Purpose
To compare the benefit of femtosecond laser-assisted cataract surgery (FLACS) versus phacoemulsification (PE) and 2 fragmentation patterns in managing dense cataracts.
Design
Randomized controlled trial.
Methods
Patients with nuclear opacity (NO) grade >5 (Lens Opacities Classification System III) were enrolled at the Singapore National Eye Centre. Patients who were unsuitable for FLACS, whose corneal endothelial cell count (ECC) was <1,500 cells/mm 2 , or had cataracts with additional complexities were excluded from the study. Eyes were randomized to PE, 600 μm grid (FLACSg), or 16-segment fragmentation (FLACS16) in 2:1:1 ratio. The Victus (Bausch & Lomb) laser platform and in situ phacoemulsification chop technique was used. Data for patient demographics, preoperative, and 1 month postoperative best-corrected visual acuity (BCVA), ECC, effective phacoemulsification time (EPT), and perioperative complications were collected. Outcome measurements were the loss of ECC at 1 month and EPT.
Results
Ninety-three patients were randomized to PE (48), FLACSg (22), and FLACS16 (23). Majority were Chinese (87; 93.5%). Mean age was 74.3 ± 8.8 years of age. Cataracts were mostly graded as NO 5-6 (49; 61.3%). EPT among treatment arms was not different ( P = .097, one-way ANOVA) but was significantly higher for NO >6 than NO <6 ( P < .001, general linear model). ECC loss was significantly less in FLACSg than in PE ( P = .018, Bonferroni correction). Mean 1-month postoperative LogMAR BCVA (0.23 ± 0.20) was significantly better than preoperative BCVA (1.02 ± 0.85; P < .001, paired t test) but not different between PE and FLACS.
Conclusions
FLACSg but not FLACS16 significantly lowered the mean ECC loss during phacoemulsification in dense cataracts.
Handling dense cataracts can present technical challenges. The absence of a red reflex makes visualization of a thin capsule difficult, and capsulorhexis, which is often made a little larger than 5 mm to facilitate removal of chunky nuclear pieces, may run out. Although Trypan blue dye significantly helps capsule visualization in a white cataract, but the contrast obtained in a dense cataract is moderate against a dark background. Capsular fibrosis may be encountered in these advanced cataracts, which makes tearing across them hazardous as this may result in a capsulorhexis run out.
Most surgeons today use a “stop-and-chop” technique in which a trough is initially sculpted, and the nucleus is split in half. The halves are then chopped into smaller pieces and emulsified. In these brown cataracts, sculpting an adequate trough requires high levels of ultrasound energy and multiple passes as the cataract is not only hard but also thick and leathery. Inadequate ultrasound energy may result in pushing on the nucleus and disrupting the zonular support. Separating the nuclear fragments can be a difficult task due to the tenacious fibers, especially at the posterior plate. Wound burns can easily develop if the incision is too tight or the ultrasound energy is too high and/or exposed for too long. In addition, these advanced cataracts are associated with other challenges such as corneal guttata, capsular fibrosis, zonular weakness, shallow anterior chambers, and thin floppy posterior capsules. In order to efficiently manage dense cataracts, an in situ “chop” technique is recommended. However, this technique is more difficult to master.
Femtosecond laser-assisted cataract surgery (FLACS) allows the surgeon to create a capsulotomy of desired size and centration within seconds. The laser is able to transect bands of capsular fibrosis, which can cause the capsulorhexis to go astray. Next, the nucleus can be fragmented according to different patterns. This enables the surgeon to readily separate the nuclear pieces still bound together at the lens equator and posteriorly in the depth of the lens. Fragmenting the nucleus into small pieces softens the dense nucleus, facilitating nuclear segmentation and minimizing the effective phacoemulsification time (EPT), sparing the cornea. In a meta-analysis of 14,567 eyes, comparing efficacy and safety of FLACS with manual phacoemulsification (PE), the former resulted in reduced EPT, central corneal thickness, and loss of endothelial cell count. , Dick and associates showed that gridding the nucleus into smaller fragments resulted in a reduction of ultrasound energy, and when the fragment size was 350 μm, aspiration without ultrasound was possible. However, the effect of radial segmentation into smaller pieces has not been investigated. This study sought to compare the effect of FLACS versus PE and the efficacy of grid (FLACSg) versus 16-segment (FLACS16) fragmentation pattern in managing dense cataracts.
