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ORIGINAL ARTICLE
Year : 2015  |  Volume : 22  |  Issue : 3  |  Page : 356-361  

Determinants of visual outcomes in femtosecond laser assisted cataract surgery and phacoemulsification: A nested case control study


1 Department of Research, King Khaled Eye Specialist Hospital, Riyadh, Saudi Arabia
2 Department of Anterior Segment, King Khaled Eye Specialist Hospital, Riyadh, Saudi Arabia; Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA

Date of Web Publication1-Jul-2015

Correspondence Address:
Rajiv Khandekar
Department of Research, King Khaled Eye Specialist Hospital, Riyadh, Saudi Arabia

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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0974-9233.159762

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   Abstract 

Purpose: We present the visual outcomes 6 weeks following Femtosecond laser assisted cataract surgery (FLACS) and conventional phacoemulsification cataract extraction (CE) cataract surgeries in 2013.
Materials and Methods: This was a review of health record type of study. Eyes operated by FLACS and an equal number of conventional phacoemulsification (CE) on the same day by same surgeon were included in the study. Demographics, preoperative status, operative details and the best-corrected visual acuity (BCVA) at 6-8 weeks following surgery were noted. BCVA of >20/60 was considered as "excellent." The rate and determinants of "excellent" vision were calculated.
Result: Study population comprised of 154 eyes. Both FLACS and CL groups had 77 eyes. Visual acuity at 6-8 weeks was "excellent" in 44 (60%) eyes of FLACS group and 36 (40%) eyes of CE. Visual outcome following FLACS and conventional surgery was not different (Odd's ratio [OR] 1.5 [95% confidence intervals [CI]: 0.8-2.9]). Operating surgeon did not significantly influence the visual outcomes following FLACS (OR = 1.6) and CE (OR = 0.4). Association of the grade of lens opacities to the visual outcome was not affected by type of surgery (χ2 = 0.5, P = 0.2). The duration of surgery in CE and FLACS groups was not significantly different (−3.2 min [95% CI: −13; 6.6]).
Conclusion: Visual outcomes at 6-8 weeks following CE were not different from FLACS. Visual outcomes following FLACS and CE were not influenced by the operating surgeon or severity of the cataract. The time required for FLACS was greater than that required for CE.

Keywords: Cataract, Femtosecond laser assisted cataract surgery, Lens, Vision


How to cite this article:
Khandekar R, Behrens A, Al. Towerki AE, May W, Motowa S, Tailor K, Souru C. Determinants of visual outcomes in femtosecond laser assisted cataract surgery and phacoemulsification: A nested case control study. Middle East Afr J Ophthalmol 2015;22:356-61

How to cite this URL:
Khandekar R, Behrens A, Al. Towerki AE, May W, Motowa S, Tailor K, Souru C. Determinants of visual outcomes in femtosecond laser assisted cataract surgery and phacoemulsification: A nested case control study. Middle East Afr J Ophthalmol [serial online] 2015 [cited 2022 May 18];22:356-61. Available from: http://www.meajo.org/text.asp?2015/22/3/356/159762


   Introduction Top


Cataract surgery is the most common ophthalmic surgery at most ophthalmology departments. The World Health Organization (WHO) recommends both qualitative and quantitative assessments of the outcomes of cataract surgery as part of an audit for any institution, region or country. [1] The WHO and the International Agency for the Prevention of Blindness have set a benchmark of 20/20 uncorrected distance visual acuity at 6-8 weeks postoperatively in at least 90% of patients undergoing cataract surgery with intraocular lens (IOL) implantation. [2] Based on periodic surgical audits, an institution can determine if it meets this benchmark, identify the reasons for shortfalls and address the shortcomings. [3],[4]

Femtosecond laser-assisted cataract surgery (FLACS) has been recently introduced into surgical practice. It was initially introduced at the King Khaled Eye Specialist hospital (KKESH) for managing cataract cases in December 2012. [5] The advantage of FLACS is the mitigation of the risks of manual capsulorhexis, decreases phacoemulsification time, decreases IOL manipulation, lens tilt and de-centration. [6],[7],[8],[9],[10] As with any new technology, there is a surgical learning curve for FLACS that could compromise outcomes. [11] A review of the safety and efficacy of FLACS suggested that visual outcomes, complication rates and cost-effectiveness of FLACS should be compared to conventional phacoemulsification cataract surgery. [12]

This study was performed at KKESH to evaluate the determinants of visual outcomes in FLACS and conventional phacoemulsification cataract surgeries in 2013.


