponsorship:

Nil.

Conflicts of interest:

There are no conflicts of interest.