Corneal incision quality: Microincision cataract surgery versus microcoaxial phacoemulsification

ARTICLE

Corneal incision quality: Microincision cataract surgery versus microcoaxial phacoemulsification Bassam Elkady, MD, David Pin˜ero, PhD, Jorge L. Alio´, MD, PhD

PURPOSE: To use corneal optical coherence tomography (OCT) to evaluate the corneal incision quality in microincision cataract surgery (MICS) and microcoaxial phacoemulsification (microphaco). SETTING: Vissum-Instituto Oftalmolo´gico de Alicante, Alicante, Spain. METHODS: Eyes with cataract grade II to IV were randomized into 2 groups for MICS or microphaco. Corneal incision quality was analyzed using corneal OCT on the first postoperative day, week, and month using a purpose-developed protocol and an objective model. Corneal OCT parameters were incision and corneal thickness, incision angle, epithelial and endothelial sealing, incision coaptation, and Descemet detachment. Visual, refractive, corneal topography, and aberrometric data were analyzed. RESULTS: There were no statistically significant between-group differences in corneal thickness and incision angle quality, geometrically assessed using corneal OCT. Corneal edema was less with MICS than with microphaco (44% versus 87%) (PZ.002), as was corneal thickness in the 5.0 to 7.0 mm area (659.9 G 56.7 mm versus 697 G 80.6 mm) (PZ.06), but only at 1 day. At 1 month, prolateness for an 8.0 mm area was maintained in the MICS group. Corneal root-meansquare astigmatism and residual were slightly better with MICS (0.6 G 0.4 mm versus 0.9 G 0.6 mm, PZ.06; 0.6 G 0.2 mm versus 0.7 G 0.3 mm, PZ.05). Other OCT outcome parameters did not differ significantly between groups. CONCLUSIONS: Microincision cataract surgery and microphaco provided similarly good incision quality and optically neutral incisions; the MICS incision respected corneal prolateness more, with less corneal edema in the short term and less induced corneal aberrations in the long term. J Cataract Refract Surg 2009; 35:466–474 Q 2009 ASCRS and ESCRS

The trends toward reduction in incision size began in the early 1970s with the concept of small-incision phacoemulsification, introduced by Kelman.1 This development allowed further reduction in size from the 6.0 to 7.0 mm incisions of manual extracapsular cataract extraction to 3.4 mm and 2.8 mm incisions, which was the minimum size before the recent era of microincision cataract surgery (MICS).2 The desire to minimize incision size led to the biaxial technique, in which the use of irrigation and aspiration is divided; this requires a bare phacoemulsification tip.2 Two incisions and separation of function provide minimal operative stress to the cornea, with less anatomical and functional disturbances. Today, an incision of 1.5 mm or smaller can be used with MICS.3–5 However, although the nonprotected phaco tip can gently manipulate the cornea, there is a question of whether the loss of the cushioning effect of the sleeve traumatizes the cornea and produces poor-quality 466

Q 2009 ASCRS and ESCRS Published by Elsevier Inc.

incisions.6 In a previous study,7 we found that the bare tip used in MICS treats the cornea in a way that respects its anatomy, yielding good-quality, optically neutral incisions. The reduction in incision size provides many advantages by reducing the need for suturing, leading to more wound stability, a decrease in regular and irregular astigmatism (by avoiding corneal wound burn),6 and a decrease in corneal aberrations.7–11 In addition, smaller incisions have been associated with a significant decrease in postoperative intraocular inflammation and endophthalmitis,12,13 fewer wound-related complications, shorter surgical time, and faster postoperative rehabilitation.2,3 Smaller incisions also yield a lower incidence of vitreous loss, iris inclusion, and intraoperative floppy-iris syndrome; less wound leakage, inward14,15 or outward with subsequent macular edema; and fewer cases of expulsive hemorrhage.2,4,7,8 0886-3350/09/$dsee front matter doi:10.1016/j.jcrs.2008.11.047

