Controlled clinical trial comparing biaxial microincision with coaxial small incision for cataract surgery

Abstract

Purpose

Clinical outcomes of biaxial microincision versus coaxial small incision cataract surgery were compared in a prospective, controlled, paired-eye clinical study.

Methods

A total of 84 eyes of 42 patients underwent cataract surgery using the biaxial microincision (B-MICS) technique in either the right or left eye. The fellow eye was to undergo cataract surgery using the standard coaxial small incision (SICS) technique. All surgeries were performed using the Stellaris Vision Enhancement System and all eyes were implanted with an aspheric microincision intraocular lens (IOL). The 1.2-mm B-MICS incision was widened to 1.8 mm for IOL insertion. The main outcome measure was the change from baseline best-corrected visual acuity (BCVA). Secondary outcome measures were uncorrected visual acuity (UCVA), surgically induced astigmatism (SIA), manifest subjective refraction in spherical equivalent (MRSE), absolute phacoemulsification time (APT), effective phacoemulsification time (EPT), mean phacoemulsification power, and endothelial cell count (ECC). Follow-up was at 1 day, 3 days, 1 week, and 2 months.

Results

The treatment groups did not differ in baseline characteristics. Improvement in BCVA over baseline logarithm of the minimum angle of resolution (logMAR) was statistically significantly greater with B-MICS than SICS at 1 day (B-MICS −0.1, SICS −0.05; 95% CI −0.26 to −0.05, p=0.005). Mean improvement in UCVA from baseline was greater with B-MICS at 1 day (B-MICS −0.33, SICS −0.12; 95% CI −0.35 to −0.10, p=0.001), 3 days (B-MICS −0.39, SICS −0.26; 95% CI −0.22 to −0.02, p=0.022), 1 week (B-MICS −0.44, SICS −0.33; 95% CI −0.20 to −0.009, p=0.033), and 2 months (B-MICS −0.47, SICS 0.38; 95% CI −0.19 to +0.002, p =0.054). At 2 months, SIA was significantly lower with B-MICS than SICS (B-MICS 0.70 D, SICS 0.89 D; 95% CI −0.39 to −0.1, p=0.045), as was endothelial cell loss (B-MICS −1.4%, SICS −7.8%; p=0.05). The EPT was lower with B-MICS (B-MICS 1.60 s, SICS 2.80 s; 95% CI −1.68 to −0.77, p<0.001) with no difference in mean phaco power.

Conclusions

Compared to the standard small incision technique, B-MICS showed earlier improvement in BCVA, better overall UCVA, less SIA, and less endothelial cell loss.

Keywords

Biaxial microincision Cataract surgery Coaxial small incision

Introduction

Scientific background and explanation of rationale

The evolution in cataract surgery technology and surgical techniques continues to provide safer, faster, and better patient outcomes. Phacoemulsification, invented in the late 1960s, allowed the crystalline lens to be extracted through relatively small incisions. However, the potential benefit of small incision surgery was not fully realized until the development of foldable intraocular lenses (IOLs) in 1989 (1). A body of clinical evidence showed that smaller incision size was associated with fewer wound-related complications, less postoperative inflammation, much less surgically induced astigmatism (SIA) and other optical aberrations, faster visual recoveries, and better visual outcomes (2-5). Early phaco machines used continuous ultrasound energy, which generated heat and risked burns. The next evolution was pulsed ultrasound, with rapid on-off bursts of energy that cooled the tip while maintaining effective cutting. Pulsed ultrasound provided surgeons with better thermal control at the wound site and fewer corneal burns (6). Thermal control paved the way for microincision surgery using the bare, unsleeved, phaco needle. Removing the sleeve allowed incision sizes of 2 mm and less. Improvements in fluidics and control of high vacuum levels contributed to improved anterior chamber stability. Advances in IOL design produced IOLs that fit through microincisions. Surgical techniques kept pace with the evolving technology. Biaxial microincision phaco, first described by Shearing et al in 1985 (7), employs a 2-handed approach. Unlike conventional coaxial phaco, the bimanual technique employs 2 phaco handpieces, one for irrigation and one for emulsification and aspiration, with the tips inserted through 2 incisions in the cornea. Biaxial phacoemulsification has the potential to further reduce phacoemulsification energy, fluid leakage, and surgical trauma (8). The current study compares safety, speed of recovery, and surgical outcomes between biaxial microincision surgery (B-MICS) and coaxial small incision surgery (SICS) in study participants implanted with the same microincision IOL.

The null hypothesis was that no difference in speed of recovery of best-corrected visual acuity (BCVA) would be found between the B-MICS and SICS surgical techniques.

