The volume of gas required to ßush the vitreous cavity to achieve 97 % according to the axial length of the eye (Shunmugam et al. 2011).

Close the second sclerotomy. Keep some gas in a syringe (15 ml) to allow a top up of gas if some gas leaks during the disconnection of the infusion at the end of the operation.

Note: With small gauge surgery, remove both the superior trochars and check if they are sealed, then use a 28-gauge needle inserted into the pars plana to vent. This has the advantage that the superior sclerotomies can be checked for leaks whilst the air pump is still available before the exchange of gas. If you wait until after the exchange, there is only 15 ml of gas left in the syringe to sort out a leaking sclerotomy.

Note: Take care with the use of the three-way tap. Do not turn the tap so that the air and the gas syringe are in connection because air will enter the syringe and dilute your injection of gas.

Check the intraocular pressure with your Þnger tip (using the ÞngerÕs Pacinian corpuscles to assess the pressure!) aiming for 10 mmHg (your Þnger tip is a better pressure sensor in my view than pressing the eye with an instrument).

Always remove the infusion last. If the globe is soft, check for leaks from the sclerotomies, resuture if necessary. To elevate the IOP, add BSS to the anterior chamber via a paracentesis, or, if gas-Þlled, inject gas through the pars plana using a 30-gauge needle. Check the pressure again.

Full concentration ßuorescein dropped onto the conjunctiva will indicate a ßuid leak (the leaking ßuid dilutes the ßuorescein changing its colour from orange to green) and is especially useful when checking small gauge surgery wounds.

2.12Peroperative Complications

2.12.1 Iatrogenic Breaks

These must be identiÞed and treated to avoid postoperative retinal detachment. Apply retinopexy and gas tamponade. Overall, peroperative iatrogenic retinal breaks have been described in 10 % of vitrectomy patients (Carter et al. 1990), 5.5 % of patients operated upon for macular hole (Sjaarda et al. 1995), 20Ð33 % of those with diabetic tractional retinal detachment (Han et al. 1994) and 7.3 % of those with complex retinal detachment surgery (Afrashi et al. 2004). The complication is commoner in phakic patients and those without posterior vitreous detachment preoperatively (Dogramaci et al. 2012) and is a risk factor for postoperative retinal detachment in diabetic surgery (Gupta et al. 2012).

2.12.1.1 Causes

1.Bites of retina from the cutter produce moderate-sized round breaks. Care must be taken when removing the

Fig. 2.29 A postoperative detachment has been caused by an entry site break

vitreous in a bullous retinal detachment that the cutter does not bite mobile retina. Remove some SRF to reduce the height of the bulla, or splint the retina with some heavy liquid to reduce its mobility.

2. Tears from traction on the retina, for example, from membrane peel or posterior hyaloid membrane (PHM) peel in macular hole surgery. In epiretinal membrane peel, you can only pull on a membrane up to a force equal to the strength of the integrity of the retinal tissue, that is, the adhesion of the membrane retina must be less than the strength of the retina. Be careful if lattice degeneration is present not to pull the PHM through the lattice lesions as this will tear the retina.

3. Giant retinal tears from traction on the vitreous base. The vitreous base will not separate from the retina. Any force on the vitreous base, for example, from careless insertion of instruments, will take the retina with it causing a large retinal break.

4. Entry site breaks from vitreous incarceration into the sclerotomies. These may appear after the surgery as the vitreous is slowly drawn into the sclerotomy by postoperative Þbrosis, thereby producing traction on the retina and retinal tear formation. It is therefore important to remove as much vitreous as possible around sclerotomies and to excise incarcerated vitreous.

5. Scrapes on the retina from contact of instruments onto the retina. You must be aware of the spatial relationships of the inside of the sphere of the eye to avoid scraping the retina whilst moving instruments, for example, when performing peripheral panretinal photocoagulation. Moving peripherally in the eye requires a compensatory shortening of the length of the shaft of the instrument in the eye.