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Clinical science
Visual and refractive outcomes and complications in femtosecond laser-assisted versus conventional phacoemulsification cataract surgery: findings from a randomised, controlled clinical trial
  1. Daliya Dzhaber1,
  2. Osama M Mustafa1,
  3. Fares Alsaleh2,
  4. Yassine J Daoud1
  1. 1Cornea, Cataract and External Diseases, Johns Hopkins Wilmer Eye Institute, Baltimore, Maryland, USA
  2. 2Ophthalmology Department, McGill University Health Centre, Montreal, Quebec, Canada
  1. Correspondence to Dr Yassine J Daoud, Wilmer Eye institute, Johns Hopkins University, Baltimore, MD 21287, USA; ydaoud1{at}jhmi.edu

Abstract

Background/aim To compare visual and refractive outcomes, changes in intraocular pressure (IOP), and complications of femtosecond laser-assisted cataract surgery (FLACS) to conventional phacoemulsification surgery (CPS) in paired eyes from the same patients.

Methods This is a secondary analysis of an intraindividual, randomised, controlled clinical trial including 110 paired eyes from 55 patients that were randomised into either FLACS or CPS groups. Outcomes were recorded at baseline and postoperatively during a 3-month follow-up period.

Results Uncorrected distance visual acuity and corrected distance visual acuity were similar between FLACS and CPS over the follow-up period (p>0.05). The mean absolute refractive error was not significantly different between the two groups at postoperative month 1 (POM1) (0.3±0.2 D in FLACS vs 0.4±0.3 D in CPS, p=0.18) and month 3 (POM3) (0.3±0.3 D in FLACS vs 0.3±0.3 D in CPS, p=0.71). IOP was statistically higher in the FLACS group on postoperative day 1 (20.6±5.7 mm Hg for FLACS and 18.0±4.9 mm Hg for CPS, p=0.01). However, it was similar between the two groups subsequently (p>0.05). Intraoperatively, one case of posterior capsular block syndrome was observed in the FLACS group. Postoperatively, one case of newly developed glaucoma was observed in the FLACS group and one case of retinal tears in the CPS group.

Conclusion The 3-month postoperative refractive and visual outcomes were comparable between FLACS and CPS in paired eyes from the same patients. Complication rate was low in the study population.

  • clinical trial
  • intraocular pressure
  • vision
  • lens and zonules

https://doi.org/10.1136/bjophthalmol-2019-314548

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    Introduction

    Cataract extraction with intraocular lens (IOL) implantation remains the mainstay technique for cataract treatment. Technological advancements have led to increased expectations of cataract surgery outcomes, with the emphasis on improving its safety as well as refractive and visual outcomes. Currently, the leading cataract procedure performed in the Western world is conventional phacoemulsification surgery (CPS),1 whose key steps (ie, corneal incisions, capsulorhexis and lens fragmentation) are performed manually. More recently, femtosecond laser (FL) technology has been used to assist in performing these steps.2 The reported benefits of femtosecond laser-assisted cataract surgery (FLACS) include improved centration and precision of capsulotomy and reduced ultrasound power used during phacoemulsification.2–6 More consistent capsulotomies and better intraocular lens centration in eyes after FLACS could hypothetically lead to better refractive outcomes of cataract surgery.

    Because of such perceived advantages of FLACS, there has been a growing interest in exploring outcome-oriented differences between FLACS and CPS. A few reports suggested better uncorrected distance visual acuity (UDVA) with FLACS.7 8 However, others found no significant difference in visual outcomes.9–12 The latter findings were also suggested by a recent large retrospective study.13 We conducted this study to compare visual, refractive and intraocular pressure (IOP) findings between FLACS and CPS during 3 months of postoperative follow-up. We also report on the intraoperative and postoperative complications encountered in both procedures.14 15

    Materials and methods

    This analysis included patients from a randomised controlled clinical trial whereby one eye was randomly assigned into either FLACS or CPS while the fellow eye received the alternative procedure.16 Assignments were made using an online random number generator and were concealed from the operating surgeon (YJD) until the day prior to the surgery for each case. For the purposes of this analysis, the following inclusion criteria were used: Age ≥18 years, presence of bilateral visually-significant cataract, absence of any other ocular pathology or previous/concurrent ocular surgery and availability for 3 months postoperatively at minimum. In total, 77 patients (154 eyes) were eligible for inclusion during the enrolment period. However, 22 patients were later excluded due to missing their 3-month follow-up (6 patients), having the same procedure in both eyes (4 patients) or requesting a speciality IOL (12 patients). Therefore, 110 eyes of 55 patients were evaluated in this study.

