Textbook of refractive laser assisted cataract surgery (re lacs)


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Textbook of refractive laser assisted cataract surgery (re lacs)

  1. 1. 9R.R. Krueger et al. (eds.), Textbook of Laser Refractive Cataract Surgery,DOI 10.1007/978-1-4614-1010-2_2, © Springer Science+Business Media, LLC 2013As modern small incision cataract surgery is one ofthe most successful operations in all of medicine,how much we can hope to further improve results?Adopting a more expensive and time-consumingway to perform the procedure cannot be justifiedwithout providing significant benefits to the patient.To contemplate the question of where a new tech-nology might add value, this chapter assesses ourcurrent outcomes of cataract surgery from two van-tage points—safety and refractive outcomes.Potential for Improving SafetyFemtosecond (FS) laser cataract technologyautomates several delicate and critical steps ofthe cataract procedure. These include the pri-mary and side-port corneal incisions, astigmatickeratotomy, the continuous circular capsulo-tomy, and nuclear fragmentation and softening.When compared to manual performance ofthese same functions, we would expect that aFS laser should offer greater precision andreproducibility. As only a handful of peer-reviewed outcome studies are available at thistime (Summer, 2011), we are left to ponderwhat the laser technology’s potential impact onsafety and complications will be?Clear Corneal IncisionsA more precise and reproducible incision wouldimprove wound integrity. The possible correla-tion of an increasing postsurgical endophthalmi-tis rate since 1992 with increasing utilization ofclear corneal incisions was highlighted by Tabanand coauthors in 2005 [1]. This observationraised the controversial question of whetherclear corneal incisions increased the endophthal-mitis risk relative to scleral pocket incisions,because of a higher incidence of subclinicalwound leak. Lacking any randomized prospec-tive comparative trials, retrospective studieshave provided the only data addressing thisquestion [2, 3]. One compelling study wasWallin and coauthors’ 2005 cohort study of 27consecutive cases of endophthalmitis occurringat a single institution (Utah) [4]. They deter-mined that several factors significantly increasedthe statistical risk of endophthalmitis at theirinstitution. Failure to use any antibiotic on thesame day as surgery increased the endophthal-mitis risk five-fold, while zonular or posteriorcapsular rupture increased the endophthalmitisrisk 17-fold. However, the single most danger-ous factor was an incision leak, which led to a44-fold increase in endophthalmitis.Based on the available evidence, many wouldagree that clear corneal incisions are less forgiv-ing than scleral pocket incisions with respect topoor wound construction both during and aftersurgery, and that the risk rises with increasinglywider incisions [5]. Along with astigmatismD.F. Chang, M.D. ()762 Altos Oaks Drive, Suite 1,Los Altos,CA 94024, USAe-mail: dceye@earthlink.net2Current Outcomes with CataractSurgery: Can We Do Better?David F. Chang12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758596061
  2. 2. 10 D.F. Changcontrol, improved incision integrity is oneadvantage cited by proponents of micro-inci-sional cataract surgery. Regardless of size, pre-cise and proper wound construction is certainlyimportant for optimizing wound integrity.Newer accommodating IOL technologies willchallenge us with the requirement for largercataract incisions [6]. Sutures and tissue adhe-sives will allow us to safely increase the size ofour clear corneal incisions, and the FS laser mayprove to be advantageous in this regard as well.Continuous Curvilinear CapsulotomyLong acknowledged by many as the single mostimportant step of our phaco procedure, the cap-sulorhexis offers many benefits. By allowing usto trap and encapsulate the optic and both hap-tics, IOL centration is virtually assured [7, 8].An overlapping capsulorhexis enables the cap-sular bag to envelope the optic with a shrinkwrap effect, by which a sharp posterior opticedge will kink the posterior capsule [9, 10]. Thismechanical lens epithelial cell barrier reducesthe incidence of secondary membrane forma-tion. One of the most important benefits of acapsulorhexis, however, is that of safety. Likean elastic waistband, the capsulorhexis canstretch without tearing during the multitude ofmaneuvers to which the capsular bag is sub-jected during cataract surgery. In contrast, asingle radial tear significantly increases the riskof wraparound extension into the posteriorcapsule [11].Table 2.1 shows data on the incidence of ante-rior capsule tears reported from four