Comparing the Efficiency of Valved Trocar Cannulas for Pars Plana Vitrectomy

Purpose: To compare the efficiency of different manufacturers' valved cannulas (23G, 25G and 27G) (Alcon, Bausch & Lomb, BVI, DORC, Optikon) in maintaining intraocular pressure during vitrectomy by measuring leak pressure and the difference between set and actual intraocular pressure, under BSS and air infusion. Methods: A BSS-filled reservoir was connected to a model eye allowing placement of leak-proof valved cannulas. A pressure sensor was interposed and the bottle height increased until leakage occurred. Air leakage was measured by connecting an air pump to different manufacturers' valved cannulas, inserted upside down to blow air against the valve with inside-out direction and immersed in soapy water to detect air bubbling. Results: The average BSS leaking pressure was 7.69 +/- 0.77 mmHg for 23G, 9.92 +/- 0.57 mmHg for 25G and 7.57 +/- 0.80 mmHg for 27G. The 25G valved cannulas opened at higher pressure (p < 0.05). The difference between set and actual pressure in BSS never exceeded 4 mmHg. Leakage pressure under air ranged between 10 and 55 mmHg. The 27G valves opened at an average 47.2 +/- 3.9 mmHg vs. 29.4 +/- 7.2 for 25G and 24.1 +/- 16.5 for 23G (27G vs. other gauges p < 0.05). The difference between set and actual pressure under air infusion never exceeded 2 mmHg. Conclusion: Despite significant differences, all tested valved cannulas satisfy safety criteria by keeping a surgically negligible difference between the set and actual intraocular pressure. The minimal leakage measure may act as a safety pressure damper under critical conditions.