    The primary outcomes examined in this study included postoperative UDVA, corrected distance visual acuity (CDVA), manifest refraction (MRx) and mean absolute refractive error. Secondary outcomes targeted IOP changes as well as intraoperative and postoperative complications. The clinical trial was conducted in accordance with Health Insurance Portability and Accountability Act (HIPAA) regulations. Patients provided written informed consent to participate in the study.

    All patients had a complete preoperative examination including slit-lamp biomicroscopy, applanation tonometry, ophthalmoscopy through dilated pupils, UDVA, CDVA, MRx and brightness acuity test (BAT). IOL power calculations and predicted refraction as well as keratometry, anterior chamber depth and axial length were obtained by means of a non-contact partial coherence laser interferometry (IOLMaster, Carl Zeiss Meditec AG, Jena, Germany). In both groups, a monofocal aspheric IOL was implanted. The IOL power was calculated using the Holladay 2 formula.

    Details of the surgical procedure for FLACS and CPS groups are provided elsewhere.16 In brief, the FLACS group underwent laser pretreatment by which a 5.5 mm capsulotomy and lens fragmentation were initially performed, followed by creation of a two-plane 2.8 mm main corneal wound and a one-plane 1.2 mm side-port incision. All FL procedures were performed using the same laser platform (LenSx laser, Alcon Laboratories, Inc, Fort Worth, Texas, USA). The CPS group underwent manual one-plane 1.2 mm paracentesis and two-plane 2.8 mm main corneal incision, followed by a manual, continuous curvilinear capsulorhexis with an intended diameter of 5.5 mm. Subsequently, both groups underwent phacoemulsification (Infiniti Vision System, Alcon Laboratories, Inc, Fort Worth, Texas, USA) with a pop-and-chop technique for lens fragmentation. After complete cataract extraction, IOL implantation was performed, and stromal hydration was applied to close corneal incisions at the end of the procedure.

    All study participants were monitored intraoperatively for complications. The presence of incomplete capsulotomy, anterior capsular tags, anterior radial capsular tears and posterior capsular rupture was recorded.

    A combination steroid-antibiotic ointment was placed on the eye at the end of the procedure, and the eye was covered with a patch. Patients were instructed to an antibiotic (four times a day for 1 week), steroids and non-steroidal anti-inflammatory drops (four times a day during the first week gradually tapered over the next 3 weeks).

    UDVA and IOP were measured at POD1 (postoperative day 1), POW1 (postoperative week 1), POM1 (postoperative month 1) and POM3. CDVA, MRx and the mean absolute refractive error were obtained at POM1 and POM3. Complications were recorded postoperatively at each follow-up visit and included: corneal oedema, IOP spike (defined as IOP ≥30 mm Hg on POD1), ocular inflammation, cystoid macular oedema (CME), epiretinal membrane formation and retinal detachment (RD).

    The outcomes were compared between the two techniques using Paired t and Wilcoxon signed-ranks tests, where appropriate. Visual acuity was transformed to logarithm of the minimum angle of resolution (logMAR) equivalents to facilitate the statistical analysis.17 18 McNemar’s test was used to compare proportion of cases achieving visual and refractive outcomes around standard cut-offs between the two groups. Eyes aimed for near were excluded from the analysis of postoperative UDVA, MRx and spherical equivalent. The sample size was chosen to achieve a statistical power of 80% for the group comparison at a 5% significance level. All analyses were conducted using Stata V.14.0/IC (StataCorp LP, College Station, Texas, USA). A p value <0.05 was considered statistically significant.

    Results

    A total of 110 eyes (55 patients) were analysed in this study. The mean age of the patients was 68±9.6 years (range, 33 to 85 years). Over half (58.1%) of the study population were males. There was no significant difference in ocular biometry findings, visual acuity, refraction, BAT and IOP between the FLACS and CPS groups preoperatively (table 1).