contempo-rary studies [11–14]. The lowest published rate ofanterior capsular tears comes from Bob Osher’spersonal series of more than 2,600 consecutiveeyes, which was 0.8% [11]. The incidence oftears occurring during the capsulorhexis step was0.5%. Of note was the fact that 48% of his ante-rior capsular tears eventually extended into theposterior capsule and 19% of cases with a torncapsulorhexis required an anterior vitrectomy.This study suggests that the rate of anterior cap-sular tear is reasonably low in the hands of anexpert surgeon, but that if it occurs, the risk ofsignificant complications is very high in even themost experienced hands.At the other end of the spectrum is the residentexperience reported by Unal and coauthors [13].The capsulorhexis is consistently cited by resi-dents as one of the most difficult steps to master[15]. The rate of torn capsulorhexis in the Unalseries was 5% and of irregular capsulorhexis was9%. The overall rate of posterior capsule ruptureand vitreous loss was 6.4% [13].Posterior Capsule Ruptureand Vitreous LossTable 2.2 and Fig. 2.1 list 13 studies of vitreousloss rates in non-resident series published dur-ing the decade between 1999 and 2009 [16–28]. Excluding Howard Gimbel’s exceptionallylow rate of 0.2% [20], the vitreous loss ratesTable 2.1  Incidence of anterior capsule tears [11–14]Study Date AC tear (%) NMuhtaseb 2004 2.8 1,000Marques 2006 0.8 2,646Unal 2006 5.0   296Olali 2007 5.6   358[AU1]Table 2.2  Published vitreous loss rates—1999–2009(0.2–4.4%) [16–28]Author Published % VitreouslossStudy sizeDesai 1999 4.4 18,454Martin 2000 1.3   3,000Lundstrom 2001 2.2   2,731Ionides 2001 2.9   1,420Gimbel 2001 0.2 18,470Tan 2002 3.6   2,538Chan 2003 1.1   8,230Androudi 2004 4.0    543Hyams 2005 2.0   1,364Ang 2006 1.1   2,727Zaidi 2007 1.1   1,000Mearza 2009 2.7   1,614Agrawal 2009 1.6   6,5646263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124t1.1t1.2t1.3t1.4t1.5t1.6t2.1t2.2t2.3t2.4t2.5t2.6t2.7t2.8t2.9t2.10t2.11t2.12t2.13t2.14t2.15t2.16t2.17
  3. 3. 112  Current Outcomes with Cataract Surgery: Can We Do Better?20,00015,00010,0005,0002,5007,50012,50017,5000 1 2 3 4 5Vitreous loss, %0StudysizeDesai1999Androudi2004Tan2002Ionides2001Mearza2009Lundstrom2001Hyams2005Zaidi2007Ang2006Martin2000Agrawal2009Chan2003Gimbel2001Fig. 2.1  Studies of vitreous loss rates in non-residentseries published during the decade between 1999 and2009 [16–28]200015001000500250750125017501 2 3 4 5 6 7 8Vitreous loss, %0StudysizeBlomquist2002Carricondo2010Lee2009Dooley2006Rutar2009Bhagat2007Pot2008Blomquist2010Fig. 2.2  Studies of vitreous loss rates among residencyprograms that were published from 2002 to 2010 [15,29–35]consistently range from 1 to 4%. Table 2.3 andFig. 2.2 list eight studies of vitreous loss ratesamong residency programs that were publishedfrom 2002 to 2010 [15, 29–35]. With the excep-tion of one study, these rates consistentlyranged from 3 to 6%. The best current pub-lished data on vitreous loss rates come fromtwo recent studies of large patient populations.Narendran and coauthors’ 2009 report on theCataract National Dataset audit of 55,567operations from the United Kingdom (UK)reported a 1.9% rate of vitreous loss [36].Greenberg and coauthors’ 2010 publishedstudy of cataract surgery in 45,082 US VeteransAdministration Hospital cataract surgeries hada vitreous loss rate of 3.5% [37].Ultrasound Power/Endothelial Cell LossA number of studies have shown a reduction inultrasound energy when employing a phaco chopmethod compared to divide and conquer [38–41]. The correlation of phaco chop with reducedendothelial cell loss is less consistent in the lit-erature [39, 42, 43]. Part of the variability of theresults from these studies undoubtedly relates tothe varying density of the nuclei encountered.For example, Park and coauthors comparedphaco chop to stop-and-chop in a bilateral eyestudy involving 51 patients [44]. There was nostatistical difference in mean effective phacotime (EPT) for moderately dense nuclei; how-ever, with dense nuclei, there was a statisticallysignificant reduction in mean EPT with chop-ping (P < 0.01). The specific comparison of stopand chop to pre-chopping may be more relevantin assessing the FS laser’s potential benefit.Pereira and coauthors found that pre-choppingsignificantly reduced effective phaco time andphaco power in a small prospective trial of 50eyes [45].Despite these reported advantages to chop-ping, the 2010 Leaming survey of ASCRS mem-bers reported that only 32% of respondents wereperforming phaco chop, compared to 62% whowere performing divide-and-conquer. The factTable 2.3  Published vitreous loss rates residents—2002–2010 (1.3–6.1%) [15, 29–35]Author Published % Vitreous loss Study sizeBlomquist 2002 4.5 1,400Dooley 2006 4   100Bhagat 2007 5.4   755Pot 2008 1.3   982Rutar 2009 3.1   320Lee 2009 4.9   226Carricondo 2010 6.1   261Blomquist 2010 3.2 1,833125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168t3.1t3.2t3.3t3.4t3.5t3.6t3.7t3.8t3.9t3.10t3.11
