ANALYSIS OF POSTOPERATIVE VISUAL OUTCOMES IN SMALL INCISION CATARACT SURGERY USING LINEAR AND FROWN INCISIONS: A SYSTEMATIC LITERATURE REVIEW

Introduction: Small incision cataract surgery (SICS) is a cost-effective and technically simple technique suitable for the resource-limited health care system. Theoretically there are different benefits of linear (straight corneal/scleral tunnel) and frown (curved, inverted U-shaped). Comparative outcome data are still not consistent across the literature and there is not yet enough evidence to determine whether there is a better incision configuration to optimize outcome. 
Methods: Systematic review with comprehensive search as per PRISMA 2020 guidelines. We searched five international databases (PubMed, Scopus, Web of Science, ScienceDirect, Google Scholar) for studies that compared postoperative visual outcomes for linear versus frown incisions. Twelve studies were included. Random-effects meta-analyses were used to estimate pooled proportions and mean differences with associated 95% CIs. Design-specific tools were used in quality appraisal and the evidence certainty was assessed using GRADE methodology. Qualitative results were integrated into the PAGER framework. 
Results: 64.3% of patients with a frown incision had best corrected visual acuity of ≥6/12, compared to 61.2% of patients with linear incision . The induced astigmatism (+0.13 diopters, and the number of eyes that reached ≥1.0 diopters of astigmatism (41.2% versus 37.3%) were significantly larger with linear incisions. Incision size significantly affected the results and smaller incisions of ≤7.5 mm had the best results of ≥6/12 compared to larger incisions of >7.0 mm. The role of uncorrected refractive error remained as the major limiting factor, with 27-30% difference in corrected and uncorrected visual acuity in both types of incisions.
Conclusions: There is evidence supporting the functional equivalence of the linear and frown incision configurations with regard to outcome determinants, and the size of the incision is shown to be a much more significant determinant of the outcome. They both have similar visual results, while the choice of the incision should be based on the surgeon's experience and local circumstances. The key is the optimization of refractive management during the postoperative period to achieve better visual outcome.