    View this table:
    Table 1

    Baseline demographics (mean±SD)

    UDVA and CDVA logMAR scores were not significantly different between the two groups over the follow-up period (table 2). At POM1, UDVA of 20/40 or better Snellen (≤0.3 logMAR) was observed in 75.6% and 76.6% of eyes, in the FLACS and CPS groups, respectively (p=1.0). At POM3, 83.3% and 90.0% of eyes in the FLACS and CPS groups, respectively, achieved UDVA of 20/40 or better (p=0.16). UDVA of 20/20 or better was observed at POM1 in the same percentage of eyes (41.5%, p=1.0) in both groups. At POM3, 56.6% and 63.3% eyes in the FLACS and CPS groups, respectively, had UDVA of 20/20 or better (p=0.48). CDVA of 20/40 or better was observed at POM1 in 95.5% and 97.7% of eyes in the FLACS and CPS groups, respectively (p=0.32). At POM3, 97.2% and 100.0% of eyes in the FLACS and CPS groups, respectively, achieved CDVA of 20/40 or better (p=0.32). At POM1, CDVA of 20/20 or better was observed in 79.5% and 86.4% eyes in the FLACS and CPS groups (p=0.26). At POM3, 86.1% of eyes in the FLACS group and 88.9% of eyes in the CPS group achieved a CDVA of 20/20 or better (p=0.56).

    View this table:
    Table 2

    Postoperative visual outcomes logMAR (mean±SD)

    Postoperatively, no statistically significant difference was observed in manifest refraction parameters over the follow-up period (table 3). In addition, the mean absolute refractive error was not significantly different between the two groups at POM1 (0.3±0.2 D in FLACS vs 0.4±0.3 D in CPS, p=0.18) and at POM3 (0.3±0.3 D in FLACS vs 0.3±0.3 D in CPS, p=0.71). At POM1, 82.5% and 70% of eyes in the FLACS and CPS groups, respectively, were within ±0.5 D of the target refraction (p=0.17). At POM3, 83.8% and 81.1% of eyes in the FLACS and CPS groups achieved a mean absolute refractive error within ±0.5 D (p=0.76). Target refraction within ±1 D at POM1 was achieved in 100% eyes in the FLACS group vs in 97.5% in the CPS group (p=0.32). At POM3, 94.6% and 97.3% in the FLACS and CPS groups, respectively, were within ±1 D of target refraction (p=0.56).

    View this table:
    Table 3

    Postoperative refractive findings: sphere, cylinder and spherical equivalent (D) for patients aimed for emmetropia (mean±SD)

    A significantly higher IOP was observed in the FLACS group on POD1, with a difference of 2 mm Hg, on average, between the two groups (p=0.01). An IOP spike was observed in five eyes in the FLACS group and in one eye in the CPS group. However, the mean IOP was not significantly different between the two groups after the first postoperative day (table 4).

    View this table:
    Table 4

    Postoperative intraocular pressure measurements (mm Hg; mean±SD)

    Intraoperatively, one case of posterior capsular block syndrome (PCBS) was observed in the FLACS group, resulting in a posterior capsular rupture, anterior vitrectomy and implantation of the IOL in the sulcus. There were no cases with incomplete capsulotomy, anterior capsular tags, or anterior radial capsular tears observed in the study.

    Postoperatively, glaucoma developed in one eye 2 months after surgery in the FLACS group. In the CPS group, one eye with four retinal tears was observed at POM3. No eyes developed postoperative CME, RD or endophthalmitis. No eyes were blinded in the study.

    Discussion

    In this study, we compared differences in postoperative refractive findings, visual outcomes, IOP and complications between paired eyes undergoing either FLACS or CPS. Our results did not show statistically significant difference in postoperative UDVA and CDVA between the two techniques over the follow-up period. Also, there was no significant difference found in the percentage of eyes targeted for distance who achieved UDVA of 20/40 or better and 20/20 or better at POM1 and POM3. The same results were found for CDVA. These findings are consistent with the majority of published studies that have not found significant postoperative benefit of FLACS over CPS.9–14 In a previous intraindividual clinical trial, a statistically significant difference in UDVA was only found between the two groups at POW1.7 After that, no statistically significant difference was detected between the two techniques.7 These findings were confirmed by a recent meta-analytical examination of the published literature, which found no significant difference in mean absolute refractive errors as well as visual outcomes between the two techniques.9 Likewise, a more recent, large retrospective study did not find statistically significant difference between eyes undergoing FLACS or CPS with respect to visual outcomes.13 The percentages of eyes targeted for distance that achieved UDVA of 20/20, 20/25 and 20/30 were also found to be similar between the two groups.13

