Introduction

Literature Review

There is a growing body of investigation focused on minimally invasive bimanual microincision cataract surgery (MICS). The first reports of this technique published in peer-reviewed journals appeared in the mid-1970s and 1980s [1–4]. Agarwal is generally recognized as having created a renewed interest in this technique [5].

A series of cases of bimanual MICS was published in January 2002 which consisted of a noncomparative study of this procedure in 637 eyes [6]. The volume of publications on this subject has seen a considerable increase in the last 18 months. From 1995 through 2006, over 50 papers have featured bimanual, or biaxial, MICS. In 2007 and the first half of 2008, an additional 30 peer-reviewed papers have been published, addressing various topics.

Major Issues

The issues surrounding the debate between traditional, or microcoaxial, phacoemulsification and bimanual, or biaxial, microincision phacoemulsification are many. Within the published literature, these issues can be broken down into the following major groups:

1.Visual outcome: postsurgical best corrected visual acuity (BCVA), and change in astigmatism

2.Corneal/anterior chamber factors: corneal endothelial cell loss, postsurgical corneal swelling, and anterior chamber cell and flare

I. H. Fine ( )

Oregon Health & Science University, Drs. Fine, Hoffman and Packer, 1550 Oak Street, Suite 5, Eugene, OR 97401, USA e-mail:hfine@finemd.com

3.Incision-specific factors: thermal burn and incision leakage

4.Technical factors: effective phacoemulsification time (EPT) and total surgical time

Nearly all of the published studies examine one or more of these factors, either in a directly comparative setting or simply to determine the rates of these factors in biaxial MICS for comparison with historical levels in coaxial phacoemulsification. Some studies do provide data on other metrics specific to the particular aspect being studied, but these are widely variable and difficult or impossible to compare between studies [7]. We will focus on the above major issues in this review.

Major Studies

Many of the published papers on this subject use animal or cadaver eyes, are noncomparative, have significant confounding variables, or are simply opinion pieces or case reports. This leaves only a handful of studies which are considered seminal, high-quality papers. These are randomized, prospective, comparative studies conducted on human subjects by surgeons competent in the techniques being compared. Most have large sample sizes and minimal confounding variables. All were published in highly respected peer-reviewed journals. These studies are discussed individually and only statistically significant results are analyzed.

In January 2002, Tsuneoka et al. [6] published a paper evaluating thermal burn, astigmatism, and endothelial cell loss as a result of bimanual phacoemulsification using a 1.4 mm incision and a sleeveless phaco tip. This was the first large series studying bimanual phacoemulsification; 637 eyes were included.

Although noncomparative, it remains an important study. Approximately 5% of the cataracts had grade 4 or 5 nuclear density. The results showed a mean operating time of 8 min and 42 s. Not one case of thermal burn was reported. Three-month postsurgical follow-up was done in 312 eyes. Measured corneal endothelial cell density had decreased by 4.6% in eyes with a nuclear hardness of grade 1, 6.9% in eyes with grade 2, 10.8% in eyes with grade 3, and 15.6% in eyes with grade 4 and above. The authors considered these levels to be similar to cell loss with traditional, coaxial, phacoemulsification methods. Corneal astigmatism was 0.35D at postoperative week 1 and 0.18D at postoperative month 3, which was deemed to be far lower than postoperative astigmatism induced by standard phacoemulsification, despite enlargement of an incision up to 4 mm for IOL insertion. The authors concluded bimanual MICS to be at least as safe and effective as traditional methods, especially considering superior astigmatic results.

Jorge Alió, a pioneering surgeon with biaxial phacoemulsification, published the first large prospective randomized landmark study in November 2005, comparing bimanual MICS with regular coaxial phacoemulsification [8]. A total of 100 eyes with cataracts graded 2–4 were randomized to two groups, one receiving biaxial phaco from 1.5 mm incisions, and the other receiving coaxial phaco via a 2.8 mm incision. All other aspects of the surgeries were designed to be identical, including equipment settings, minimizing confounding variables. Key statistically significant results showed dramatic differences in estimated phaco time (EPT = total phacoemulsification time in seconds × average power percent used): 2.19 for biaxial and 9.3 for coaxial. Postsurgical astigmatic changes were significantly lower in bimanual MICS (0.433 vs. 1.20D in the coaxial group). Postoperative corneal endothelial cell loss, anterior chamber cell/flare, and visual acuity were statistically equal in both groups. As in the Tsuneoka et al. study, no signs of thermal burns were seen with either technique. The authors understandably concluded bimanual MICS to be safe, effective, and in many ways superior to coaxial techniques.

In 2006, Kurz et al. compared biaxial microincision (1.5 mm) and coaxial small-incision (2.75 mm) cataract surgery in a well-designed study of 70 randomized eyes [9]. A multitude of outcomes were measured. BCVA on postoperative day 1 showed a mean of 20/25 in the biaxial group and 20/33 in the coaxial group. Eight weeks after surgery, BCVA in the biaxial group was 20/20 versus 20/25 in the coaxial group, showing

notably better visual acuity outcomes in bimanual MICS. EPT times were measured to be greater than 3 s in 34% of bimanual patients and 68% of coaxial patients. Astigmatic changes were statistically similar (0.15 vs. 0.31D). Corneal endothelial cell losses were statistically equivalent in both groups (14–15%). Overall, using these and other metrics, the authors concluded bimanual phacoemulsification to be as efficacious as coaxial, and, in fact, superior in two aspects.

