The EVRS RD study, analyzed by the French National Institute of Statistics, demonstrated that vitrectomy performed with a Venturi pump machine almost triples the failure rate compared to the use a flow-control pump, independently of the surgeon’s experience, age and nationality. Let’s try to explain why.

Since a Venturi pump does not allow to control the quantity of liquid entering the hand piece, a low cutting speed cannot be used otherwise the risk of browsing the retina is too high (if 600 cuts per minute had been selected). To decrease the dangerousness of the hand piece a high speed cutting is mandatory but this is at the expense of a limitation of both performance and effectiveness. For example, as it has been established that removing the posterior hyaloid is statistically linked to a lower failure rate, one can want to do so in a case where the vitreous cortex is adherent to the retina. If the cutting rate has been set up at 4000 per minute, the retina does not move because the adherent vitreous does not come, and this can be illustrated: a curve needle passing very close to the retina can catch all the adherent vitreous that has not been removed during the high speed cutting. To remove the hyaloid, one has to achieve a peeling maneuver.

The vitreous is a non newtonian fluid; it is the BSS that carries on the vitreous fibers into the cutter’s port. With high speed cutting the vitreous cortex itself does not have the time to enter in between two cuts and a shaving maneuver is performed, allowing PVR to develop post operatively, while the cortex peeling dissection does prevent it.

At the periphery, a peeling cannot be performed, but the issue is just the same. If time is not given for the vitreous to be attracted into the port, then a thick mattress of collagen will remain at the vitreous base. As the vitreous does not come one can think to enter in the vitreous base but one ends up with a raw.

To achieve a more complete job, time must be allowed to the adherent vitreous to move towards the port but then the retina will follow. To avoid catching the retina, one must use a low and precise aspiration flow between 1 to 3 cc per minute, lower than the natural outflow of BSS induced by the infusion pressure. To obtain such a low flow, the flow control pump acts like a dam that reduces the flow of a river while creating a positive upstream pressure. I

Such a precise dissection cannot be achieved by a Venturi pump, which performance is limited to generating a negative pressure, increasing the gradient of pressure and therefore the natural out flow of the BSS.

Aspiration flow control pumps allow a safer posterior peeling and a more complete peripheral shaving, explaining why the failure rate is lower. Phacoemulsification techniques have been mastered in order to improve extracapsular lens extraction. Flow control vitrectomy should be mastered as well for the efficiency and safety of vitrectomy.

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Email: ddd@club-internet.fr
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Didier Ducournau