MICROINCISION VERSUS MICROCOAXIAL PHACOEMULSIFICATION

These benefits can explain the new trends toward reducing the incision size using either of the 2 methods currently available for microincision lens surgery; that is, using a sleeveless tip (MICS) or using a protected (sleeved) tip (microphaco).8 The difference is that MICS is bimanual phacoemulsification with an incision of 1.2 mm, while microphaco is coaxial phacoemulsification with a 2.2 mm incision (L.J. Ronge´, ‘‘Step-by-Step Guide to Microphaco,’’ EyeNet January 2004, pages 23–24. Available at: http://development. aao.org/news/eyenet/cataract/cataract_jan_2004. htm. Accessed December 8, 2008; C. Guttman, ‘‘Coaxial Microphaco Considered a Significant Advance in Cataract Surgery,’’ Ophthalmology Times October 15, 2005, 30(20), pages 1, 22).16 The aim of this study was to compare the corneal incision of sleeved and sleeveless microincision phacoemulsification in terms of anatomical quality of the incision and changes in the optical corneal profile by imaging and objective analysis of the incision using corneal optical coherence tomography (OCT) and corneal aberrometry. PATIENTS AND METHODS Patients This prospective randomized cumulative interventional comparative case series comprised eyes with grade II to IV nuclear or corticonuclear cataract (Lens Opacities Classification System [LOCS] III classification17). Patients were interviewed for demographic data and confirmation of ocular, systemic, and medical histories. All patients signed an informed consent. The study followed the tenets of the Declaration of Helsinki stated in 2002.18 Ethical committee approval was obtained. Inclusion criteria were age between 40 years and 90 years, no history of eye surgery or glaucoma, a transparent central cornea, pupil dilation at the preoperative examination of at

Submitted: September 30, 2008. Final revision submitted: November 21, 2008. Accepted: November 23, 2008. From Vissum-Instituto Oftalmolo´gico de Alicante (Elkady, Pin˜ero, Alio´), Departamento de O´ptica, Farmacologı´a y Anatomı´a (Pin˜ero), Universidad de Alicante, Miguel Hernandez University (Alio´), Alicante, Spain; Ain Shams University (Elkady), Cairo, Egypt. No author has a financial or proprietary interest in any material or method mentioned. Supported in part by a grant from the Spanish Ministry of Health, Instituto Carlos III, Red Tema´tica de Investigacio´n en Oftalmologia, Subproyecto de Cirugia Refractiva y Calidad Visual (C03/13). Corresponding author: Jorge L. Alio´, MD, PhD, Research, Development, and Innovation Department, Vissum-Instituto Oftalmolo´gico de Alicante, Avenida de Denia s/n, Edificio Vissum, 03016 Alicante, Spain. E-mail: [email protected].

467

least 7.0 mm, absence of biomicroscopic signs of pseudoexfoliation, and normal fundus examination. Exclusion criteria were cataracts other than nuclear or corticonuclear and all cataracts higher than grade 4 (LOCS III17), eyes with more than 3.00 diopters (D) of astigmatism to exclude eyes in which astigmatic incisions would be necessary, and other ocular disease that might affect visual outcomes (eg, color vision disturbance, chronic uveitis) or contrast sensitivity function (high myopia, glaucoma, maculopathy). The eyes were randomly classified into 2 groups based on the type of the surgery. Eyes in the MICS group had biaxial bimanual phacoemulsification with an incision smaller than 2.0 mm. The microphaco group had microcoaxial phacoemulsification with a 2.2 mm incision.

Patient Examinations Preoperatively, a standard comprehensive ophthalmic examination was performed. The examination included clinical data, the refractive status of the eye, uncorrected visual acuity (UCVA) and best spectacle-corrected distance visual acuities (BSCVA) using Snellen charts (values expressed in decimal values), slitlamp evaluation, intraocular pressure (IOP) measurement by Goldmann applanation tonometry, lenticular status, stereoscopic biomicroscopy of the macula, and anterior corneal surface evaluation using the CSO topographer (Compagnia Strumenti Oftalmici). All postoperative examinations were performed by the same independent observer (B.A.K.), who did not perform any of the surgeries. The following protocol was used for the postoperative examinations: 30 minutes after surgery dclinical slitlamp examination with localization of the incision and confirmation that the incision was not leaking; 1 daydvisual acuity, IOP, slitlamp examination, Seidel test to check for incision leakage, and analysis of the corneal incision using corneal OCT; 1 weekdvisual acuity, refraction, IOP, slitlamp examination, and analysis of the corneal incision using corneal OCT; 1 monthdvisual acuity, refraction, IOP, slitlamp examination, analysis of the corneal incision using corneal OCT, corneal topography, and aberrometry.

Surgical Technique All surgeries were performed by the same surgeon (J.L.A.) using microincision sutureless phacoemulsification techniques. Topical anesthesia of preservative-free lidocaine 2% and mild sedation with midazolam was used in all cases. Adequate pupil dilation was obtained with intracameral mydriasis using 1.0 mL of a vial containing cyclopentolate 1.0% (1.0 mL), phenylephrine 10.0% (1.5 mL), lignocaine 2.0% (5.0 mL), and a balanced salt solution.

Biaxial Microincision Cataract Surgery A 1.4 mm clear corneal incision was made at the steepest corneal meridian with an Alio´ MICS diamond blade (Katena); this was the main incision for IOL implantation. A second, similar clear corneal incision was made at 90 degrees. An Infiniti phacoemulsification platform (Alcon Laboratories) was used. Surgery was performed with a 30-degree, 0.9-caliper phacoemulsification tip (microtip) with prechopping and hyperpulse (80 msec, 40%) mode. Microincision cataract surgery was performed following a previously described protocol.3,4,7

Microcoaxial Phacoemulsification A 2.2 mm clear corneal microincision was placed on the axis of the positive

J CATARACT REFRACT SURG - VOL 35, MARCH 2009

468

MICROINCISION VERSUS MICROCOAXIAL PHACOEMULSIFICATION

Figure 1. Optical coherence tomography image of a MICS incision showing the characteristic appearance of the incision with arcuate configuration.