Cavallini et al. prospectively randomized 100 eyes in 50 patients to compare bimanual and coaxial phacoemulsification in a paper published in 2007 [10]. All cataracts were graded 2–4. Particularly interesting was that all 100 procedures were done using the same machine and by the same surgeon, who was quite capable at both methods. Multiple key metrics were recorded. The authors reported all metrics to be statistically equal, including EPT (3–5 s), corneal endothelial cell loss (10–12 cells/mm), and postsurgical astigmatism (<1D). Shorter surgical time was reported in the biaxial group (637 vs. 736 s). Less BSS was used in the biaxial technique. The authors concluded both methods to be safe and effective.

One must keep in mind that these studies did not address the primary benefits of biaxial technique (ability to interchange instruments by switching hands, iris management, separation of aspiration from irrigation, etc.). These studies and nearly all the published papers address measurable outcome metrics. Therefore, if biaxial phaco was deemed only equal to coaxial phaco by these measurements, it would still have tremendous benefit because of the fluidic advantages of separating aspiration from irrigation and eliminating competing fluid currents at the tip. Smaller incisions are also inherently less invasive.

Kahraman et al. published a well-designed prospective study with masked investigators to compare metrics of phacoemulsification outcomes 1 day and 3 months after surgery [11]. Thirty-three patients underwent cataract surgery, with bimanual phaco being performed in one eye and micro-coaxial (3.2 mm) in the other eye of each patient on the same day. The standard metrics for evaluating cataract surgery were recorded. The data showed no statistical differences between the two techniques, except that corneal thickness was increased on the first postoperative day in the biaxial group by 14 μm, ostensibly due to corneal swelling. This difference resolved at the second time point. The authors correctly concluded that bimanual MICS is safe and reproducible.

In June 2007, Cerma et al. performed standard coaxial in one eye and bimanual MICS in the fellow eye of 30 patients with 1 year follow-up in 26 patients [12]. In this study, EPT was significantly higher in the biaxial group (8.2 vs. 5.0 s). Corneal endothelial cell loss was also greater in the biaxial MICS group (8.82 vs. 6.00% cells/mm). BCVA was similar in both groups. The authors stated that the endothelial cell loss was well within safe limits and concluded that biaxial was a safe and effective method for cataract removal.

Yao et al. randomized 60 eyes to biaxial phaco with a 1.7 mm incision and coaxial phaco with 3.2 mm incisions [13]. This study was specifically designed to focus on surgically induced astigmatism and showed biaxial phaco to be equal or superior to coaxial phaco 1-month postoperatively with less astigmatic changes (0.78 vs. 1.29D). Mencucci et al. compared biaxial MICS with standard phacoemulsification in 80 eyes, using stop-and-chop in both groups [14]. Among several other metrics, there was no statistically significant difference in central corneal endothelial cell counts.

Again, these studies do not compare the overall superiority of either technique and do not address any surgical benefits of one technique over the other. All studies concluded BCVA and astigmatic changes to be equal or superior in biaxial phaco, but corneal endothelial cell loss was inconclusive or contradictory. All the major studies cited conclude that bimanual MICS is at least as safe and effective as coaxial methods. We believe that biaxial techniques are superior and that is especially true in challenging and complicated cases (see Chap. 3), many of which would be impossible to perform with coaxial procedures.

Negative Studies

As of mid-2008, the peer-reviewed literature contained less than ten papers which suggest that biaxial MICS may be an inferior technique, with their major finding being a negative outcome for biaxial phaco.

The Kahraman study showed increased corneal thickness due to swelling in the first postoperative day, but showed no other statistical differences [11]. The Cerma study reported that EPT and corneal endothelial cell loss was higher in the biaxial group [12]. It also reported similar BAVA at 1 year between the two groups.

In a comparative study in 2008, Praveen et al. compared 180 eyes randomized into three phacoemulsifi-

cation groups: standard coaxial, micro-coaxial, and biaxial [15]. The ingress of trypan blue dye into the eye was measured immediately after cortex removal and again at the end of surgery after stromal hydration. The study concluded that biaxial wounds allowed increased ingress intrasurgically immediately after cortex removal when compared to other groups. However, after stromal hydration, no statistical difference was found between the three groups.

The two rabbit studies compared wound damage and bacterial ingress and concluded coaxial and microcoaxial to be superior to biaxial in these areas [16, 17]. Two cadaver studies used small sample sizes (15 eyes and 6 eyes) to look at wound damage and temperature and concluded coaxial and micro-coaxial to be superior to biaxial in these areas [18, 19].

