A more expensive and time-consuming way to perform cataract surgery cannot be justified without its providing significant benefits to patients. To address where femtosecond laser cataract surgery might add value, this article reviews the current outcomes of cataract surgery from the standpoint of safety.
Femtosecond laser cataract technology automates several steps of the cataract procedure. These include the primary and sideport corneal incisions, astigmatic keratotomy, the continuous circular capsulotomy, and nuclear fragmentation and softening. Compared with manually performing these same maneuvers, the femtosecond laser theoretically could offer greater precision and reproducibility. Until we surgeons have the outcomes of a sufficient number of peer-reviewed studies, we are left to ponder what the femtosecond laser's potential impact on safety and surgical complications might be.
One potential benefit of a more precise and reproducible incision would be greater wound integrity. The possible correlation between a rising postsurgical endophthalmitis rate since 1992 and the increasing utilization of clear corneal incisions was highlighted by Taban and coauthors in 2005.1 This observation raised the controversial question of whether clear corneal incisions increased the risk of endophthalmitis relative to scleral pocket incisions because of a higher incidence of subclinical wound leak with the former. Lacking any randomized, prospective, comparative trials, retrospective studies have provided the only data addressing this question.2,3 A compelling cohort study by Wallin and colleagues in 2005 reported on 27 consecutive cases of endophthalmitis occurring at a single institution (Utah).4 They determined that several factors significantly increased the statistical risk of endophthalmitis at their institution. Failure to use any antibiotic on the same day as surgery increased the risk of endophthalmitis fivefold, and zonular or posterior capsular rupture increased the risk 17-fold. The single most dangerous factor was a leaking incision, which led to a 44-fold increase in endophthalmitis.
Based on the available evidence, many would agree that clear corneal incisions are less forgiving than scleral pocket incisions with respect to poor wound construction and that the risk of transient wound leak increases with wider incisions.5 Along with astigmatic control, improved incisional integrity is one advantage cited by proponents of microincisional cataract surgery. Regardless of size, precise and proper wound construction is certainly important for optimizing the wound's integrity. Newer accommodating IOL technologies will at least initially challenge us with the requirement for larger cataract incisions.6 Sutures and tissue adhesives will allow us to safely increase the size of our clear corneal incisions, and the femtosecond laser could prove to be advantageous in this regard as well.
Continuous curvilinear capsulotomy
Long acknowledged by many as the most important step of our phaco procedure, the capsulorhexis offers many benefits. By allowing us to trap and encapsulate the optic and both haptics, the capsulorhexis virtually ensures the IOL's centration.7,8 An overlapping capsulorhexis enables the capsular bag to envelop the optic with a shrink wrap effect, by which the optic's sharp posterior edge will kink the posterior capsule.9,10 This mechanical lens-epithelial cell barrier reduces the incidence of secondary membrane formation. One of the most important benefits of a capsulorhexis, however, is that of safety. Like an elastic waistband, the capsulorhexis can stretch without tearing during the multitude of maneuvers to which the capsular bag is subjected during cataract surgery. In contrast, a single radial tear significantly increases the risk of wraparound extension into the posterior capsule.11 Table 1 shows data on the incidence of anterior capsular tears reported in four contemporary studies. 11-14 Robert H. Osher, MD, published the lowest rate of anterior capsular tears, 0.8%, based on his series of more than 2,600 consecutive eyes.11 The incidence of tears occurring during the creation of the capsulorhexis was 0.5%. Of note is that 48% of his anterior capsular tears eventually extended into the posterior capsule, and 19% of cases with a torn capsulorhexis required an anterior vitrectomy. This study suggests that the rate of anterior capsular tears is reasonably low in the hands of an expert surgeon. If it occurs, however, the risk of significant complications is very high in even the most experienced hands. At the other end of the spectrum is the experience of residents reported by Unal and colleagues.13 The capsulorhexis is consistently cited by residents as one of the most difficult steps to master.15 The rate of torn or irregular capsulorhexes in Unal's series was 5% and 9%, respectively. The overall rate of posterior capsular rupture and vitreous loss was 6.4%.13
Posterior capsulAR rupture and vitreous loss
Table 2 lists 13 studies of vitreous loss rates in nonresident series published between 1999 and 2009.16-28 Excluding the exceptionally low rate of 0.2% reported by Howard Gimbel, MD,20 the rate of vitreous loss consistently ranges from 1% to 4%. Table 3 lists eight studies of vitreous loss rates among residency programs that were published from 2002 to 2010.15,29-35 With the exception of one study, the rates ranged from 3% to 6%. The best current data on vitreous loss rates come from three recent studies of large patient populations. Narendran and coauthors' 2009 report on the Cataract National Dataset audit of 55,567 operations from the United Kingdom reported a 1.9% rate of vitreous loss.36 Greenberg and colleagues' 2011 published study of 45,082 US Veterans Administration hospital cataract surgeries found a 3.5% rate of vitreous loss.37 Finally, in 2011, Lundstrom and coauthors reported on all cataract surgeries performed at 52 centers composing the Swedish National Register during the period of 2002 to 2009.38 From a total of 602,533 cataract procedures, the incidence of capsular complications was 2.1%. Assuming that the Greenberg data would have included many resident surgeries, it appears that 2% is the best representative estimate of the capsular complication rate for large populations of practicing surgeons.
