24 Femtosecond Laser–Assisted Cataract Surgery in Ocular Comorbidities

Surendra Basti and Rushi K. Talati

Keywords: Femtosecond laser cataract surgery, FLACS, complex cataracts, femtolaser, subluxed cataract, posterior polar cataract

24.1 Introduction

As with almost any new medical advances, femtosecond laser–assisted cataract surgery (FLACS) was at first used in so-called “routine cases.” The recognition that FLACS is able to provide predictable, localized tissue disruption suggests that it may be advantageous in high-risk, complex clinical cases. This has indeed been borne out as evidenced by the increasing number of reports alluding to the use of femtosecond lasers in patients with heterogeneous ocular features. ^{1,​ 2,​ 3,​ 4,​ 5,​ 6,​ 7,​ 8,​ 9,​ 10}

This chapter reviews reported experiences in eyes with ocular comorbidities. While most of these are case reports or short case series, they provide a glimpse of how the capabilities of femtosecond laser technology can be extended to successfully treat such cases. There is every reason to believe that innovation with laser technology has just begun and that there will be more to come.

24.2 Patient Selection

Before considering applications of the femtosecond laser in cataract surgery in patients with comorbid conditions, it is useful to review the characteristics that are traditionally considered suboptimal for FLACS:

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  Pupil that will not dilate to at least 5.0 mm.

  
  
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  Corneal opacity precluding the effective transmission of laser energy.

  
  
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  Advanced glaucoma with a tenuous optic nerve.

  
  
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  An uncooperative or overly anxious patient.

  
  
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  Small interpalpebral fissures that may interfere with secure docking of the laser.

Exclusion criteria are constantly being revised and updated as femtosecond laser technology continues to improve and surgeons gain experience in its use. In the sections that follow, we will discuss novel approaches that have adapted FLACS to various patient comorbidities, frequently achieving superior outcomes to manual phacoemulsification.

24.3 Zonular Instability

A patient group that may especially benefit from the femtosecond laser includes patients with weak zonules, such as those with pseudoexfoliation, Marfan’s syndrome, or eyes that develop cataracts and zonular rupture following trauma. Zonular weakness is a significant risk factor for complications during cataract surgery and should be carefully assessed preoperatively. Direct signs include lens subluxation, absent or sparse zonules as evidenced by straightening of the lens equator, iridodonesis, or phacodonesis. Additionally, advanced age, the presence of a shallow, uneven, or hyperdeep anterior chamber (AC), and reduced pupil size are frequently indirect clinical predictors of zonular instability.

24.3.1 Surgical Challenges

Zonular weakness presents a unique array of challenges during surgery. Reduction in the anterior capsular tension increases the force required to pierce the capsule when forming the capsulorhexis. ¹¹ Furthermore, correcting an errant capsulorhexis is more difficult in the absence of zonular countertraction. Zonular rupture may also occur secondary to routine maneuvers required to divide and rotate lens fragments. ¹¹

The femtosecond laser offers clear benefit for patients with zonular weakness, as the laser is not dependent on zonular countertraction to create a capsulotomy. Also, the ability to position the capsulotomy as desired with FLACS permits centering the capsulotomy on the capsular bag even in eyes with a partially displaced lens.

24.3.2 Reported Evidence

Initial clinical experience underscores the advantages of the laser in eyes with zonular weakness. Grewal and colleagues reported a patient with a traumatic subluxated cataract who underwent FLACS and described the intraoperative surgical modifications and advantages of FLACS. ⁴ There were nearly 5 clock hours of zonular dialysis with lens subluxation and a traumatic cataract after blunt ocular trauma. A 5-mm capsulotomy diameter was selected and, using intraoperative imaging and the custom capsulotomy setting, this was centered on the capsular bag, and not on the pupil margin. The pulse energy was maximized to 10 µJ and the incision depth increased to 1,000 μm. ⁴ Lens fragmentation was performed using the sextant pattern. No lens softening was performed, and the subluxated lens was stable during FLACS docking and laser delivery. ⁴ FLACS allowed creation of a circular capsulotomy centered on the capsular bag, thus permitting use of capsular-support hooks and nuclear removal before insertion of the capsular tension ring (▶ Fig. 24.1). Unique to the femtosecond laser is its ability to create a capsulotomy and segment the lens in a closed chamber, further minimizing intraocular manipulation during the subsequent steps of cataract surgery. In this case, laser segmentation permitted removal of lens sextants with relative ease, minimizing zonular stress during phacoemulsification (▶ Fig. 24.1).

