Abstract
Purpose: :
Small gauge vitrectomy probes have smaller spheres of influence around the probe port allowing surgeons to dissect tissue close to the retina with reduced effects on mobile retinal tissue. A laboratory study was conducted to simulate the tissue membrane attraction under different flow conditions for vitrectomy probes in three gauge sizes.
Methods: :
A vertical thin wire of 0.003" in diameter was fixed to the bottom of an open-sky transparent container filled with balanced salt solution, forming a cantilever beam of one inch in effective length. A small rectangular piece of latex membrane simulating a tissue membrane was attached to the top of the wire at a right angle. The port of a vitrectomy probe was placed at various distances from the membrane. With cutting off, the vacuum pressure was increased until the membrane was attracted into the probe port. A high speed video camera with 10x lens was used to monitor and to capture the motion of the membrane. The aspiration flow rate was measured with an ultrasound flow meter. The attraction distance, the vacuum pressure, and the flow rate were recorded for six samples each of three gauge sizes (20G, 23G, and 25G).
Results: :
For any given distance, the 25G probes needed the largest vacuum pressure, and the 20G probes needed the least to attract the membrane into the port. At a distance of 0.34 mm the vacuum pressures were 116, 248, and 430 mmHg for 20G, 23G, and 25G probes, respectively. The 25G and 23G probes at 650 mmHg vacuums attracted the membrane 0.4 mm and 0.5 mm away from the port, respectively, while the 20G probes at 400 mmHg vacuum attracted the same membrane 0.6 mm away. However, at a given distance, the smaller gauge probes actually needed much smaller aspiration flow to attract the membrane, compared to the large gauge probe. At 0.27 mm distance, the volumetric aspiration flow rates were 11.7, 8.0, and 7.4 mL/min for 20G, 23G, and 25G probes, respectively.
Conclusions: :
Laboratory study indicates that the large gauge probe attracted the membrane into the probe port farther away than the smaller gauge probes at the same vacuum level. The 25G probe has a smaller sphere of influence and is more efficient in flow management in attracting tissue than the 20G probe.
Keywords: vitreoretinal surgery • retina