5.2.1 PFO Indications and Complications

To minimize complications from using PFO, it is advised that during vitrectomy, the following instruments also be used:

• Valved cannulas, to decrease the turbulence of the BSS infusion fluid into the eye and minimize the formation of small or peripheral bubbles (“fish eggs”) that can migrate subretinally through a retinal break
• Wide angle or panoramic viewing to be able to visualize the peripheral edge of the PFCL bubble as it nears retinal breaks, as well as to have excellent visualization during fluid-air exchange
• A dual bore cannula for injection of PFO.[5] The PFO exits from the side of the tip of the cannula. In small gauge vitrectomy, this instrument has several venting sideports along the shaft to reduce the intraocular pressure during injection (Figure 5.2.1)

• High pressure tubing allows for an assistant to hold the syringe and control the injection speed while the surgeon manipulates the cannula. This allows for greater control of the large syringe. The VFC cannula on a low injection pressure can also be used to control PFO injection with the foot pedal

• PFO should be injected when the retina is mobile, and preferably when the retinal breaks are seen. In cases of a “closed or narrow funnel” configuration in PVR, a viscoelastic (e.g. Healon®) would be a better tool to open up the retinal folds for posterior epiretinal membrane peeling. Once the posterior preretinal membranes are removed and the retina is mobile, PFO can be used to flatten the retina
• Be sure a posterior vitreous detachment has been confirmed before injecting PFO as the bubble may trap the hyaloid if not previously elevated
• When injecting PFO, the injection should be slow, maintaining the tip of the injection needle within the PFO bubble so it grows as one large bubble. The optic disc should be observed and if the central retinal artery closes or pulsates, the rate of injection should be slowed. Watch the retina flatten. It is not necessary to fill the vitreous with one injection – inject to a comfortable level, and then add PFO as necessary during the operation (Figure 5.2)

• When inserting or withdrawing the injection cannula, keep the tip away from retinal breaks to minimize the chance that some drops of PFO could leak and pass subretinally through retinal breaks. Consider injection through a trocar where the canula does not need to traverse a large retinal break if possible. Always maintain a degree of negative pressure on the syringe while traversing retina prior to the reaching the injection site as without negative pressure, PFO often leaks out of the canula. When performing fluid-air exchange also always keep a slight negative pressure on the extrusion canula at all times when entering and exiting the eye to prevent unintentional PFO leakage
• When injecting, make sure to roll / “squeegee” the fluid out by rocking and injecting the PFO first on the area where there is less subretinal fluid
• In addition to avoiding a posterior retinotomy, the PFO flattens the posterior retina and reduces mobility of the retina so that vitreous traction can be thoroughly removed from the flap of retinal tears and the peripheral vitreous can be shaved down. It thus aids in vitrectomy in sticky hyaloids where the retina also happens to be highly mobile
• As the PFO level rises be aware that mechanical manipulation of the globe (e.g. scleral depression) may cause PFO bubbles to form at the peripheral surface. Reduce the infusion pressure if bubbles frequently form
• Make sure to remove all traction over retinal breaks before lifting PFO over the break as a break with unrelieved traction will act as a sink for subretinal PFO

As PFO fills the eye:

• Residual preretinal membranes can be visualized and peeled under PFO
• Shave peripheral vitreous down to reduce the potential for anterior PVR (Figure 5.2.3)

• Examine the retinal periphery for any retinal breaks, or signs of residual traction that requires a relaxing retinotomy or membrane peeling. If the PFO is unable to flatten the retina in an area, this suggests some residual traction exists. In these cases, PFO often adopts an ovoid rather than a spherical configuration
• If a small peripheral break cannot be located, PFO can displace the subretinal fluid through the break and reveal it (“Schlieren phenomenon”). Diluted trypan blue can also be injected subretinally using a 41-gauge cannula and when PFO flattens the retina, the blue fluid exits through the retinal break
• In eyes with retinal incarceration following open globe injury, shave vitreous completely at the incarcerated site
• If all traction on the retina has been released, PFO can be added above the level of any retinal breaks. This facilitates laser of the breaks (especially retinotomies) since visualization is better (Figure 5.2.4)

• Laser under PFO where possible to treat the retinal breaks and the laser burns will make the retinal breaks more visible during fluid-gas exchange. Additional laser photocoagulation is often necessary under air (when the view will widen) to treat the most anterior aspects of the break