Schultz and colleagues described the use of the femtosecond laser for capsulotomy in a subluxated lens in a 10-year-old patient with Marfan’s syndrome. ⁵ The capsulotomy was free floating and could be performed within a completely visible area. The well-centered laser capsulotomy paved the way for subsequent aspiration of the soft lens with standard bimanual irrigation and aspiration devices, the use of a capsular tension ring (Cionni ring type 1L, Morcher, Stuttgart, Germany), and finally intraocular lens (IOL) implantation without decentration. ⁵ More recently, Crema and colleagues report successful FLACS in three eyes with mild, moderate, and severe lens subluxation. ¹² In the mildly subluxed eye, a routine 4.8-mm-diameter capsulotomy was performed and manually centered on the subluxed lens using a free positioning setting (LenSx laser, Alcon Laboratories, Fortworth, TX). A hybrid lens fragmentation pattern with two 4.7-mm crosslines and one 2.0-mm-diameter cylinder was then applied. In the moderately subluxed eye, the capsulotomy was sized to 4.6 mm to allow for satisfactory positioning. Lens fragmentation was adjusted to two 4.5-mm crosslines and one 2.0-mm-diameter cylinder. The most severely subluxed eye received a 3.5-mm capsulotomy, two 3.6-mm crosslines, and one 2.0-mm-diameter cylinder for lens fragmentation. The mild and moderately subluxed eyes also received corneal intrastromal relaxing incisions to decrease corneal astigmatism. No complications were encountered and all three eyes achieved uncorrected distance visual acuity of 20/25 or better, stable through 12 months of follow-up. ¹²

Use of FLACS has been described in several posttrauma situations such as corneal penetrating injury, ⁶ lens capsular damage, ^{2,​ 3} and white traumatic cataracts following blunt trauma. ³ Szepessy and colleagues reported successful use of the femtosecond laser in a case of traumatic cataract. ⁶ A 38-year-old man had a penetrating eye injury from a wire. The corneal laceration was sutured first. In the postoperative period, he developed a cortical cataract and there was an area of rupture of the anterior capsule. Two weeks after primary repair, cataract surgery was performed using the LenSx laser. The area of anterior capsular rupture was included in the capsulotomy created by the laser, thus achieving an intact and circular capsulotomy.

24.3.3 Summary of Recommendations

Several case reports have documented the utility of FLACS in eyes with zonular weakness. Based on published literature and the authors’ experience, the following are important considerations for using FLACS in zonular weakness:

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  Accurate imaging is the cornerstone to successful FLACS of cataracts with zonular weakness.

  
  
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  It is important to carefully examine the intraoperative image of the lens boundaries prior to activating the laser. Ensure that the anterior and posterior capsules have been correctly identified and delineated by the laser software.

  
  
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  In traumatic subluxation, the status of the posterior capsule needs to be inspected on the intraoperative optical coherence tomography (OCT) to identify any pre-existing breaks. In the latter situation, expansion forces created by the cavitation bubbles formed during lens fragmentation could enlarge a pre-existing posterior capsular dehiscence. Nuclear segmentation and softening are best kept to a minimum in such situations.

  
  
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  To maximize likelihood of centering the capsulotomy on the capsular bag, use the custom capsulotomy or, if available, the scanned capsule setting.

  
  
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  Widen the laser treatment gates while creating the capsulotomy to ensure creation of a capsulotomy in eyes with lens tilt.

  
  
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  Additional recommendations for facilitating FLACS in eyes with zonular weakness are in ▶ Table 24.1.

  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  

  Table 24.1 Guidelines for performing FLACS in subluxed cataracts

  Do not	Do
  Create a large capsulotomy	Instead, customize capsulotomy size to ensure an adequate intraocular lens optic capsular overlap
  Center capsulotomy with reference to the pupil	Customize capsulotomy position to be centered on the decentered capsular bag
  Use excessive energy or extensive lens softening	Set repetition rate and number of segments based on nuclear density
  Be aggressive with anterior vitrectomy	Stabilize the bag as early as is safely possible. If there is no vitreous in the region of capsulotomy, stabilize the bag before doing an anterior vitrectomy
  Anchor bag only in a segment where the zonular weakness is extensive	In eyes with global weakness, use multiple capsular tension segments to stabilize the bag before proceeding with phacoemulsification

24.4 Eyes with Previous Surgeries

Not uncommonly, cataract surgeons encounter eyes that have had prior surgical procedures. Some of these procedures can pose unique challenges during cataract surgery. In this section, we will consider the challenges presented in such situations and the options to mitigate these challenges by performing FLACS instead of manual phacoemulsification.