  4. 4. 12 D.F. Changthat the phaco chop technique is generally moredifficult to learn may be an important factorunderlying these statistics. Reducing ultrasoundtime by pre-chopping and softening the nucleusis an important potential benefit of FS laser cata-ract surgery. The denser the nucleus, the greaterthe ultrasound reduction should be, and themore likely a clinically significant difference inendothelial cell loss would be found.Potential for ImprovingRefractive OutcomesSpherical Equivalent AccuracyMany factors must be successfully managed toachieve pseudophakic emmetropia. A majoradvance has been in the more accurate determi-nation of axial length with non-contact, partialcoherence interferometry [47–49]. Two variableIOL power calculation formulae have been suc-cessfully used for decades [50–52]. Moreadvanced formulae, such as those developed byHaigis and Holladay, incorporate additional vari-ables in an effort to better predict the effectivelens position [53]. Table 2.4 summarizes six pub-lished studies that analyze refractive accuracy[49, 54–58]. Some of these series employed con-tact A-scan biometry, while others employed par-tial coherence interferometry. Even in the studywith the best results, 25% of eyes fail to refract towithin 0.5 D of the intended spherical equivalenttarget postoperatively.The one important variable that cannot bemeasured in advance is the final axial restingposition of the IOL optic—the so called, effec-tive lens position (ELP). Calculating a surgeon’spersonalized A-constant is an effort to optimizethe ELP prediction based on variables in indi-vidual surgical techniques. In addition to capsu-lar bag fixation of the IOL, the primary surgicalvariable that affects ELP is the diameter andshape of the capsulorhexis [59–61]. The gener-ally accepted surgical objective is a round capsu-lorhexis that overlaps the optic edge for all 360°of its circumference. This means that as the cap-sular bag shrinks and contracts postoperatively,the capsular forces are uniformly and symmetri-cally balanced in all three dimensions. A largerdiameter capsulorhexis that is all or partially“off ” the optic edge should permit the optic tomove slightly anterior to the position of one con-strained by a completely overlapping anteriorcapsular rim.Accommodating IOL designs may imposeadditional requirements for capsulorhexis diame-ter and shape. The ELP of a hinged optic, such aswith the Crystalens, would be expected to varywith the capsulorhexis diameter. If one assumes apreferred diameter of 5.0 mm, a smaller diametercapsulorhexis will contract more and may dis-place the optic more posteriorly. In contrast, alarger diameter capsulorhexis should allow theoptic to shift more anteriorly. Studies will beneeded to determine whether a FS laser capsulo-tomy is able to improve refractive outcomes onthe basis of greater ELP predictability. Finally,there is one special complication that is unique topremium refractive IOLs—that of a patient receiv-ing a well-positioned monofocal IOL, but not thetoric, multifocal, or accommodating IOL thatthey strongly preferred. For example, with thesynchrony dual optic accommodating IOL, theTable 2.4  Hitting emmetropia [54–59]Author N Biometry % Within 0.50 D % Within 1.00 DLanders (2009)    55 IOLMaster 75 93Immersion U/S 49 85Kim (2009)    30 Contact U/S 70 93Lim (2009)   100 Contact U/S 45 83Gale (2009) – IOLMaster – 80–87Eleftheriadis (2003)   100 IOLMaster – 96Murphy (2002) 1,676 Contact U/S 45 72Mean 57 87169170171172173174175176177178179180181182183184185186187188189190191192193194195196197198199200201202203204205206207208209210211212213214215216217218219220221222223224225226227228229230231232233234235236237238t4.1t4.2t4.3t4.4t4.5t4.6t4.7t4.8t4.9t4.10
  5. 5. 