   Materials and Methods Top


The Institutional Research Board at KKESH approved this study. All eyes that underwent FLACS between January and July 2013 and an equal number of eyes that underwent conventional phacoemulsification cataract extraction (CE) on the same day were included in this study. A surgical audit was performed on all cases.

We assumed that 65% of eyes in FLACS and 40% of eyes in CE group will have excellent grade of vision. To achieve 95% confidence intervals (CI) and 80% power in this unmatched nested case-control study with 1:1 ratio, at least 70 cases in both groups.

The FLACS commenced in our institution in November 2012. Around 20 cases operated in the first 2 months of commissioning new equipment, were excluded from our study. If cataract surgery was combined with surgery to manage other comorbidities like retinal disease, glaucoma or corneal pathologies, etc., such cases were excluded from our study. All cases operated using FLACS while study period were sequentially included in this study. Similar number of phaco surgeries (CE) carried out on the same day by the same surgeon, but without FLACS were also included in the study.

At the time of this study, FLACS was performed using the Victus femtosecond laser (Bausch and Lomb Inc., Rochester, NY, USA). The patient was supine at the femtolaser, and topical anesthetic was instilled in the eyes. The docking mechanism was attached to the cornea; the laser was brought into the docking mechanism, and suction was applied. With the patient properly aligned at the femtosecond laser, optical coherence tomography of the anterior segment was first performed followed by a circular capsulorrhexis with the femtosecond laser. The capsulorhexis was generally 5-6 mm in diameter. However, it varied according to the size of dilated pupil. Then nucleus fragmentation was performed as four radial lines and two circles <3 mm diameter. The Victus laser does not perform corneal incisions.

Subsequently conventional phacoemulsification surgery was performed. The patient was prepared in a sterile fashion and draped using povidone iodine and an occlusive drape. Corneal incisions were performed with a 2.4 mm keratome for the primary incision. Aside port incision was made. The central capsule was carefully removed. Hydrodissection was performed with caution in FLACS patients to avoid capsular block syndrome. In the conventional surgery group, the capsulorrhexis, nuclear division and corneal incisions were performed manually. The remainder of the surgery was performed in the standard fashion.

Surgery start time was defined as the time that the patient arrived in the operating room. The end of surgery was defined as the time that the patient was moved out of the operating room.

Routine preoperative parameters were visual acuity, intraocular pressure, anterior segment and fundus examination. Preoperative and postoperative visual acuity was evaluated as presenting and the best-corrected visual acuity (BCVA). Complications during surgery such as capsular rupture, lens dislocation and wound leak were noted. Corneal edema, lens dislocation, wound leak, endophthalmitis and retinal detachment were among the complications noted at 24 h following surgery.

The surgeons were particularly vigilant for capsular rupture at the beginning of the case caused by expanding gas bubbles from lens division. They also observed eyes carefully for signs of capsular block syndrome. This would have occurred during hydrodissection due to the expanded size of the nucleus from gas bubbles formed during lens division. This larger nucleus would not allow escape of irrigated fluid, causing the building up of pressure at the posterior capsule resulting capsular rupture. Ruptures identified at entrance to the anterior chamber or immediately after hydrodissection were defined as complications of the femtolaser treatment.

Demographic data included gender and age of the patient. Clinical information included eye operated, ocular comorbidity, type of cataract, systemic comorbidity and intraocular pressure (IOP). Intraoperative data were collected on anterior capsular tear, difficulties in nuclear fragmentation, posterior capsular tear, zonular rupture, etc.

Postoperative data collected within the 1 st postoperative week included wound leak, corneal edema, IOP, anterior chamber reaction, centration of the IOL, status of the anterior capsulotomy, pigment dispersion, posterior capsule status; other complications or morbidity. The identity of surgeon and patient were removed during for data collection from patient charts.