Methods
This is a prospective randomized controlled study conducted at the Singapore National Eye Centre from September 1, 2016, to January 31, 2018. Cataracts with nuclear density Lens Opacities Classification System III (LOCS III) nuclear opacity (NO) grade 5 or more without additional abnormalities that would complicate the cataract surgery were recruited. Eyes were grouped into NO5 and NO6 cases, and the second group which included eyes with NO grade greater than 6. Those eyes were randomized to 1 of 3 treatment arms: 1) PE; 2) Femtosecond laser fragmentation of the nucleus using a grid pattern of 600 μm (FLACSg); or 3) femtosecond laser fragmentation of the nucleus into 16 segments using a pie pattern (FLACS16) in a ratio of 2:1:1. Randomization was done by following a set of computer-generated list of random numbers administered by the study coordinator. All surgeries were performed by a single experienced surgeon (S.P.C.). This study was approved by the SingHealth Centralized Institutional Review Board (CRB reference number 2015/2292) and the research adhered to the tenets of the Declaration of Helsinki. This study received funding from the Singapore National Eye Centre-Singapore Eye Research Institute Health Endowment Fund.
Preoperatively, the best-corrected visual acuity (BCVA), corneal status, anterior lens capsule condition, NO grade, dilated pupil size, macular status, peripheral retina, cup:disc ratio, and intraocular pressure were documented. In addition, the anterior chamber depth and lens thickness from the biometric data were recorded, and the endothelial cell count and optical coherence tomography of the optic nerve and macular were checked for pre-existing pathology. Slit-lamp photography was performed for all cataracts after pupil dilation for documentation of the nuclear density grade and classified according to the LOCSIII classification. Ultrasonography biomicroscopy was done to rule out zonular dehiscence.
Exclusion criteria were an endothelial cell count of 1,500 cells/mm 2 ; eyes unsuitable for FLACS, such as tight sunken palpebral apertures; and uncooperative patients and cataracts with additional complexities, for example, white cataracts, zonulysis, small pupils (<6 mm diameter); advanced glaucoma; and capsule fibrosis.
For eyes randomized to FLACS, the Victus (Bausch + Lomb, Munich, Germany) laser platform was used to initially create a 5.0-mm pupil centered, round capsulotomy. Those randomized to FLACSg then underwent nuclear fragmentation using a grid pattern of 600 μm. No segments were added, and the extent of the grid pattern was limited by the pupil size. Eyes assigned to FLACS16 underwent nuclear fragmentation into 16 pieces, using a pie pattern. The extent of fragmentation was maximized to the pupil, leaving a safety margin of 500 μm all around. In addition, the anterior capsule offset was 600 μm, and the posterior capsule offset was 700 μm. The femtosecond laser energy for both capsulotomy and nucleus fragmentation was set to the maximum setting in all cases: 7.0 μJ for capsulotomy and 9.0 μJ for nucleus fragmentation. For the capsulotomy, the horizontal spot spacing was 6 μm and the vertical was 4 μm. For nuclear fragmentation, both the horizontal and vertical spot spacing were set at 10 μm for 16 segments and 14 μm for grid pattern.
A 2.65-mm temporal clear cornea incision was created. The eye was filled with dispersive ophthalmic viscoelastic (OVD) material (Viscoat; Alcon Laboratories, Fort Worth, Texas, USA). After the disc of anterior capsule was removed, minimal hydrodissection was performed. The in situ chop technique using the Stellaris PC (Bausch + Lomb, Rochester, New York, USA) for PE was performed in all cases regardless of the technique category randomized to. A small vertical trench was initially created until the core of the nucleus was reached. The nucleus was impaled with high ultrasound energy and vacuum settings. A chopper (Nagahara chopper, ASICO, Westmont, Illinois, USA) was used for horizontally chopping in the manual cases, and for the FLACS cases, it was used for lateral separation of the prefragmented nuclear pieces, until the posterior plate was also separated. The nuclear pieces were emulsified and removed as they were dissected from the rest of the nucleus. Irrigation and aspiration of the cortex was done, followed by implantation of a single piece a hydrophobic acrylic IOL (product number SA60AT; Alcon Laboratories). The OVD was aspirated, and the corneal incisions were sealed. Topical levofloxacin 0.5% and prednisolone acetate 1% were started initially at 3 hours and reduced to 4 times daily at 1 week. Eye drops were stopped between 4 to 6 weeks postoperatively.
