Purpose: To study the patterns of vitreous incarceration at sclerotomy sites by\udultrasound biomicroscopy (UBM) in patients subjected to valved or nonvalved small\udgauge pars plana vitrectomy.\udMethods: A prospective, comparative study of 88 eyes affected by epiretinal\udmembrane and macular hole. Patients were divided into four groups: valved or\udnonvalved 23-gauge (16 eyes each) and valved or nonvalved 25-gauge (20 eyes\udeach); their vitreal disposition was compared via UBM. Vitreal disposition was also\udassessed in 16 eyes of 16 patients subjected to valved 27-gauge pars plana\udvitrectomy.\udResults: Three vitreal patterns were identified: P0 (vitreous not visible or vitreous\udstrand distant from sclerotomy site), P1 (vitreous strand parallel to and in contact with\udsclerotomy site), and P2 (vitreous strand entrapped in sclerotomy site).The effect of\udvalved trocar use on vitreous incarceration appeared to be somewhat beneficial, but no\udstatistically significant effect could be shown (OR: 0.85, 95% CI 0.42 - 1.74, p=0.657).\udSimilarly, no differences in vitreous incarceration were shown among vitrectomy gauge\ud(23, 25, or 27) both in a model including valved trocars only (p=0.858) and in a model\udwith all available data (p=0.935). \udConclusions: In 23- and 25-gauge macular surgery, postoperative vitreous\udincarceration does not seem to be reduced by the use of valved cannulas and was\udsimilar to that observed in 27-gauge surgery.
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