We have inadequate knowledge of construction and architecture of the biaxial incisions in these studies, but, as Fine has demonstrated utilizing optical coherence tomography (OCT), properly constructed microbiaxial incisions creates architecture that is self-sealable and stable [20, 21]. Finally, all of these investigators are novices at biaxial phaco and their initial experiences cannot be compared to other techniques that they have mastered over a period of decades.

References

1.Shock JP. Removal of cataracts with ultrasonic fragmentationandcontinuousirrigation.TransPacCoastOtoophthalmol Soc Annu Meet 1972; 53:139–144.

2.Girard LJ. Ultrasonic fragmentation for cataract extraction and cataract complications. Adv Ophthalmol 1978; 37: 127–135.

3.Shearing SP, Relyea RL, Loaiza A, Shearing RL. Routine phacoemulsification through a one-millimeter non-sutured incision. Cataract 1985; 2:6–10.

4.Hara T, Hara T. Endocapsular phacoemulsification and aspiration (ECPEA) – recent surgical technique and clinical results. Ophthalmic Surg 1989; 20(7):469–475.

5.Agarwal A, Agarwal S. No anesthesia cataract surgery. In: Agarwal S (ed.) Phacoemulsification, Laser Cataract Surgery, and Foldable IOLs. New Dehli, India: Jaypee Brothers, 1998, 144–154.

6.Tsuneoka H, Shiba T, Takahashi Y. Ultrasonic phacoemulsification using a 1.4 mm incision: clinical results. J Cataract Refract Surg 2002; 28(1):81–86.

7.Olson RJ, Jin Y, Kefalopoulos G, et al. Legacy AdvanTec and Sovereign WhiteStar: a wound temperature study. J Cataract Refract Surg 2004; 30:1109–1113.

8.Alio J, Rodriguez–Prats JL, Galal A, Ramzy M. Outcomes of microincision cataract surgery versus coaxial phacoemulsification. Ophthalmology 2005; 112(11):1997–2003.

9.Kurz S, Krummenauer F, Gabriel P, Pfeiffer N, Dick HB. Biaxial microincision versus coaxial small-incision clear cornea cataract surgery. Ophthalmology 2006; 113(10): 1818–1826.

10.Cavallini GM, Campi L, Masini C, Pelloni S, Pupino A. Bimanual microphacoemulsification versus coaxial miniphacoemulsification: prospective study. J Cataract Refract Surg 2007; 33(3):387–392.

11.Kahraman G, Amon M, Franz C, Prinz A, Abela-Formanek

C.Intra-individual comparison of surgical trauma after bimanual microincision and conventional small-incision coaxial phacoemulsification. J Cataract Refract Surg 2007; 33(4):618–622.

12.Crema AS, Walsh A, Yamane Y, Nosé W. Comparative study of coaxial phacoemulsification and microincision cataract surgery. One-year follow-up. J Cataract Refract Surg 2007; 33(6):1014–1018.

13.Yao K, Tang X, Ye P. Corneal astigmatism, high order aberrations, and optical quality after cataract surgery: microincision versus small incision. J Refract Surg 2006; 22(9 Suppl):S1079–S1082.

14.Mencucci R, Ponchietti C, Virgili G, Giansanti F, Menchini

U.Corneal endothelial damage after cataract surgery: microincision versus standard technique. J Cataract Refract Surg 2006; 32(8):1351–1354.

15.Praveen MR, Vasavada AR, Gajjar D, Pandita D, Vasavada VA, Vasavada VA, Raj SM. Comparative quantification of ingress of trypan blue into the anterior chamber after micro-

coaxial, standard coaxial, and bimanual phacoemulsification: randomized clinical trial. J Cataract Refract Surg 2008; 34(6):1007–1012.

16.Johar SR, Vasavada AR, Praveen MR, Pandita D, Nihalani B, Patel U, Vemuganti G. Histomorphological and immunofluorescence evaluation of bimanual and coaxial phacoemulsification incisions in rabbits. J Cataract Refract Surg 2008; 34(4):670–676.

17.Gajjar D, Praveen MR, Vasavada AR, Pandita D, Vasavada VA, Patel DB, Johar K, Raj S. Ingress of bacterial inoculum into the anterior chamber after bimanual and microcoaxial phacoemulsification in rabbits. J Cataract Refract Surg 2007; 33(12):2129–2134.

18.Berdahl JP, DeStafeno JJ, Kim T. Corneal wound architecture and integrity after phacoemulsification evaluation of coaxial, microincision coaxial, and microincision bimanual techniques. J Cataract Refract Surg 2007; 33(3): 510–515.

19.Osher RH, Injev VP. Microcoaxial phacoemulsification Part

1:laboratory studies. J Cataract Refract Surg 2007; 33(3): 401–407.

20.Fine IH, Hoffman RS, Packer M. Profile of clear corneal cataract incisions demonstrated by ocular (optical) coherence tomography. J Cataract Refract Surg 2007; 33(1): 94–97.

21.Fine IH, Hoffman RS, Packer M. Architecture of clear corneal incisions demonstrated by ocular coherence tomography. Highlights Ophthalmol 2007; 35(4):2–4; 6–9.