Patients and Methods

Trial design

This was a prospective, single-masked, controlled, paired-eye, clinical study. Patients who were scheduled to undergo bilateral cataract surgery with phacoemulsification cataract extraction were screened for eligibility.

Both eyes of participants were assigned with a 1:1 allocation to undergo cataract surgery using the B-MICS technique in the first eye and the SICS technique in the second eye.

The eye with the worse preoperative BCVA was selected as the first eye. If BCVA was the same in both eyes, the right eye was chosen to undergo surgery first. The second surgery was performed no later than 6 weeks after the first surgery. All eyes were implanted with the same IOL model (Akreos AO MI60 MICS, Bausch & Lomb Surgical, Aliso Viejo, CA, USA).

The study was approved by the Ethics Committee (EC) of the Medical Faculty of Ruhr University, Bochum, Germany, and conducted in accordance with the Declaration of Helsinki. The EC-approved informed consent form and patient information sheets were signed by each participant in the study. No changes in methods occurred after trial commencement.

Participants

Participants were enrolled from a series of consecutive patients who were scheduled to undergo bilateral phacoemulsification with IOL implantation for the treatment of cataract and who met the inclusion and exclusion criteria shown in Table I. In brief, participants had to be over age 18, have potential visual acuity ≥20/40 in both eyes, and bilateral cataract, but no ocular malformation, syndrome, disease, or impairment that might prevent full visual rehabilitation; no contact lens wear and no preoperative endothelial cell count <1000 cells/mm².

Table I

Inclusion and Exclusion Criteria

Inclusion criteria

Male or female 18 years or older

Meets local minimum age requirements for intraocular lens implantation following cataract surgery

Clear ocular media except for the presence of cataract

Potential visual acuity ≥20/40 in both eyes

Exclusion criteria

Ocular conditions that may prevent full visual rehabilitation after successful surgery

Rubella, or bilateral congenital, traumatic, or complicated cataract

Previous intraocular surgery, or ocular malformation or tumor in either eye

Anterior segment pathology in either eye; e.g., recurrent or ongoing iritis or uveitis, iridocyclitis, rubeosis iritis; clinically significant Fuchs dystrophy, clinically significant anterior membrane dystrophy, zonulolysis, defective zonules, pseudoexfoliation

Inflammation or edema of the cornea; e.g., keratitis, keratoconjuncti- vitis, keratouveitis, or clinically significant corneal dystrophy in either eye

Active anterior or posterior segment inflammation or infection

Uncontrolled glaucoma, optic atrophy, diabetic retinopathy in either eye

Macular degeneration (either wet or dry) in either eye

Clinically significant retinal pigment epithelial changes in either eye

Any disease which, in the opinion of the investigator, might interfere with the conduct of the study

Use of topical or systemic steroids or nonsteroidal inflammatory drugs

Contact lens wear

Preoperative corneal endothelial cell count of both eyes <1000 cells/mm²

Participation in an investigational study within the last 3 months

Inability to read

The study was conducted at the Institute of Vision Science, Ruhr University.

Interventions

Stop-and-chop phacoemulsification was performed on all eyes using the Stellaris Vision Enhancement System (Bausch & Lomb Surgical) by the same surgeon (H.B.D.) who has extensive experience with both B-MICS and SICS techniques. Biaxial microincision. For this technique, a corneal incision of about 1.2 mm in width and 1.5 mm in length was made at the 11 o'clock position, parallel to the limbus. A 1-mm incision was made at the 2 o'clock position for insertion of a 19-gauge irrigating chopper (Geuder, Heidelberg, Germany). The anterior chamber was filled with a viscoelastic (Healon, Abbott Medical Optics, Santa Ana, CA, USA). After continuous curvilinear capsulorhexis with a 24-gauge bent needle, hydrodissection and hydrodelineation were performed. Phacoemulsification was performed through the 11 o'clock incision.

Coaxial small incision. A 2.75-mm-wide clear corneal tunnel incision was created at the 12 o'clock position in a 2-step procedure. One-millimeter incisions were created at the 10 o'clock and 2 o'clock positions. The anterior chamber was filled with viscoelastic (Healon, Abbott Medical Optics), and capsulorhexis, hydrodissection, and hydrodelineation were performed as described for the B-MICS technique. In preparation for phacoemulsification, a 19-gauge phacoemulsification needle (Bausch & Lomb Surgical), with a sleeve and 2 side ports for irrigation, was inserted into the corneal tunnel incision. A manual chopper (Neuhann, Geuder) was inserted through the 2 o'clock side port.

The microincision IOL was implanted in all eyes using the Viscoject 1.8 single use inserter, LP604350 (Medicel, Wolfhalden, Switzerland). The incision was enlarged to 1.8 mm in the B-MICS group for wound-assisted lens insertion. There was no need for incision enlargement in the SICS group.