Figure 2. Optical coherence tomography image of a MICS incision showing the model used in the study for measuring angle of the incision (white arrow).

corneal meridian using a stainless steel microkeratome. A 1.0 mm paracentesis was made 90 degrees apart with a calibrated knife (Alcon Laboratories). After the capsulorhexis was created, hydrodissection, nucleus rotation, prechopping, and phacoemulsification were performed using the Infiniti Vision System and a technique similar to that used in the MICS group. The only difference was that in the MICS group, the gas forced-infusion mechanism was used as a pump to pressurize the inflow of fluids for optimum anterior chamber stability; the mechanism was not used in the microphaco group.

Fluotest). The observer checked to determine whether outward or inward Seidel signs were present. Any epithelial or stromal alteration was recorded and analyzed. After biomicroscopic evaluation, corneal OCT was performed using the Visante system (Carl Zeiss Meditec AG). This device uses an infrared light of a 1310 nm wavelength to obtain interferometry scans of different anterior segment structures.19 The system is connected to a computer that has software with several options for image capturing and measurement. First, with the patient well positioned, the data were introduced into the software. Next, the ‘‘High Res Corneal’’ option was chosen to obtain accurate scans of the corneal structure. A complete transversal scan was obtained by asking the patient to fixate on an object located in the opposite direction of the corneal incision. A linear scan with the same orientation of the incision was used. The linear scan was rotated 10 degrees clockwise and 10 degrees counterclockwise to find the image with the best resolution. Then, the scanning was performed and an image acquired. All scans had a characteristic appearance with an arcuate configuration (Figure 1). After the image was obtained, 8 characteristics were determined. The first was the angle of the incision continuous variable, which is the angle formed between the line joining the epithelial and endothelial edges and the tangent line to the epithelial edge of the incision (Figure 2). The distances were measured, after which the angle was calculated with a simple trigonometric relation. Second was sealing of the epithelial edge, which was a dichotomous variable (sealed or not sealed) (Figure 3). Third was sealing of the endothelial edge (dichotomous variable; sealed or not sealed) (Figure 3). Fourth was the thickness of the cornea in the area of the incision and at 1.0 mm at each side of the incision. Fifth was

Intraocular Lens Implantation and Completion of Surgery Two types of IOLs were implanted: the Acri.Smart 48S and Acri.LISA 366D (both Acri.Tec GmbH). The Acri.Smart 48S is a monofocal IOL; the Acri.LISA 366D is a multifocal refractive–diffractive aspheric IOL that corrects aberration. Both are foldable MICS IOLs. The IOL was loaded in the adequate cartridge and then inserted in a hydraulic injector (Acri.Glide, Acri.Tec). In the MICS group, the incision was enlarged laterally at its internal side to approximately 1.8 mm with the diamond blade. The tip of the cartridge was introduced partially into the external part of the incision, after which the IOL was injected into the capsular bag. The proximal part was placed in the bag with a second instrument (Alio´ intraocular manipulator, Katena) inserted through the second incision. After the ophthalmic viscosurgical device was removed, the incisions were hydrated in both groups using a 30-gauge cannula (Alcon). Intraocular preservative-free cefuroxime 1.0% (0.1 cm3) was injected into the anterior chamber in all cases. No sutures were used in any eye in either group. Postoperative topical therapy included topical ofloxacin 0.3% (Exocin) and dexamethasone alcohol 0.1% (Maxidex). The corneal incision length was measured at the end of the procedure using a gauge caliper (Memmen-Steinert, American Surgical Instruments Co.) that measures from 1.00 mm to 4.00 mm in 0.10 mm increments. The tips of the caliper were applied to the inner lips of the incision to measure the length.

Protocol and Model for the Analysis of Corneal Incision Quality After surgery, patients were allowed to rest for 30 minutes. They were then examined by an independent observer at the slitlamp. The stability of the corneal incision was analyzed with slitlamp biomicroscopy, and its location was detected. Sealing of the corneal incision was analyzed using a fluorescein Seidel test comprising 3.0 mL of 2.5 mg fluorescein sodium plus 4.0 mg oxybuprocaine chloride (Colircusi

Figure 3. Optical coherence tomography image of a MICS incision showing sealed epithelial edge and gaped endothelial edge of the same incision (white arrows).