24.4.1 Eyes That Have Previously Undergone Penetrating Keratoplasty

Surgical Challenges

Cataract surgery in a patient with previous penetrating keratoplasty (PKP) requires careful consideration of a number of issues to ensure both a high quality of cataract surgery and long-term survival of the corneal transplant. Visualization at and peripheral to the graft–host junction can be difficult due to a combination of high regular and irregular astigmatism, the corneal incision scar, and any pre-existing peripheral corneal pathology. These factors can make surgical maneuvers during manual cataract surgery more challenging. One risk in particular is the likelihood of the capsulorhexis tearing out inadvertently due to suboptimal visualization. Endothelial damage due to excessive need for ultrasonic energy (as is frequently required in dense cataracts) can cause or hasten corneal failure. Traditional phacoemulsification may require conservative use of ultrasound and capsular staining among other techniques to mitigate those challenges. The femtosecond laser offers distinct benefits for these patients by allowing real-time imaging to guide capsulotomy placement and by also decreasing the ultrasound time and energy during removal of the fragmented and softened nucleus. ^{13,​ 14}

Reported Evidence

Martin and colleagues reported treating 12 post-PKP patients who underwent FLACS. ⁷ Docking in all cases was successful with the SoftFit patient interface (LenSx laser). They suggested increasing the energy level, if required, in eyes with reduced corneal clarity. For laser delivery, their initial settings were between 10 and 12 µJ with final settings reduced to 6 µJ. Nagy and colleagues reported a 33-year-old man who underwent FLACS after PKP. ⁸ Intraoperative OCT identified the scar at the graft–host junction, and the scar did not interfere with the laser capsulotomy. The corneal incisions were created manually because of the peripheral location of the 7-mm transplant. They reported that no ultrasound was required to remove the lens and that the endothelial cell count remained unchanged up to a year after surgery.

Summary of Recommendations

A summary of recommendations is presented in ▶ Table 24.2.

24.4.2 Eyes That Have Undergone Prior Radial Keratotomy

Eyes that have undergone prior RK have radial corneal scars that can potentially interfere with laser delivery and can create an incomplete capsulotomy (▶ Fig. 24.2a, b). To our knowledge, there are no published reports on this topic. However, in the authors’ experience, the dos and don’ts for such eyes are along the lines of that outlined for eyes with prior PKP. In eyes with four RK incisions, clear corneal incisions (CCI) can be placed. The enface image on intraoperative OCT can be used to position the CCI while ensuring it does not overlap with any of the RK incisions (▶ Fig. 24.2c).

24.4.3 Eyes That Have Had Prior Glaucoma Filtration Surgery

Surgical Challenges

In glaucoma patients who have previously undergone trabeculectomy, the bleb might act as an obstacle to a proper docking process during FLACS. Liquid immersion interfaces offer the opportunity to prevent excessive pressure on the filtration bleb and excessive deformation of the globe. One consideration that is important in glaucoma patients is to not have a significant intraocular pressure (IOP) elevation during docking to avoid the possibility of damage to an already compromised optic nerve head.

Schultz et al investigated changes in IOP during FLACS. They report only a moderate increase in IOP when using a fluid-filled interface for docking to the system. ¹⁵ In a group of 100 eyes using the Catalys laser, a mean increase of only 10.3 mmHg was reported and IOP 1 hour after surgery was not significantly higher than the preoperative values, suggesting that further IOP-related damage in glaucoma patients undergoing FLACS would be unlikely. ¹⁵

Reported Evidence

In our experience, placing the suction ring has been uneventful in eyes with small and moderate filtering blebs. Kinnas and colleagues performed FLACS successfully in an eye with prior glaucoma filtration surgery (▶ Fig. 24.3). The Catalys femtosecond laser system and 16-mm suction rings were used uneventfully in their case, permitting effective imaging and FLACS (Personal communication, Spero Kinnas, MD, Westchester, IL). The filtering bleb remained unchanged over a 10-month follow-up period. Martin and colleagues provided a brief report of their experience performing FLACS with the LenSx femtosecond platform in eight posttrabeculectomy eyes. ⁷ They found no increased difficulty with docking or intrableb hemorrhage after laser treatment. ⁷ In all eyes, bleb morphology, IOP, visual fields, and retinal nerve fiber layer OCT remained stable through 6 months of follow-up (▶ Fig. 24.3).

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