Outcomes

The primary outcome measure was the change from baseline BCVA. The BCVA was measured using the Optec 6500 vision testing device (Stereo Optical Co., Chicago, IL) and expressed in logarithm of the minimum angle of resolution (logMAR) at 4 postoperative time points. The change from baseline to each of the 4 time points was compared and the confidence interval (CI) of the adjusted difference between groups and p values were calculated. Secondary outcome measures included uncorrected visual acuity (UCVA) expressed in logMAR, surgically induced astigmatism (SIA) in diopters, and phacoemulsification (phaco) times. Absolute phacoemulsification time (APT) is the length of time, in seconds, that the ultrasound was used with the foot pedal in position 3. Effective phacoemulsification time (EPT) is the APT (seconds) times the mean phaco power (%) used during the surgery. Mean phaco power (MPP) is the average ultrasound power used during the surgical procedure, expressed in percent. Total surgical time, from first incision to wound hydration, was expressed in seconds. The balanced saline solution used during the procedure was collected in the cassette at the end of the surgical procedure, and measured in mL. Corneal endothelial cell counts in the central cornea were calculated using a noncontact specular microscope device (EAT Endothelial Analysis System, Rhine-Tec, Krefeld, Germany).

All postoperative measures were assessed at 4 visits: 1 day (1D), 3–4 days (3D), 7–10 days (1 week), and 7–9 weeks (8 weeks) after surgery except ECC, which was assessed at 1 week and 8 weeks. Safety evaluation included adverse event rates, slit-lamp examination, intraocular pressure (IOP), manifest subjective refraction, and concomitant treatment.

Surgically induced astigmatism was defined as the vector difference between the baseline and postoperative astigmatic correction vectors and was calculated as follows:

\sqrt{C y l 0^{2} + C y l^{2} - 2 \times C y l 0 \times C y l \times \cos (θ)}, where

Cyl0 = baseline cylinder,

Cyl = postoperative cylinder,

and θ = 2x (baseline cylindrical axis – postoperative cylindrical axis).

Anterior chamber inflammation was to be measured by laser cell flare meter and anterior chamber stability assessed by the investigator according to an evaluation scale.

Randomization and sequence generation

A computer was used to generate the allocation sequence. The surgeon received a set of 44 sealed envelopes containing the allocation sequence. For each patient enrolled, the appropriate envelope was opened the day before surgery. From this time point the investigator was no longer masked. The patient was masked for the study duration. The treatment used per eye was collected on the case report form (CRF). The on-site monitor gathered the allocation envelope for each patient and recorded the sequence number and group. The statisticians received a sealed envelope containing the computer allocation list, which was opened after a blinded review meeting defining major and minor deviations.

Statistical methods

Using a 2-sided paired t test with alpha = 0.05, and assuming a standard deviation of 0.20 and a correlation between contralaterally treated eyes of 0.5, a sample size of 35 contralaterally treated subjects yielded 80% power to detect a 1-line (0.10 logMAR) difference in BCVA between surgical procedures. Forty subjects (80 eyes) were planned to obtain 35 subjects (70 eyes) to complete the study.

Summaries for continuous variables included the sample size, mean, standard deviation, median, minimum, and maximum. Summaries for discrete variables included the tabulation of frequencies and percentages. Baseline values were defined as the last non-missing measure prior to surgery and IOL implantation.

The primary endpoint, the observed BCVA (measured in logMAR), and change from baseline was summarized by surgical procedure and visit using quantitative descriptive statistics. The 2 surgical procedures were compared using an analysis of variance for cross-over design (subject, sequence, surgical procedure, and operative order effects). The change from baseline to each of the 4 timepoints was compared and the confidence interval (CI) of the adjusted difference between groups and the p values were calculated. In the absence of baseline data, the 95% CI of the difference between groups were provided. Additionally, the proportion of eyes in each surgical procedure with a BCVA change (improvement) from baseline of at least 3 lines was summarized.

No additional analyses were made

Three analysis sets were defined. The safety set (SS) included all the eyes that had IOL implantation using the biaxial B-MICS microincision surgery or coaxial SICS small incision surgery. The full analysis set (FAS) includes all the eyes that underwent cataract surgery using either the B-MICS or SICS technique and at least one post-baseline value for main efficacy criterion. The per protocol set (PPS) includes all the eyes that underwent cataract surgery using either the B-MICS or SICS technique and had at least one post-baseline value and no major deviations at inclusion or during the study.

Results

Recruitment

Eligible participants were recruited from April to October 2008 and the study was completed in January 2009. Participants attended the clinic at enrollment through follow-up visits at 1 day, 3 days, 1 week, and 8 weeks, when the trial was completed as planned. There were no statistically significant preoperative differences between the 2 treatment groups.