J CATARACT REFRACT SURG - VOL 35, MARCH 2009

469

MICROINCISION VERSUS MICROCOAXIAL PHACOEMULSIFICATION

Table 1. Patient demographics. Group Parameter

Figure 4. Optical coherence tomography image of a microphaco incision showing Descemet’s membrane detachment and endothelial bullae (white arrow).

the central corneal thickness (CCT) and mean thickness in the 2.0 to 5.0 mm area and 5.0 to 7.0 mm area of the cornea (mean values of the corneal OCT pachymetric map for each corresponding area). Sixth was the percentage of the incision length without coaptation in respect to the total length (Figure 3). Seventh was the percentage of eyes with Descemet membrane detachment (Figure 4). Eighth was the percentage of eyes with endothelial bulge or bullae (Figure 4).

Corneal Aberrometry Corneal aberrations were derived from the data of the anterior surface of the cornea obtained from the topography system. The CSO topography system software, EyeTop2005, converts the corneal elevation profile into corneal wavefront data using the Zernike polynomials with an expansion up to the 7th order. The system analyzes 6144 corneal points from a corneal zone between 0.33 mm and 10.00 mm with respect to corneal vertex. To evaluate changes in corneal aberrations, the root mean square (RMS) of the wave aberration for total, primary coma Z(3,G1), astigmatism Z(2,G2), and higher-order (HOA) aberrations with a 6.0 mm pupil diameter was studied preoperatively and 1 month postoperatively. Primary spherical aberration Z(4,0) was reported with its sign.

Statistical Analysis The SPSS statistical software package for Windows (version 10.1, SPSS, Inc.) was used for statistical analysis. Continuous-variable normality of all data samples was first confirmed by the Kolmogorov-Smirnov test. The Student t test for unpaired data was used for comparison between MICS and microphaco outcomes. Statistical analysis of differences in dichotomous variables between MICS and microphaco was performed by the chi-square test. All tests were 2 tailed, and acceptable significance was recorded when the P value was less than 0.05.

RESULTS Patients Fifty of 30 patients (18 women, 12 men) were enrolled in the study. The mean age of the patients was 68.4 years (range 45 to 87 years). The MICS group comprised 25 eyes of 16 patients and the microphaco group, 25 eyes of 18 patients. Table 1 shows the patients’ characteristics and Table 2, the surgical settings by group. The Acri.Smart 48S IOL was implanted in 37 eyes and the Acri.LISA 366D IOL, in 13 eyes. All

Patients (n) Eyes (n) Sex, n (%) Female Male Age (y) Mean G SD Range

MICS

Microphaco

16 25

18 25

11 (68.75) 5 (31.25)

9 (50.0) 9 (50.0)

67.8 G 10.8 45–87

69.1 G 7.49 53–80

MICS Z microincision cataract surgery

surgeries were uneventful. All patients were followed for 1 month postoperatively according to the study protocol. Incision Size The mean incision size was 1.73 mm G 0.08 (SD) (range 1.60 to 1.90 mm) in the MICS group and 2.24 G 0.05 mm (range 2.15 to 2.30 mm) in the microphaco group. The difference between groups was statistically significant (P!.001).

Table 2. Surgical parameters. Group Parameter Intended incision size (mm) Capsulorhexis diameter (mm) Phacoemulsification microtip (degrees) Phacoemulsification microtip caliber Prechopping Power (%) Aspiration flow (cm3/min) Vacuum (mm Hg) Anterior chamber pressure (cm3 H2O) Mode Irrigation/aspiration of the cortical remnants (mm Hg) Irrigation/aspiration of OVD (mm Hg)

MICS

Microphaco

1.4

2.2

5.5 30

5.5 30

0.9

0.9

Yes 20–30 25 550 90

Yes 20–30 25 550 90

Hyperpulse, 80 msec, 40% 450

Hyperpulse, 80 msec, 40% 450

40

40

MICS Z microincision cataract surgery; OVD Zophthalmic viscosurgical device

J CATARACT REFRACT SURG - VOL 35, MARCH 2009

470

MICROINCISION VERSUS MICROCOAXIAL PHACOEMULSIFICATION

Table 3. Comparison of postoperative visual acuity, refraction, slitlamp examination, and IOP between the groups. Group Parameter Mean UCVA* G SD 1 day 1 week 1 month Mean BSCVA* G SD 1 week 1 month Mean sphere (D) G SD 1 week 1 month Mean cylinder (D) G SD 1 week 1 month Mean IOP (mm Hg) G SD 1 day 1 week 1 month Mean flare (%) 1 day 1 week 1 month Mean edema (%) 1 day 1 week 1 month Mean Seidel (%) 1 day 1 week 1 month Mean PCO (%) 1 day 1 week 1 month