Postoperative information at 6-8 weeks postoperatively included presenting visual acuity and the BCVA, corneal status, anterior chamber reaction, IOL centration, complications if any and the cause of ventriculo-atrial of <20/40 in the operated eye.

The data was entered into an Excel spreadsheet (Microsoft Corp., Redmond, WA, USA). It was converted into a spreadsheet for Statistical Package for Social Studies (SPSS 22) (IBM Corp., New York, NY, USA). The cases and controls were associated to the exposures using univariate analysis. For qualitative variables such as gender, comorbidity, type of cataract, we calculated the odd's ratio (OR) and the 95% CI. For quantitative variables including age and effective surgery time, we 1 st plotted the histogram to evaluate the distribution. If the distribution was normal, we calculated the difference of mean and the 95% CI. If the distribution was normal but skewed, we calculated the log values and evaluated the distribution. If the normality was achieved, we followed the procedure outlined above. If the distribution was not normal, we used a nonparametric method for statistical validation.


   Results Top


There were 154 eyes that underwent either FLACS (n = 77) or CE (n = 77). Characteristics of both groups are compared in [Table 1]. The mean age of participants in FLACS group was 62.2 ± 9.6 years while in CE group it was 61.5 ± 12 years. (difference of mean 0.7 years [95% CI: −3.3-4.7]). The rates of diabetes in both groups was not different (Risk ratio 1.3 [95% CI: 0.9-1.95]).
Table 1: Profile of eyes operated by femtosecond assisted laser (FLACS) and conventional phacoemulsification cataract (EC) surgeries

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The BCVA at 6-8 weeks following both types of cataract surgery was compared. Visual acuity between 20/20 and 20/40 was in 44 (60%) eyes of FLACS group and 36 (40%) eyes of CE. Visual outcome following FLACS and CE surgeries was not different (OR 1.5 [95% CI: 0.8-2.9]).

The association of excellent grade of vision to the group FLACS and CE was not influenced by the type of cataract (Chi-square = 0.5, P = 0.2) [Table 2].
Table 2: Type of cataract in femtosecond assisted laser (FLACS) and conventional phacoemulsification cataract (EC) surgeries

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The mean duration of surgery in the FLACS group was (50.4 ± 29.9 min). The mean duration of surgery in the CE group was (53.6 ± 31.3 min) (mean difference was −3.25 min [95% CI: −13-6.6]).

Following FLACS, one case had zonule rupture, one case had posterior capsular tear and one case had an anterior capsular tear. In CE group, one case had partial descemets membrane striping.

The influence of different parameters on the association of excellent grade of visual outcome and FLACS/CE was studied using binominal regression analysis [Table 3].
Table 3: Factors affecting the visual outcome of >20/60 at 6-8 weeks following femtosecond assisted laser (FLACS) and conventional phacoemulsification cataract (EC) surgeries

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   Discussion Top


The outcomes of this study indicate that the visual outcomes at 6-8 weeks following conventional phacoemulsification and IOL implantation was not different from FLACS during the initial six months of adopting this new technology at KKESH. Variations in the visual outcomes following FLACS and conventional surgery were not influenced by the operating surgeon or severity of cataract. The intraoperative and postoperative complications of both types of surgeries were limited. However, the time required for FLACS was greater than that required for conventional cataract surgery.

Our study demonstrates that there is no statistically significant difference in visual outcomes following these two procedures. This outcome is similar to a previous study that evaluated the implantation of a presbyopic IOL with FLACS and found no difference in vision compared to conventional surgery and presbyopic IOL implantation. [13] Filkorn et al. suggested that precise anterior capsulorrhexis of 5 mm by laser could result in more precise positioning of the IOL and therefore provide better postoperative visual acuity. However, their study had small sample size and eyes with long axial lengths. Additionally, the authors concluded that the changes may be subtle and difficult to interpret based on differences in postoperative visual acuity. [14] We did not measure lens tilt and lens decentration and the higher order aberrations postoperatively and therefore cannot determine if there were subtle differences in visual quality. Visual acuity could also be affected by damage to different refractive surfaces of the eye especially the corneal endothelium. [9] More endothelial damage occurs with corneal edema especially while managing a hard cataract. [15] Less phacoemulsification energy would result in better visual acuity in eyes undergoing FLACS. We had only one eye with grade III nucleus, which underwent conventional phacoemulsification surgery. Hence, the effect of the phacoemulsification energy is less likely to be the cause of corneal damage and postoperative visual acuity in our study. FLACS also results in less intraocular manipulation and which can result in fewer alterations in macular morphology compared to conventional phacoemulsification surgery. [7],[16] Differences between conventional surgery and FLACS in terms of macular morphology is debatable. [17] The changes reported in the very early postoperative period may not reflect a difference in long-term outcomes between FLACS and conventional surgery.