Ultrasound Power AND Endothelial Cell Loss
A number of studies have shown a reduction in ultrasound energy with a phaco chop method compared with divide and conquer.39-42 The correlation of phaco chop with reduced endothelial cell loss is less consistent in the literature.40,43,44 Part of the variability in the results from these studies undoubtedly relates to the varying density of the nuclei encountered. For example, Park and coauthors compared phaco chop to stop-and-chop in a bilateral eye study involving 51 patients.45 There was no statistical difference in mean effective phaco time for moderately dense nuclei; however, with dense nuclei, there was a statistically significant reduction in mean effective phaco time with chopping (P < .01). The specific comparison of stop-and-chop to prechopping may be more relevant in assessing the femtosecond laser's potential benefit. Pereira and coauthors found that prechopping significantly reduced effective phaco time and phaco power in a small prospective trial of 50 eyes.46
Despite chopping's reported advantages, in Leaming's 2010 survey of ASCRS members, only 32% of respondents were performing phaco chop compared with 62% who were performing divide and conquer.47 The fact that the phaco chop technique is generally more difficult to learn may be an important factor underlying these statistics. Reducing ultrasound time by prechopping and softening the nucleus is an important potential benefit of laser cataract surgery. The denser the nucleus is, the greater the ultrasound reduction should be, and the more likely a clinically significant difference in endothelial cell loss would be found.
Modern cataract surgery is an extraordinarily successful operation with very low rates of complications. The femtosecond laser has the potential to improve outcomes and reduce complications for many surgeons, but comparative studies are needed to determine if this is indeed true.
Parts of this article appear in Dr. Chang's chapter in the forthcoming textbook, Femtosecond Laser Refractive Cataract Surgery.
David F. Chang, MD, is a clinical professor at the University of California, San Francisco, and is in private practice in Los Altos, California. His consulting fees for Abbott Medical Optics Inc., Alcon Laboratories, Inc., and LensAR Inc. are donated to the Himalayan Cataract Project and Project Vision. Dr. Chang may be reached at (650) 948-9123; email@example.com.
- Taban M, Behrens A, Newcomb RL, et al. Acute endophthalmitis following cataract surgery: a systematic review of the literature. Arch Ophthalmol. 2005;123:613-620.
- Cooper BA, Holekamp NM, Bohigian G, Thompson PA. Case-control study of endophthalmitis after cataract surgery comparing scleral tunnel and clear corneal wounds. Am J Ophthalmol. 2003;136:300-305.
- Lertsumitkul S, Myers PC, O'Rourke MT, Chandra J. Endophthalmitis in the western Sydney region: a case-control study. Clin Experiment Ophthalmol. 2001;29:400-405.
- Wallin T, Parker J, Jin Y, et al. Cohort study of 27 cases of endophthalmitis at a single institution. J Cataract Refract Surg. 2005;31:735-741.
- Nichamin LD, Chang DF, Johnson SH, et al. American Society of Cataract and Refractive Surgery Cataract Clinical Committee. ASCRS White Paper: what is the association between clear corneal cataract incisions and postoperative endophthalmitis? J Cataract Refract Surg. 2006;32:1556-1559.
- Bohórquez V, Alarcon R. Long-term reading performance in patients with bilateral dual-optic accommodating intraocular lenses. J Cataract Refract Surg. 2010;36:1880-1886.
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- Lundstrom M, Barry P, Leite E, et al. 1998 European Cataract Outcome Study: report from the European Cataract Outcome Study Group. J Cataract Refract Surg. 2001;27:1176-1184.
- Ionides A, Minassian D, Tuft S. Visual outcome following posterior capsule rupture during cataract surgery. Br J Ophthalmol. 2001;85:222-224.
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- Tan JHY, Karwatowski WSS. Phacoemulsification cataract surgery and unplanned anterior vitrectomy: is it bad news? Eye. 2002;16:117-120.
- Chan FM, Mathur R, Ku JJK, et al. Short-term outcomes in eyes with posterior capsule rupture during cataract surgery. J Cataract Refract Surg. 2003;29:537-541.
- Androudi S, Brazitikos PD, Papadopoulos NT, et al. Posterior capsule rupture and vitreous loss during phacoemulsification with or without the use of an anterior chamber maintainer. J Cataract Refract Surg. 2004;30:449-452.
- Hyams M, Mathalone N, Herskovitz M, et al. Intraoperative complications of phacoemulsification in eyes with and without pseudoexfoliation. J Cataract Refract Surg. 2005;31:1002-1005.
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