MICS

P Microphaco Value

0.29 G 0.20 0.51 G 0.26 0.54 G 0.23

0.33 G 0.19 .58 0.64 G 0.27 .09 0.71 G 0.27 .06

0.74 G 0.26 0.78 G 0.27

0.80 G 0.19 .42 0.86 G 0.20 .32

0.11 G 0.90 0.16 G 0.97

0.02 G 0.81 .60 0.15 G 0.96 .90

0.75 G 0.53 0.61 G 0.62

0.96 G 1.11 0.65 G 0.75

.40 .50

14.32 G 4.4 13.88 G 2.64 13.75 G 2.77

16.41 G 6.19 .19 14.09 G 3.72 .82 14.38 G 3.03 .43

56.0 16.0 0.0

30.4 4.2 0.0

.07 .17 d

44.0 12.0 0.0

87.0 4.2 0.0

.002 .32 d

8.0 0.0 0.0

0.0 0.0 0.0

.17 d d

4.0 4.0 4.0

8.7 4.2 0.0

.50 .98 .31

BSCVA Z best spectacle-corrected visual acuity; MICS Z microincision cataract surgery; PCO Z posterior capsule opacification; UCVA Z uncorrected visual acuity *Decimal conversion from Snellen

Visual Acuity, Refraction, and Biomicroscopy Table 3 shows the postoperative outcomes by group. At 1 day, the UCVA did not differ significantly between the MICS group and microphaco group. Differences in UCVA between the 2 groups were at the limit of statistical significance at 1 week (P Z .09) and at 1 month (0.54 G 0.23 versus 0.71 G 0.27) (P Z .06). However, there were no statistically significant differences between groups in BSCVA, sphere, or cylinder at any postoperative visit.

Figure 5. Postoperative OCT–measured CCT and mean thickness in a 2.0 to 5.0 mm area and 5.0 to 7.0 mm area of the cornea by group (CCT Z central corneal thickness; CT Z mean thickness; MICS Z microincision cataract surgery; P Z P value denoting the only significant difference).

The slitlamp biomicroscopic signs (ie, IOP and percentage of the eyes with flare, corneal edema, positive Seidel signs, and posterior capsule opacification) showed that MICS produced less corneal edema on the first postoperative day (44% versus 87%) (P Z .002) (Table 3). No eye in either group had anterior capsule opacification, IOL deposits, or abnormalities in IOL positioning or centration. Two eyes (8%) in the MICS group had a positive Seidel sign 1 day postoperatively. In both eyes, the leakage was minimal and was difficult to detect on OCT; neither patient had complaints, and both had normal IOP. The cases were managed with bandage contact lens. On follow-up, the leakage disappeared with favorable outcomes in both cases. Incision Imaging Three categories of OCT incision outcome parameters were differentiated: pachymetric (corneal thickness) values, qualitative (nonnumerical) incision data, and quantitative (numerical) incision data. The MICS group had statistically significantly less corneal thickness in an area of 5.0 to 7.0 mm than the microphaco group (659.92 G 56.74 mm versus 697.00 G 80.56 mm) (P Z .066), but only at 1 day (Figure 5). Table 4 shows the qualitative incision characteristics. The epithelial edge was not gaped in any case. At 1 month, all incisions in both groups were without epithelial or endothelial gaping, endothelial bulge, or Descemet detachment. Quantitative incision data (ie, incision angle and thickness) showed that corneal thickness 1.0 mm temporal to the incision was slightly less in the microphaco group than in the MICS group at 1 day 1 (0.95 G 0.14 mm versus 0.88 G 0.13 mm) (P Z .09). The angle of the incision, trigonometrically calculated by using OCT measurement parameters, is shown in Table 5 and Figure 6; there were no statistically significant differences between groups.

J CATARACT REFRACT SURG - VOL 35, MARCH 2009

471

MICROINCISION VERSUS MICROCOAXIAL PHACOEMULSIFICATION

Table 4. Postoperative incision data measured by OCT. Postoperative Exam 1 Day Parameter

MICS

1 Week

Microphaco P Value

Epithelial gaping (%) 0.00 0.00 Endothelial gaping (%) 64.00 72.00 DM detachment (%) 60.00 80.00 Endothelial bullae (%) 8.00 16.00 Mean % no coaptation G SD 3.12 G 7.61 2.65 G 5.48