Femtosecond laser assisted cataract surgery has been reported to cause decreased higher order aberrations, less lens tilt, less lens dislocation and more accurate prediction of postoperative refractive error. [14] However, these differences were small and may be difficult to demonstrate.

Including experienced surgeons in this study could explain the low complication rate found here. The low prevalence of Fuchs endothelial dystrophy in the Saudi population compared to that documented in some high-risk populations could be another explanation for the low complication rate in our study. [18],[19] The complications rate reported by Roberts et al. in their initial series of FLACS was high. [20] Capsular block syndrome is a complication that is associated to FLACS. [21] There were no cases of capsular block syndrome in the current study. Perhaps careful hydrodissection by experienced surgeons who were aware of possible complication avoided this complicated.

In the current study, we found an increase in the surgical time for patients who underwent FLACS, even without including the time spent on the application of the laser. Takács et al.[9] also showed similar outcomes. However, with experience this difference between FLACS and conventional surgery decreased. Previous studies demonstrated a reduction of effective phacoemulsification time (EPT) in FLACS. [22] In the current study, we did not note the time required for phacoemulsification. Therefore, comparison of the efficiency in reducing surgical time between two groups should be interpreted with caution. Although surgeons were very experienced in the conventional phacoemulsification surgery, the novelty of FLACS and its demonstration to fellows and residents may have likely increased surgical time. Additionally, to avoid capsular block syndrome the surgeons might have avoided aggressive hydrodissection. This could have resulted in inadequate mobilization of the lens nucleus that could slow the surgery considerably.

There are some limitations to this study. For example, the retrospective design of the study has some associated limitations. Indicators for corneal status before and after surgery were not available. The grade of cataract was evaluated subjectively with a slit lamp and using the lens opacities cataract grading scale (LOCS). [23] The pentacam nucleus grading system (PNS) is an objective method for defining lens density. It has been shown to correlate well with the subjective (LOCS) that was used in this study. Because each surgeon may have a slightly different subjective evaluation of nuclear density, the objective PNS values would have been superior in terms of predicting which surgeries would require greater phacoemulsification time. [24] Using the phacoemulsification energy in the eye for a longer time could result in more free radical formation and increased endothelial cell damage. [25] We did not measure lens tilt, decentration or higher order aberrations, which may be different between the two groups. These parameters are better controlled in FLACS. [9] This could have resulted in an underestimation of the complications in the conventional group. The ability to perform corneal incisions was not available with our femtosecond platform; the use of the femtolaser in performing this step of the cataract surgery could not be evaluated. Corneal incisions to enter the eye have been shown to be stable and precise. [26] They can be made in a reproducible fashion. Their superiority in terms of wound sealing and therefore safety has not been demonstrated.

Corneal incisions with the femtolaser can be used to create arcuate keratotomy (AK) incisions to reduce postoperative astigmatism. [27] If these incisions had been used, we should have shown a difference in postoperative uncorrected visual acuity in the FLACS group. In our institution, there is no financial inhibition in the use of toric IOLs. They were used as needed. Our results suggest that AK with the femtosecond laser may not provide a benefit in the face of unrestricted toric IOL use.

Literature has shown a bias in publications with commercial sponsorship [28],[29] Therefore, before ophthalmologists and eye care units procure expensive equipment for FLACS, independent researchers should study the short-term and long-term outcomes prospectively and evaluate the cost effectiveness of FLACS as advocated by Chen. [6]

Our attempt to compare outcomes of the initial cases of FLACS to conventional surgery with IOL implantation revealed no significant advantage. However, prospective studies and inclusion of parameters demonstrating corneal status, phacoemulsification energy and long-term outcomes are recommended.

 
   References Top

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