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Introduction: Pars plana vitrectomy (PPV) without endotamponade should not induce significant change to the refractive status of the eye. However, several studies have reported minor refractive changes after plain vitrectomy.
Purpose: To compare the changes in refraction following PPV and to examine the biometry parameters that may affect the refractive change.
Materials and methods: In this prospective cohort study, patients who were listed for 23-gauge 3-port PPV without buckling or silicone oil tamponade were enrolled between December 2015 and September 2017. Autorefraction, keratometry, anterior chamber depth (ACD), and axial length (AL) were measured preoperatively and three months postoperatively.
Results: This study involved 41 eyes from 38 patients. The mean spherical equivalent (SE) before PPV was -1.08 dioptres (D), (standard deviation (SD) 2.18), which changed to a mean of -1.88 D (SD 2.20) postoperatively. The mean SE change was -0.80 D (SD 1.61, 95% confidence interval (CI) -1.31 to 0.30 D, P = 0.003). The median astigmatism before PPV was 0.69 D (Interquartile range (IQR) 0.69 D) reduced to 0.66 D (IQR 0.60 D) after PPV (P = 0.882). Median ACD preoperatively was 3.55 mm (IQR 0.76 mm) and reduced postoperatively to 3.44 mm (IQR 0.67 mm), (P = 0.028). The median AL was 23.36 mm (IQR 1.42 mm) and 23.48 mm (IQR 1.56 mm) before and after PPV, respectively, (P = 0.029). No significant SE change was found between phakic and pseudophakic groups (P = 0.155).
Conclusion: Patients experience myopic shift post plain PPV, possibly due to the reduction of ACD. The ACD tended to be shorter in the pseudophakic group, suggesting that the myopic shift in the phakic group may be a result of the development of nuclear sclerosis cataract.