d .54 .12 .39 .46

MICS

1 Month

Microphaco P Value MICS Microphaco P Value

0.00 0.00 76.00 72.7 32.00 45.5 12.00 9.1 1.10 G 2.51 0.59 G 1.22

.78 .34 .74 .82

0.00 0.00 0.0 0.00 0.00

0.00 0.00 0.00 0.00 0.00

d d d d d

DM Z Descemet membrane; MICS Z microincision cataract surgery

Topography and Aberrometry One month after surgery, corneal topography maps showed that the mean corneal power did not differ between the MICS group and microphaco group (44.12 G 2.26 D versus 43.96 G 1.76 D) (P Z .90). The mean corneal asphericity (Q) differed significantly between groups, with a better prolateness preservation in the MICS group than in the microphaco group (Q 4.5 mm: 0.08 G 0.39 versus 0.20 G 0.72, P Z .05; Q 8.0 mm: 0.22 G 0.45 versus 0.05 G 0.49, P Z .04). Figure 7 shows the corneal aberrations with the corresponding P values. The RMS values for astigmatism and HOA were slightly better in the MICS group than in the microphaco group (P Z .06 and P Z .05, respectively). The Strehl ratio did not differ significantly between the MICS group and the microphaco group (0.12 G 0.03 versus 0.12 G 0.05 (P Z .53). DISCUSSION The quality of the incision has a great influence on the outcomes of cataract surgery; the smaller the incision, the less trauma to the eye and thus the better the desired effect. However, minimizing the incision size is not enough to obtain the optimal outcomes. Small incisions that can control optical changes of the cornea and neutralize astigmatism, advanced surgical technology and IOLs, and surgeon experience are also needed to counteract aberrations. In this respect, small-incision clear corneal phacoemulsification is associated with more wound stability with a decrease in regular and irregular astigmatism6 and in corneal aberrations.7–11 In contrast, it has been suggested that the absence of a sleeve in bimanual phacoemulsification might put the wound under mechanical and thermal stresses. This could distort wound architecture through oar locking of instruments and thus yield inferior wound integrity compared with sleeved microincision coaxial phacoemulsification and/or even cause histomorphological

damage.8,20 These factors motivated us to perform the current study to evaluate, by an accurate objective method, the quality of the corneal incision used with the 2 methods of microincision IOL surgery currently available: MICS and microphaco. To fully understand how the incision behaves, we studied all parameters that indicate incision quality, including visual, refractive, biomicroscopic, topographic, and corneal aberrometric outcomes. Clinically, we did not observe any statistically significant differences between the MICS group and microphaco group except that the MICS group had a lower percentage of corneal edema on the first

Table 5. Postoperative OCT-measured incision thickness. Mean G SD Parameter

MICS Group

Microphaco Group

Central incision thickness (mm) 1 day 1.09 G 0.17 1.09 G 0.16 1 week 0.95 G 0.17 1.02 G 0.21 1 month 0.85 G 0.08 0.86 G 0.1 Incision thickness 1.0 mm nasal (mm) 1 day 0.89 G 0.12 0.93 G 0.12 1 week 0.81 G 0.07 0.82 G 0.11 1 month 0.80 G 0.08 0.76 G 0.07 Incision thickness 1.0 mm temporal (mm) 1 day 0.95 G 0.14 0.88 G 0.13 1 week 0.83 G 0.09 0.84 G 0.08 1 month 0.8 G 0.11 0.78 G 0.09 Incision angle (degrees) 1 day 42.05 G 13.23 39.25 G 9.89 1 week 45.71 G 16.04 42.50 G 16.67 1 month 46.49 G 8.98 44.24 G 10.57 MICS Z microincision cataract surgery

J CATARACT REFRACT SURG - VOL 35, MARCH 2009

P Value

.82 .16 .95

.27 .65 .11

.09 .67 .41 .4 .17 .37

472

MICROINCISION VERSUS MICROCOAXIAL PHACOEMULSIFICATION

Figure 6. Optical coherence tomography images showing (A) the angle of an MICS incision (white arrow), (B) the angle of a microphaco incision (white arrow), (C) a thick incision in an MICS case, and (D) a thin incision in a microphaco case (MICS Z microincision cataract surgery).

postoperative day. Our clinical observation was subsequently confirmed objectively by OCT pachymetric assessment, which showed lower corneal thickness values in a 5.0 to 7.0 mm area of the cornea in the MICS group, also at 1 day. This confirms the role of OCT as an accurate quantitative tool to assess incision effect and quality, as reported by Behrens et al.12 This effect disappeared gradually throughout the followup, and the 2 types of microincision surgeries behaved similarly. We studied all parameters of the incision using OCT. Because OCT is a noncontact method, any degree of incision deformity can be attributed to ocular dynamics without external forces applied to the wound. We also were able to detect subtle signs on OCT that were not detected at the slitlamp. These signed included spontaneous gaping in different areas of the incision that, in most cases, was clinically correlated with positive Seidel signs. We were also able to detect a degree of localized gaping of the internal aspect of the corneal wound that was associated with inward incision leakage as well as areas of localized Descemet membrane detachment or bulging and

Figure 7. Corneal aberrations with a 6.0 mm pupil diameter in both groups with corresponding P values (HOA Z higher-order aberration; MICS Z microincision cataract surgery; RMS Z root mean square).