Baseline data

Table II lists the demographics and baseline measures. No statistically significant between-group differences were found in keratometry, BCVA, manifest refraction, or endothelial cell count at the preoperative baseline. The cataract densities were similar for both techniques (Tab. III).

TAE II

Baseline Measures and Demographics

	All subjects
Mean age, y	72.1±10.3 (range 41-86)
Gender	58% (23/40) female, 42% (17/40) male
	B-MICS	SICS	p value
Keratometry: (K1+K2)/2	43.69±1.522	43.76±1.589	0.81
Best-corrected visual acuity (Log MAR)	0.27±0.180	0.24±0.183	0.69
Manifest refraction (D)	−0.07±2.825	0.18±2.329	0.36
Endothelial cell count (cells/mm²)	2196±377	2243±338	0.29

B-MICS = biaxial microincision surgery; SICS = coaxial small incision surgery.

Table III

Preoperative Classification of Cataract by Surgical Procedure

	B-MICS (n=40), n (%)	SICS (n=39), n (%)
Cataract type
Nuclear	3 (7.5)	3 (7.7)
Combination	37 (92.5)	36 (92.3)
Density
Slight (1+)	2 (5.0)	2 (5.1)
Moderate (2+)	27 (67.5)	28 (71.8)
Dense (3+)	11 (27.5)	9 (23.1)

B-MICS = biaxial microincision surgery; SICS = coaxial small incision surgery.

Numbers analyzed

A total of 84 eyes of 42 patients were assessed for eligibility. One patient (2 eyes) was discontinued from the study before the surgery due to exclusion criteria. The remaining 82 eyes of 41 patients were allocated to either B-MICS or SICS surgical technique. Of these, 80 eyes (41 patients) underwent cataract surgery. One patient declined to participate for his second eye. One patient had a capsular rupture on the first operated eye and was not implanted with the Akreos MICS IOL. Both eyes were discontinued from the study per protocol.

A total of 79 eyes (40 patients) were included in the FAS and 76 eyes (39 patients) were included in the PPS. No differences were identified between the FAS and PPS analysis, and outcomes are reported on the FAS population.

Outcomes and Estimation

Visual acuity

Table IV(top) shows the mean BCVA at baseline and the changes from mean baseline BCVA at all visits. At postoperative day 1, the change in mean BCVA was statistically significantly greater in the eyes that underwent B-MICS than those that underwent SICS (−1.1 vs −0.5; p=0.005; 95% CI −0.26 to −0.05), corresponding to a gain in acuity of 3 lines (15 letters or −0.3 logMAR) or greater in 20% of the B-MICS eyes and only 5.6% of the SICS eyes (p=0.005). For the subsequent visits, no significant between-group differences were identified in change in BCVA from baseline. Figure 1 displays the mean ± SD BCVA and Figure 2 the changes in mean BCVA from baseline.

Table IV

Visual Acuity and Change from Baseline (logMAR)

Mean ± SD (n)		B-MICS		SICS		p
Mean ± SD (n)		Change from baseline	Mean ± SD (n)	Change from baseline		p
Best-corrected VA
Baseline		0.27±0.18 (40)	0.16±0.16 (35)a	0.24±0.18 (39)	0.27± 0.25 (36)a	0.69
V1 = D 1		0.16±0.16 (35)	+1 line: −11±0.24 ≥3 lines: 20% (n=7)	0.42± 0.24 (36)	+0 lines: 0.05±0.26 ≥3 lines: 5.6% (n=2)	0.001
V2=D 3-4		0.08±0.16 (39)*	+2 lines: 0.18±0.24 ≥3 lines: 30.8%	0.11±0.18 (39)	+1 line: 0.03±0.20 ≥3 lines: 25.6%	0.26
V3=D 7-10		0.1±0.11 (40)	+2.5 lines: −0.26±0.2 ≥3 lines: 33.3%	0.03±0.17 (39)	+2 lines: −0.21±0.20 ≥3 lines: 35.9%	0.345a
V4 W = 7-9		0.02±0.1 (39)a	+3 lines: −0.28±0.18 ≥3 lines: 33.3%	0.01±0.1 (38)a	+2 lines: 0.23±0.14 ≥3 lines: 28.9%	0.266
Uncorrected
Baseline	0.64±0.25 (40)			0.56±0.28 (39)
V1 = D1	0.31±0.20 (35)		+3 lines: −0.33±0.32	0.42± 0.24 (36)	+1 line: 0.12±0.39
V2 = D 3-4	0.24 ±0.20 (39)		+4 lines: −0.39±0.30	0.30±0.23 (39)	+3 lines: −0.26±0.36
V3 = D 7-10	0.20±0.20 (40)		+4 lines: −0.44±0.30	0.23±0.22 (39)	+3 lines: −0.33±0.31
V4 = W 7-9	0.15 ±0.20 (39)		+5 lines: −0.47±0.30	0.5±0.20 (38)	+4 lines: −0.38±0.30

B-MICS = biaxial microincision surgery; D = day; SICS = coaxial small incision surgery; V = visit; VA = visual acuity.