132  Current Outcomes with Cataract Surgery: Can We Do Better?anterior optic shifts forward with accommodativeeffort [6]. If the capsulorhexis does not completelyoverlap the anterior optic edge, the 5.0 mm diam-eter anterior optic may partially dislocate out ofthe bag and into the ciliary sulcus. A capsulor-hexis that is too large or eccentric in shape istherefore a contraindication to implanting the syn-chrony accommodating IOL. A torn capsulorhexisis also a contraindication to using the Crystalens,in my opinion, because of the significant potentialfor subluxation. A radial capsulorhexis tear alsoincreases the potential for single and three-pieceIOL decentration, and may be problematic for amultifocal or toric IOL where proper opticalalignment is more critical. Although they mightattain excellent corrected visual acuity with anintracapsular monofocal IOL, these aforemen-tioned patients are often emotionally distraught athaving permanently lost the opportunity to receivethe premium refractive IOL that they had selectedpreoperatively.Astigmatism ManagementThe number of cataract surgical patients withpreoperative corneal astigmatism has beendetermined from several studies. A publishedstudy of more than 23,000 eyes found that 8% ofpatients had at least 2.0 D of corneal astigma-tism preoperatively [62]. The percent of eyeswith at least 1.0 and 0.5 D of preoperative cor-neal astigmatism were 36 and 74% respectively.This correlated well with a study of more than4,500 eyes in which 35% of eyes had at least1.0 D, and 22% had at least 1.5 D of preopera-tive corneal astigmatism [63].Incisional astigmatic keratotomy (AK) is apopular method of simultaneously reducing pre-operative corneal astigmatism at the time of cata-ract surgery [64]. There is a relative dearth ofpublished studies on the efficacy of this methodin conjunction with phaco. Carvalho and coau-thors found a statistically significant reduction inmean topographic astigmatism from 1.93 ± 0.58 Dpreoperatively to 1.02 ± 0.60  D postoperativelyusing limbal relaxing incisions in 25 eyes [65].Mingo-Botín and coauthors compared toric IOLsto incisional astigmatic keratotomy in 40 eyesundergoing cataract surgery who were random-ized to either technique of astigmatism reduction[66]. The mean reduction in keratometric astig-matism was 0.58 D (30% of the preoperative cor-neal astigmatism) in the 20 eyes receiving AK,and there was with a statistically significantreduction in mean pre-op refractive astigmatism(pre-op −2.17 ± 1.02; post-op −1.32 ± 0.60;p = 0.001). However, the residual refractive astig-matism was £1.0  D in only 8/20 eyes (40%)receiving AK, compared to 18/20 eyes (90%)receiving a toric IOL. Poll and coauthors achieveda mean 0.46 D of postoperative astigmatism withastigmatic keratotomy in 115 eyes undergoingcataract surgery, which was comparable to toricIOL results in their series [67].The largest reported series of eyes undergoingastigmatic keratotomy combined with phaco isfrom Gills, and is shown in Fig. 2.3 [68]. He ana-lyzed 358 eyes with mild to moderate preopera-tive astigmatism, of which 74% had more than1.0  D of astigmatism. The mean preoperativeastigmatism of 1.59 D was reduced to a mean of0.99  D postoperatively. Sixty-five percent ofthese treated eyes had <1 D of keratometric cyl-inder postoperatively and only 23% had <0.5 Dof astigmatism postoperatively.In the 2010 Leaming survey, 67% of respon-dents most often use a toric IOL and 18% ofrespondents most often use astigmatic kerato-tomy to treat pre-existing astigmatism in their7060502004010309080100PercentPre-opPost-op< 0.5 < 1 < 1.5 < 2Distribution of K Cylinder23%26%65%59%83%75%92%0%65% < 1 D23% < 0.5 D75% < 1 Dn = 358Fig. 2.3  Gills LRI data. n = 358, Mean pre-op cyl 1.59 D(mild-moderate astigmatism) [68]239240241242243244245246247248249250251252253254255256257258259260261262263264265266267268269270271272273274275276277278279280281282283284285286287288289290291292293294295296297298299300301302303304305306307308309310311312313314315
  6. 6. 14 D.F. Changcataract patients [46]. Astigmatic keratotomywill always be plagued by an unavoidable vari-able—that of the individual tissue response to thecorneal relaxing incision. Nevertheless, it standsto reason that AK results will be more accurate ifthe depth, curvature, length, diameter and axialorientation of the incisions (upon which thenomograms are developed and based) are madeas reproducibly consistent as possible. It will beof great interest to see if FS laser astigmatic kera-totomy will fulfill this potential.Key Points 1. The most recent published cataract surgicalstudies estimate the rate of vitreous loss to be2–4%. 2. Thirty-five percent of cataract patients have atleast 1 D of corneal astigmatism.References 1. Taban M, Behrens A, Newcomb RL, et  al. Acuteendophthalmitis following cataract surgery: a system-atic review of the literature. Arch Ophthalmol. 2005;123:613–20. 2. 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  9. 9. Author QueriesChapter No.: 2 0001610159Queries Details Required Author’s ResponseAU1 Please check the caption of all tables.AU2 Please note that “Take Home Points” has been changed to “Key Points” throughout thebook to maintain consistency.AU3 As Refs. [49, 54] were identical the latter reference has been deleted and the subsequentreferences have been renumbered sequentially. Please check.
  10. 10. http://www.springer.com/978-1-4614-1009-6