    In our study, we were unable to detect statistically significant refractive advantage of FLACS over CPS postoperatively. Although the percentage of eyes with mean absolute refractive error ≤0.5 D was higher in the FLACS group at POM1 and POM3, the difference was not statistically significant. Also, the proportion of eyes with mean absolute refractive error ≤1 D were not significantly different despite the higher percentage in the FLACS group at POM1 and in the CPS group at POM3. The hypothetical refractive advantage of FLACS is thought to be its creation of a more precisely centred, circular and reproducible anterior capsulotomy, leading to a more predictable effective lens position and a better IOL optic centration postoperatively compared with CPS.5 7 19 20 However, recent data showed a lack of correlation between capsulorhexis centration and circularity and postoperative refraction at 1 year.21 Nonetheless, better refractive parameters were occasionally encountered in either of FLACS or CPS. Filkorn et al found a statistically significant difference in mean absolute refractive error 6 weeks after surgery, favouring FLACS over CPS.22 This is in contrast with a study performed by Ewe et al, where CPS outperformed FLACS becoming progressively greater as the window of allowable mean absolute refractive error narrowed from within 2.0 D, to 1.5 D, to 1.0 D, to 0.5 D of preoperative target.23 According to the aforementioned intraindividual clinical trial, FLACS offers earlier refractive stabilisation compared with CPS (at POW1 for FLACS and POM1 for CPS).7 Despite the few sporadic findings of significant differences between FLACS and CPS in terms of visual24 and refractive outcomes,22 25 the majority of the current body of evidence supports the similar outcomes between the two procedures,9–13 19 21 26 which is in line with the findings in our study. Since the patient population eligible for this study was stringently selected to include eyes that are otherwise healthy (with no comorbid eye conditions), no major changes in visual acuity or refraction was expected to occur after the third postoperative month.27–29

    IOP spike was observed in five eyes in the FLACS group and in one eye in the CPS group. On average, IOP measurements were significantly higher in FLACS group on POD1 (p=0.01). This is in line with the previous observations of higher rates of elevated IOP in the FLACS group than in CPS.8 14 Data from earlier reports suggested that an increase in IOP immediately after the laser pretreatment may be due to high pressure applied to the eye during suction of the FL interface.30 However, because FL protocols have changed (with a significant decrease in that pressure to 16 mm Hg) since the time some of the earlier reports were published, we suspect that the ‘high-pressure-application’ factor cannot explain the increase in IOP that we observed on POD1, and that other factors may be involved. For example, the higher level of prostaglandins found in eyes after FLACS compared with CPS might potentially explain that.26 Regardless of the underlying mechanism, it should be noted that the difference in mean IOP between the two groups was 2 mm Hg at POD1, which—despite the statistical significance—is unlikely to be of concern clinically. Further, the IOP normalised soon afterwards in both groups.

    In our study, one eye developed postoperative glaucoma in the FLACS group, necessitating trabeculectomy 2 months after cataract surgery. To date, data on the persistence of postoperative IOP changes after FLACS in comparison with CPS are not sufficient in the literature. Further investigations are required for a better understanding of the FL’s effect on IOP changes and glaucoma formation in such eyes.

    We also encountered a case of PCBS, one of the most feared FLACS complications. This complication is related to cavitation from gas bubbles formed during lens fragmentation. When bubbles remain trapped within or behind the nucleus, PCBS develops with subsequent posterior capsular rupture. It was first reported in 2011.31 A delay of the hydrodissection step until the nucleus is bisected has been recently suggested to allow the release of the preformed gas bubbles into the anterior chamber and elimination of the risk of the PCBS and capsular rupture in FLACS eyes.32

    One eye with four horseshoe retinal tears with no subretinal fluid was observed in the CPS group at POM3. Preoperatively, no identifiable risk factor was found in that eye and no peripheral retinal degenerations were noticed on dilated fundus exam. As a prophylaxis of retinal detachment, laser retinopexy was performed in that eye.

    To conclude, in paired eyes from the same patients managed with either FLACS or CPS, the 3-month postoperative refractive and visual outcomes were similar between the two procedures. IOP was also comparable between the two groups after POD1. Further investigations of the effect of the FL on postoperative IOP changes and development of other complications is recommended.

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    Footnotes

    • DD and OMM contributed equally.

    • ——————

    • DD and OMM are joint first authors.

    • Contributors Research design: YJD; data acquisition and/or research execution: DD, FA; data analysis and/or interpretation: DD, OMM, YJD; manuscript preparation: DD, OMM, YJD; manuscript revision: DD, OMM, YJD.

    • Funding Unrestricted research grants from the Michael O’Bannon Foundation and the Turner family. Wilmer Eye Institute pooled professor fund.

    • Competing interests None declared.

    • Patient consent for publication Obtained.

    • Ethics approval Institutional review board at the Johns Hopkins University.

    • Provenance and peer review Not commissioned; externally peer reviewed.

    • Data availability statement All data relevant to the study are included in the article or uploaded as supplementary information. Data are available upon reasonable request from the corresponding author.