This analysis of five years of data from 11 studies found no significant differences between the techniques in CDVA, mean percentage of endothelial cell loss, laser flare photometry value, CCT change, or intraoperative and postoperative complications. However, effective phaco time was statistically significantly shorter and mean phaco power significantly lower in the biaxial group. Also, biaxial MICS cause less surgically-induced astigmatism (SIA). Based on these findings, the authors believe the biaxial technique to be more effective.
They reviewed data from 11 randomized controlled trials published between 2005 and 2010 and involving a total of 1,064 eyes.
Eight studies reported data for mean phaco power during cataract surgery. Mean phaco power was lower in the coaxial group in one study, not significantly different between the groups in one study, and lower in the biaxial group in the remaining six studies. Analysis found the between-group differences in phaco power to be statistically significant (P=0.005).
Seven studies reported data for mean effective phacoemulsification time (EPT). The mean EPT was shorter in the biaxial group than in the coaxial group in six of these studies. Analysis found the between-group differences in mean EPT to be statistically significant (P=0.0008).
The authors note that the biaxial technique seems to be associated with an earlier improvement in CDVA compared with the coaxial procedure. One study found that although there was no significant between-group difference in mean CDVA at 90 days or in the mean increase in CDVA, the mean visual rehabilitation rate (recovery time to reach best CDVA) was significantly shorter in the biaxial group than in the coaxial group (25.1 days versus 40.9 days; P=0.04). Another study observed no change in mean CDVA three hours following biaxial MICS but a significant deterioration of mean CDVA three hours after coaxial phacoemulsification.
They also note that six of the 11 studies compared the SIA in the two groups by vector analysis. However, the results were inconsistent. Although two studies suggested that a great advantage of MICS was that the microincisions did not produce an increase in astigmatism, two other studies reported no significant between-group difference in the amount of SIA. The different findings in these studies may be related to the differences in study design (different number, length, or localization of incisions).
The authors point to several limitations of this meta-analysis. They did not search for unpublished studies or original data; also, some trials lacked adequate allocation concealment, blinding, and sample-size assessment, which may leave them vulnerable to bias; also, not every study used the same phaco machine; and finally, a high level of between-studies variability was detected in some outcome measures. Hence, these results should be interpreted with caution.