When n<40 (B-MICS) or <39 (SICS), only the applicable subset was used to measure change from baseline.

Fig. 1

Mean best-corrected visual acuity (BCVA) ± standard deviation shown for biaxial and coaxial techniques in logMAR.

Fig. 2

Changes in mean best-corrected visual acuity (BCVA) from baseline shown for biaxial and coaxial techniques in logMAR.

Table IV(bottom) shows the mean UCVA and changes in mean UCVA from baseline for all visits. Except for the 8-week follow-up, the B-MICS technique provided statistically significant improvements in UCVA compared to the SICS technique. Figure 3 and 4 summarize the results for UCVA and UCVA change from baseline.

Fig. 3

Mean uncorrected visual acuity (UCVA) ± standard deviation shown for biaxial and coaxial techniques in logMAR.

Fig. 4

Changes in mean uncorrected visual acuity (UCVA) from baseline shown for biaxial and coaxial techniques in logMAR.

Surgically induced astigmatism

One day after surgery, SIA was 1.05 D for B-MICS-treated eyes and 1.49 D for SICS-treated eyes (p=0.122; 95% CI −0.40 to 0.09). At the day 3 visit, SIA was 0.97 D and 1.06 D, respectively (p=0.49; 95% CI −0.37 to 0.17). At the week 1 and week 8 visits, SIA was statistically significantly lower in B-MICS than SICS eyes. At week 1, mean SIA was 0.63±0.388 D (B-MICS) and 1.05±0.847 D (SICS) (p=0.01; 95% CI −0.72 to −0.10). At the week 8 visit, mean SIA was 0.70±0.377 D (B-MICS) and 0.89±0.559 D (SICS) (p=0.045; 95% CI −0.39 to −0.10). Figure 5 displays the SIA comparison for the B-MICS- and SICS-treated eyes.

Fig. 5

Baseline astigmatism and postoperative surgically induced astigmatism (SIA) in the biaxial and coaxial groups, in diopters.

Manifest refraction spherical equivalent

Preoperatively, mean MRSE was −0.07 D for the B-MICS group of eyes vs +0.18 for the SICS group (p=0.36). At 1 day after surgery (V1), mean MRSE was statistically significantly lower for the B-MICS group than the SICS group (−0.08 D vs −0.38 D, p=0.02). Mean MRSE was not statistically different between the B-MICS and SICS groups at subsequent visits (3 days, −0.20 vs −0.10, p=0.47; 1 week, 0.33 vs −0.31, p=0.80; 8 weeks, −0.33 vs −0.31, p=0.80). Figure 6 summarizes the MRSE results.

Fig. 6

Manifest refraction spherical equivalent (MRSE) in the biaxial and coaxial groups, in diopters, at baseline and follow-up visits.

Surgical parameters

The APT and EPT were statistically significantly lower following B-MICS than SICS (APT 10.97 vs 14.70 seconds, p≤0.0001 and EPT 1.60 vs 2.80 seconds, p≤0.0001). Mean phacoemulsification power was 26.3% for B-MICS vs 27.3% for SICS (p=0.321). The quantity of fluid collected in the cassette was statistically significantly less in the B-MICS group than the SICS group (61.6 mL vs 66.4 mL, p=0.047). Total surgical time from first incision to wound hydration was less following B-MICS than SICS (7.78 vs 7.00 minutes, p=0.0005). Figure 7 and 8 summarize the changes in APT and EPT.

Fig. 7

Absolute phacoemulsification time (APT) in the biaxial and coaxial groups.

Fig. 8

Effective phacoemulsification time (EPT) in the biaxial and coaxial groups.

Endothelial cell loss

The mean endothelial cell density for the 40 eyes in the B-MICS group was 2196±377 cells/mm² preoperatively and remained stable (2207±375 cells/mm²) at the 1-week visit. Mean endothelial cell density for the 39 eyes in the SICS group before cataract surgery was 2243±338 cells/mm² and decreased to 2071±358 cells/mm² at 1 week. The endothelial cell density change from baseline was statistically significantly lower with B-MICS (11±464 cells/mm²) than with CICS (172±427 cells/mm²) at 1 week (p=0.034; 95% CI 14.31 to 346.42).