These patients were reviewed at 1 day, 1 week (between 5 to 7 days), and 1 month (4-6 weeks) postsurgery. We collected the following data: preoperative and 1 month postoperative BCVA and endothelial cell count preoperative and at 1 month postoperatively, the effective EPT, surgical time in minutes. and perioperative complications.
Sample size calculation for this prospective randomized study was calculated based on a previous small pilot study comparing femtosecond and nonfemotosecond eyes. From the previous study, the required sample size was 25 for each group, based on the assumption of a type I error (α) of 0.05 and power (1-B) of 0.8 to detect a 10% difference between the treatments. The sample size was increased to approximately 50 cases in each group for further analysis between the femtosecond groups.
The outcome measurements were EPT and loss of endothelial cell count (ECC), the latter of which was calculated by the differences between the pre- and postoperative ECC. One-way ANOVA was used for comparing EPT among the 3 groups and the 2-way ANOVA (general linear model) for interaction between EPT and density of cataract. The square root transformation of EPT was taken to fit the normal distribution when using ANOVA and regression analysis test. Bonferroni correction of ANOVA test was used for multiple comparison method. All analyses were computed using SPSS version 25 software (SPSS, Chicago, Illinois, USA).
Results
Ninety-four patients were enrolled into the study. One patient withdrew before randomization, and the remaining 93 were randomized: 48 (51.6%) to phacoemulsification; 22 (23.7%) to FLACSg; and 23 (24.7%) to FLACS16. The majority were Chinese (87 subjects; 93.5%). The patients’ mean age was 74.3 ± 8.8 years. A majority of the cataracts were NO grades 5-6 (55 subjects; 59.1%). Preoperative parameters among the 3 treatment groups are compared in Table 1 . There were no significant differences found. All surgeries were uneventful, and there were no intraoperative complications. In particular, there were no capsulotomy run-outs or posterior capsule ruptures.
| Preoperative Parameters | PE (n = 48) a | FLACS 16 (n = 23) b | FLACSg (n = 22) c | P | Statistical Test |
|---|---|---|---|---|---|
| Mean ± SD age, y | 75.8 ± 8.0 | 72.0 ± 9.0 | 73.5 ± 9.9 | .199 | One-way ANOVA d |
| Males | 27 | 12 | 12 | .949 | Pearson χ 2 |
| Females | 21 | 11 | 10 | ||
| Chinese | 46 | 21 | 20 | .650 | Pearson χ 2 |
| Non-Chinese | 2 | 2 | 2 | ||
| Density of cataract | |||||
| Nuclear opacity ≤6 | 29 | 12 | 14 | .712 | Pearson χ 2 |
| Nuclear opacity >6 | 19 | 11 | 8 | ||
| Mean ± SD ACD (mm) | 3.02 ± 0.39 | 2.97 ± 0.38 | 3.13 ± 0.40 | .406 | One-way ANOVA |
| Mean ± SD lens thickness | 4.79 ± 0.36 | 4.74 ± 0.45 | 4.71 ± 0.40 | .785 | One-way ANOVA |
| Mean ± SD preoperative best corrected visual acuity (LogMAR) | 1.08 ± 0.82 | 0.90 ± 0.83 | 1.03 ± 0.98 | .703 | One-way ANOVA |
| Mean ± SD preoperative endothelial cell count (cell/mm 2 ) | 2,551 ± 354 | 2,464 ± 536 | 2,652 ± 274 | .278 | One-way ANOVA |
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