sometimes bullae in the area of the wound that were not detected by slitlamp examination. Our findings agree with those in many other studies.12,21,22 The results were similar in the MICS group and microphaco group, with no statistically significant differences. Also, all incisions were anatomically perfect without gaping or abnormality at the end of the first postoperative month. Quantitative incision measurements using OCT showed that the microphaco group had slightly less corneal thickness 1.0 mm temporal to the incision at 1 day only; this may support the theory in a previous study.8 This was due to the sleeved phaco tip used in the microphaco group, although the effect was temporary. The angle of the incision data showed that incision quality was excellent in both groups. The angles of all incisions were in the range of the previously described23 critical angle to obtain secure ocular incisions (especially sutureless cataract incisions) that are unaffected by the IOP level and that provide a perfectly coapted barrier against invasion of pathogenic organisms. Although the observation of variable and sometimes poor wound apposition with fluctuation in IOP have been reported by many authors,21,23–25 we believe that our results are more solid and representative of actual wound behavior in the short term as well as the long term because our study was performed in vivo in human eyes with natural eye and incision dynamics. Other studies used postmortem globes of cadaver human and/or animal eyes or ex vivo models. Our study also had a larger number of cases and a longer follow-up period. Our results disagree with 1 study of corneal wound architecture and integrity after phacoemulsification.8 That is, the finding that microincision coaxial phacoemulsification and standard coaxial phacoemulsification induce less wound stress and alteration of wound morphology leading to wound leakage than MICS may only apply experimentally. This belief is augmented by the results of evaluating incision quality from a topographic and aberrometric viewpoint. Our results showed that MICS incisions maintain normal corneal asphericity and respects corneal prolateness more than microphaco incisions. Analysis of corneal aberration shows that astigmatism and HOA RMS were slightly, but not significantly, better in the MICS group. This agrees with results in our previous study,7 and we are in the process of comparing corneal optical quality between MICS and microphaco with the preliminary data supporting our results. Our results confirm an intersecting observation reported by others12 that a localized subclinical Descemet membrane detachment in the internal aspect of the incision could be a result of the corneal endothelial

J CATARACT REFRACT SURG - VOL 35, MARCH 2009

MICROINCISION VERSUS MICROCOAXIAL PHACOEMULSIFICATION

cell pump not functioning in the early postoperative period. This sign, seen in OCT images in the subsequent follow-ups, is associated with recovery of the pump and an improvement in corneal function. We also agree that wound stretching during IOL insertion and double-cut incisions may be additional risk factors for wound stress and detachment of Descemet membrane, which may cause wound gape and poor incision quality, especially with self-sealing clear corneal incisions. Our results, however, indicate that our method of IOL implantation with our wound-assisted injection technique, combined with the use of MICS IOLs and advanced instrumentation, had countered this effect, leading to good-quality incisions, even in eyes in which sleeveless-tip MICS was performed. Thus, in disagreement with the findings of others, our findings show that small incisions, and even microincisions, are self-sealing and perfectly coapted, as evidenced by the white line of the wound interface in the OCT images.12 To our knowledge, this is the first study of this type that compared incision quality in microincision coaxial and bimanual phacoemulsification conducted in living human eyes with a large number of cases and a relatively long follow-up period. In conclusion, both MICS and microcoaxial phacoemulsification provided good morphological incision quality, as shown by corneal OCT, and all incisions were optically neutral. The MICS incision respected corneal prolateness more and was associated with less corneal edema in the short term and less induction of corneal aberrations in the long term. Dynamically, the incisions of both techniques respected the cornea, with more or less similar in vivo behavior, taking advantage of the fact that minimizing the incision also minimizes tissue stress and improves incision quality. Finally, we found OCT to be a useful and helpful tool in assessing corneal incision quality in different types of cataract surgery. It allowed dynamic evaluation of incision behavior and its effect on the corneal tissue as a sensitive indicator of corneal function and incision quality. This noncontact device was able to accurately evaluate incision quality and detect mild signs that were not detectable by the slitlamp. REFERENCES 1. Kelman CD. Phaco-emulsification and aspiration; a new technique of cataract removal; a preliminary report. Am J Ophthalmol 1967; 64:23–35 2. Alio JL. What does MICS require? The transition to microincisional surgery. In: Alio JL, Rodriguez Prats JL, Galal A, eds, MICS: Micro-Incision Cataract Surgery. El Dorado, Republic of Panama, Highlights of Ophthalmology International, 2004; 1–4 3. Alio´ J, Rodrı´guez-Prats JL, Galal A, Ramzy M. Outcomes of microincision cataract surgery versus coaxial phacoemulsification. Ophthalmology 2005; 112:1997–2003