At 8 weeks, the mean endothelial cell density for the 40 eyes in the B-MICS group decreased from 2217±358 cells/mm² preoperatively to 2185±344 cells/mm². The mean endothelial cell density for the 39 eyes in the SICS group was 2261±324 cells/mm² preoperatively and decreased to 2083±276 cells/mm² at 8 weeks. The change from baseline with B-MICS was −31±480 cells/mm² and was −177±442 cells/mm² with SICS (p=0.053; 95% CI −2.14 to 292.39). Figure 9 displays the endothelial cell changes in the 2 groups of eyes over the course of the study.

Fig. 9

Endothelial cell counts, measured in cells per mm², at the first and last postoperative follow-up visits in the biaxial and coaxial groups.

Ancillary analyses

No post hoc or subgroup analyses were performed.

Complications

One subject had a posterior capsular rupture with anterior vitrectomy before lens implantation of his left eye and this eye was not included in the analyses. One subject had a severe decrease in IOP in his right eye after undergoing B-MICS. This subject fully recovered and the eye was included in the analysis. No other hypotony occurred. No leaks were identified in the corneal incisions, and no zonulolysis or vitreous prolapse, postoperative fibrin formation, or wound dehiscence occurred.

Discussion

Key findings

This study shows that both the B-MICS and the SICS phacoemulsification techniques have excellent surgical outcomes. With biaxial microincision, BCVA was statistically significantly better than SICS at day 1 and EPT was significantly shorter, with no statistically significant differences in astigmatism, or endothelial cell count relative to the coaxial small-incision technique.

Strengths and limitations

One of the study strengths is that this was a single surgeon study; therefore, there are no variations among surgeons with different skill and comfort levels in using the biaxial microincision and coaxial small incision techniques and no differences in phacoemulsification machines or surgical settings to take into account. It is a well-designed trial that is of clinical relevance and importance as cataract surgery continues to evolve into cataract-refractive surgery. A drawback with this study design is that subtle, unconscious differences in the surgeon's 2 techniques may not have been identified and analyzed.

Possible mechanisms

Surgical skill assures that visually disabling complications are minimized for a good visual outcome. Equivalent phacoemulsification time is a measure of the amount of energy the eye receives and is an indicator of the potential trauma the eye may undergo as a result. The lower EPT in the B-MICS group of eyes may contribute to faster healing and the microincision, itself, may heal faster than the small incision.

Comparison

Visual acuity. At 1 day after surgery the BCVA change from baseline for the B-MICS eyes was statistically significantly better than the SICS eyes, but did not reach significance at subsequent visits. This finding may indicate a possible faster visual recovery for the B-MICS technique. Uncorrected visual acuity in the B-MICS group of eyes was statistically significantly improved at all visits (except for the week 8 visit when p was of marginal significance at 0.055). The difference in very early UCVA results may also have been influenced by biometric error (0.3 D difference) rather than by surgical technique.

Our visual acuity results, compared with other studies of biaxial microincision B-MICS and conventional coaxial CICS phacoemulsification techniques, achieved statistical significance at several time points. In a similar study, the BCVA data were similar, but most of the other studies showed trending in this direction but not p<0.05.

Kurz et al (9) studied 70 eyes of 70 subjects using B-MICS with <1.5-mm incision and SICS with a 2.75-mm incision and BCVA as the main outcome measure. The BCVA with B-MICS was statistically significantly better than the coaxial control at 1 day, 3 days, and 8 weeks after surgery. In a later study of 94 complicated cases, Kurz et al (10) looked at both techniques and 1.5-mm (B-MICS) and 2.8-mm (SICS) incisions and found no statistically significant differences in corrected distance visual acuity at the 8-week follow-up (19).

Alió et al (11) conducted a 50-patient, 100-eye, prospective randomized study comparing outcomes of B-MICS with a 1.7-mm incision to SICS with a 3.1-mm incision and 3-month follow-up (11). While more favorable BCVA results were seen at 1 day using B-MICS, it did not rise to statistical significance at this or the 1- and 3-month follow-up visits. One difference between their study and ours is that Alió et al (11) analyzed actual acuity rather than change from baseline and this may have contributed to the difference in results.

Elkady et al (12) compared biaxial MICS (1.7-mm incision; 25 eyes of 16 patients) and coaxial MICS (2.2-mm incision; 25 eyes of 18 patients). The BCVA and UCVA results approached but did not achieve statistical significance at 1 week (p=0.09) and 1 month (p=0.06) with biaxial MICS surgery (12).

Crema et al (13) found no statistically significant differences in BCVA at 24 hours or at 1 year postoperatively in 60 eyes of 30 patients (13).

In a non B-MICS vs SICS study, Wang et al (14) compared 2.2-, 2.6-, and 3.0-mm microincisions using coaxial MICS techniques in 129 eyes of 83 patients. The data at 30 and 90 days after surgery showed a trend of improved UCVA with decreasing incision size but this was not statistically significant.