473

4. Alio´ JL, Klonowski P, Rodrı´guez-Prats JL, El Kady B. MICS (microincision cataract surgery). In: Garg A, Fine IH, Alio´ JL, Chang DF, Weinstock RJ, Mehta KR, Bovet JJ, Tsuneoka H, Malyugin B, Pinelli R, Pajic B, Mehta CK, eds, Mastering the Techniques of Advanced Phaco Surgery. New Delhi, India, Jaypee Brothers, 2008; 121–136 5. Tsuneoka H, Shiba T, Takahashi Y. Feasibility of ultrasound cataract surgery with a 1.4 mm incision. J Cataract Refract Surg 2001; 27:934–940 6. Osher RH, Injev VP. Thermal study of bare tips with various system parameters and incision sizes. J Cataract Refract Surg 2006; 32:867–872 7. Elkady B, Alio´ J, Ortiz D, Montalba´n R. Corneal aberrations after microincision cataract surgery. J Cataract Refract Surg 2008; 34:40–45 8. 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; 33:510–515 9. 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:S1079–S1082 10. Jiang Y, Le Q, Yang J, Lu Y. Changes in corneal astigmatism and high order aberrations after clear corneal tunnel phacoemulsification guided by corneal topography. J Refract Surg 2006; 22:S1083–S1088 11. Guirao A, Tejedor J, Artal P. Corneal aberrations before and after small-incision cataract surgery. Invest Ophthalmol Vis Sci 2004; 45:4312–4319. Available at: http://www.iovs.org/cgi/ reprint/45/12/4312. Accessed December 4, 2008 12. Behrens A, Stark WJ, Pratzer KA, McDonnell PJ. Dynamics of small-incision clear cornea wounds after phacoemulsification surgery using optical coherence tomography in the early postoperative period. J Refract Surg 2008; 24:46–49 13. Chee S-P, Bacsal K. Endophthalmitis after microincision cataract surgery. J Cataract Refract Surg 2005; 31:1834–1835 14. Herretes S, Stark WJ, Pirouzmanesh A, Reyes JMG, McDonnell PJ, Behrens A. Inflow of ocular surface fluid into the anterior chamber after phacoemulsification through sutureless corneal cataract wounds. Am J Ophthalmol 2005; 140:737–740 15. Taban M, Sarayba MA, Ignacio TS, Behrens A, McDonnell PJ. Ingress of India ink into the anterior chamber through sutureless clear corneal cataract wounds. Arch Ophthalmol 2005; 123:643–648 16. Haripriya A, Aravind S, Vadi K, Natchiar G. Bimanual microphaco for posterior polar cataracts. J Cataract Refract Surg 2006; 32:914–917 17. Chylack LT Jr, Wolfe JK, Singer DM, Leske MC, Bullimore MA, Bailey IL, Friend J, McCarthy D, Wu SY. The Lens Opacities Classification System III; the Longitudinal Study of Cataract Study Group. Arch Ophthalmol 1993; 111:831–836 18. World Medical Association Declaration of Helsinki. Ethical principles for medical research involving human subjects. Edinburgh, Scotland, 52nd general assembly, October 2000;. Available at: http://www.wma.net/e/policy/b3.htm. Accessed December 8, 2008 19. Radhakrishnan S, Rollins AM, Roth JE, Yazdanfar S, Westphal V, Bardenstein DS, Izatt JA. Real-time optical coherence tomography of the anterior segment at 1310 nm. Arch Ophthalmol 2001; 119:1179–1185 20. Kaid 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; 34:670–676

J CATARACT REFRACT SURG - VOL 35, MARCH 2009

474

MICROINCISION VERSUS MICROCOAXIAL PHACOEMULSIFICATION

21. McDonnell PJ, Taban M, Sarayba M, Rao B, Zhang J, Schiffman R, Chen Z. Dynamic morphology of clear corneal cataract incisions. Ophthalmology 2003; 110:2342–2348. Available at: http://chen.bli.uci.edu/publications/J50_Ophthalmology2003. pdf. Accessed December 8, 2008 22. Fine IH, Hoffman RS, Packer M. Profile of clear corneal cataract incisions demonstrated by ocular coherence tomography. J Cataract Refract Surg 2007; 33:94–97 23. Taban M, Rao B, Reznik J, Zhang J, Chen Z, McDonnell PJ. Dynamic morphology of sutureless cataract woundsdeffect of incision angle and location. Surv Ophthalmol 2004; 49(suppl 2):S62–S72 24. Khng C, Packer M, Fine IH, Hoffman RS, Moreira FB. Intraocular pressure during phacoemulsification. J Cataract Refract Surg 2006; 32:301–308

25. May W, Castro-Combs J, Camacho W, Wittmann P, Behrens A. Analysis of clear corneal incision integrity in an ex vivo model. J Cataract Refract Surg 2008; 34:1013–1018

J CATARACT REFRACT SURG - VOL 35, MARCH 2009

First author: Bassam Elkady, MD Vissum-Instituto Oftalmolo´gico de Alicante, Alicante, Spain