Surgically induced astigmatism. Reduction in SIA may be a significant achievement of MICS. In our study, significantly less SIA was seen in the B-MICS group at 1 and 8 weeks than with the SICS technique. The SIA at day 1 and 3 may have been affected by wound hydration variability and, therefore, this comparison is of limited value. Many studies have evaluated SIA relative to incision size over the years, from the relatively large incisions of the late 1990s to the microincisions available today (15). For the most part, the results of the recent studies on corneal changes with microincisions parallel ours. In their 50-patient study of 1.7–mm B-MICS and 3.1–mm coaxial incisions, Alió et al (11) calculated SIA by vector analysis (11). A mean vectorial astigmatic change of 0.36±0.23 D was induced in the B-MICS group and 1.2±0.74 D in the coaxial group (p<0.001).

Yao et al (16) compared corneal astigmatism in coaxial MICS (C-MICS; 1.7 mm) to SICS (3.2 mm) in 60 eyes (16). At 30 days after surgery, a statistically significant difference (p=0.001) was found between the mean postoperative ΔSim K value for the C-MICS and small incision group. The ΔSim K value is the change in simulated keratotomy, the difference in power between the steep and flat meridians. The ΔSim K value equaled 0.78±0.38 D in the C-MICS group compared with 1.29±0.68 D for the small incision group. In the previously cited study by Wang et al (14), SIA was statistically significantly greater with the 3.0-mm incision than the 2.6-mm and 2.2-mm incisions (p≤0.015) but the difference in SIA between the 2.6- and 2.2-mm incisions did not reach statistical significance at the 30- and 90-day follow-ups (14).

In a study of 120 eyes (60 patients and 60 eyes per group), Hayashi et al. (17) compared SIA in C-MICS with a 2.00-mm incision to the coaxial technique with a 2.65-mm incision using vector analysis. The mean induced corneal astigmatism was significantly less in C-MICS eyes than in coaxial eyes at 1 week and remained this way until the last measurement at 8 weeks postoperatively (p<0.05).

Elkady et al (12) measured corneal topography of patients before and after 2.0-mm incision surgery. Corneal astigmatism was not statistically significantly changed at 1 month and 3 months postsurgery from the preoperative baseline. Tong et al (18) measured anterior corneal topography in 36 eyes having B-MICS (1.5 mm) and standard coaxial cataract surgery (3.0 mm). The coaxial procedure induced greater changes in oblique astigmatism (p=0.0001), oblique trefoil (p=0.0035), vertical tetrafoil (p=0.002), total root mean square (RMS; p=0.007), and higher-order RMS (p=0.023) of corneal wavefront aberrations.

Morcillo-Laiz et al (19) found no statistically significant difference in SIA between B-MICS (1.5-mm incision) and standard SICS (2.8-mm incision) in 94 eyes of 64 patients using corneal topography and arithmetic, polar, and vector analysis (19). In the Kurz et al study (10), corneal astigmatism measured by corneal topography did not significantly change from the preoperative baseline in either the B-MICS or coaxial groups.

Endothelial cell loss. Endothelial cell loss with cataract surgery is multifactorial. Surgical trauma (20), shorter axial length eyes and longer phacoemulsification times (21), pupil size and IOL type (22), and increased nuclear color and opalescence (23) are among the factors associated with a greater risk of endothelial cell loss. A physiologic endothelial cell loss occurs with aging and this rate is significantly higher after phacoemulsification (20, 24, 25).

Mencucci et al (26), Kurz et al (9), and Alió et al (11) found no difference in endothelial cell loss between MICS and coaxial techniques. Alió et al (11) stated that endothelial cell loss is related to the amount of fluid circulating in the anterior chamber and that further progress should be made in fluidics control and in decreasing incision leakage to reduce the volume of fluid used in MICS surgery.

We looked at endothelial cell loss in other studies not directly comparable to ours and evaluated endothelial cell loss as a function of fluid used, final wound size, and phaco energy (22, 26-29). We noted no significant difference in endothelial cell loss in studies with less fluid use; however, the studies are not directly comparable due to different primary endpoints and confounding factors, such as a significant enlargement of the microincision to implant the IOL.

Surgical parameters. Phaco power, measured as EPT and APT, provides insight into energy use and its potential for trauma to the eye. The volume of irrigation fluid circulating through the eye can provide another indication of trauma, as excessive irrigation fluid can cause increased turbulence. Total surgical time gives surgeons a practical tool in providing care to patients (e.g., scheduling surgeries).

Mean EPT was statistically significantly lower for B-MICS in the Kurz et al (10) (2 vs 5 s, p=0.013) and Alió et al (11) (2.19 vs 9.2 s, p=0.001) studies, as was the EPT in the current study (1.6 vs 2.8 s, p≤0.0001). However, the amount of fluid used for surgery was less with B-MICS in our study (61.6 mL vs 66.4 mL, p=0.047) than in Alió et al's study (92.77 vs 113.84 mL, p=0.198). The lower turbulence associated with less fluid may contribute to lower endothelial cell loss.

In the Kurz et al study (10), the EPT was less than 3 seconds in 66% of eyes in the B-MICS group, compared with only 32% of eyes in the coaxial group. In Alió et al's study (11), B-MICS had a significant decrease in mean total phaco time (p<0.001) and mean EPT (p<0.001).

Cavallini et al (27) compared B-MICS with incision opened to 2.82 mm to standard coaxial surgery (2.63-mm incision). The B-MICS method used less balanced salt solution (114.51 vs 147.42 mL, p=0.004) and had a shorter total surgical time (p=0.045), but no difference in EPT. The surgeon was less experienced with B-MICS, another confounding factor.

In Kahraman et al (30), 66 eyes of 33 subjects were randomly assigned 1:1 to either B-MICS or standard coaxial (3.2-mm incision). Mean ultrasound time and mean surgical time were statistically significantly lower for the B-MICS group (p=0.001 and p=0.004, respectively); however, in a separate report by Crema et al (13), the eyes in the SICS group had significantly lower total ultrasound time than the MICS group (p=0.0001). Mencucci et al (26) compared B-MICS (40 eyes <2-mm incision opened to 3.2 mm for lens insertion) and standard coaxial surgery (40 eyes 3.2-mm incision) and observed no differences in surgical parameters.

These show that the B-MICS technique can significantly reduce surgical time, surgical energy, the amount of fluid used, and possibly trauma to eye, enabling faster recoveries.

In Hayashi et al's 2009 study of B-MICS (2.2-mm incision) and coaxial surgery (2.8 mm), mean ultrasound time was significantly lower in the coaxial group, while the volume of fluid and the endothelial cell loss measured up to 8 weeks later was not significantly different (17). Kahraman et al (30), who looked at B-MICS (wounds opened to 3.2 mm) and standard surgery (3.2 mm), reported statistically significantly lower mean ultrasound time with B-MICS (p=0.001) and no significant differences in volume of fluid used and endothelial cell counts, although B-MICS eyes had a greater loss of endothelial cells than standard surgery eyes. Dosso et al (28) compared C-MICS (1.8 mm) to coaxial surgery (2.8 mm) and reported no statistically significant differences between the techniques in ultrasound time, fluid use, and endothelial cell counts. Wilczynski et al's report of B-MICS (1.7-mm incision) compared to C-MICS (1.8-mm incision) showed significantly less volume of fluid use (p≤0.05) and higher EPT in the B-MICS group (p≤0.01) and no difference in endothelial cell loss (29). Mencucci et al (31) compared B-MICS (wound opened to 2.75 mm) to standard cataract surgery. Mean EPT, volume of fluid used, and endothelial cell loss were not statistically significant. Based on the above analysis between our study and others, we speculate that the lower endothelial cell loss seen in our study may be due to a combination of the microincision, less phaco energy, and less fluid circulation.

Limitations

This was an unmasked study with a single surgeon in relatively few eyes, about the same number as similar trials. The sample size was chosen to have 80% power to detect a 1-line (0.10 logMAR) difference in BCVA between surgical procedures.

Generalizability

The results from this study show a significant improvement in BCVA at 1 day after surgery and in UCVA at all but the last visit. Improvements in UCVA are expected with the removal of the cataract and implantation of the IOL. Improvements in BCVA support the assertion that B-MICS causes less trauma to the eye than SICS. Larger, multicenter, and multiequipment studies should be carried out to determine the rehabilitation of the eye after phacoemulsification and IOL implantation through microincisions.

Interpretation

Biaxial microincision surgery is a viable option for cataract surgeons who are concerned about reducing SIA. The biaxial technique allows for microincisions in the cornea and implantation of a microincision IOL for less trauma and more effective visual recovery.

Excellent results were achieved with both B-MICS and small incision cataract surgery. In the B-MICS technique, we observed better visual outcomes including initial BCVA, better UCVA, and lower SIA. Mean APT and EPT were lower, less fluid was used, and overall surgery time was lower. A smaller incision size, lower phaco energy, and less fluid circulation may also have contributed to lower observed endothelial cell loss. Use of B-MICS has the potential to play a key role in the evolution of cataract surgical techniques and technologies for safer, faster, and better outcomes.

Footnotes

ACKNOWLEDGEMENTS

The author thanks Lanie M. Adamson, MS, for critical edits of the author's manuscript.

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