2.4 Gases and Liquids

¥Proliferative diabetic retinopathy: air, 20% SF6, or light silicone oil

¥Primary retinal detachment: very often: 20% SF6, sometimes: 15% C2F6

¥Redetachment: 15% C2F6, 14% C3F8, light silicone oil, and heavy silicone oils

Air/gas tamponades are absorbed over several days to weeks. The gases differ in the duration of tamponade: Air 1Ð3 days, SF6 tamponades approximately for 3Ð4 weeks, and C2F6 and C3F8 tamponades about 1 and 2 months. Silicone oil tamponades are permanent tamponades and are usually removed between 4 weeks and 6 months after the initial surgery. Silicone oils with a lower viscosity (1,000 cSt conventional oil or heavy oils, which are a mixture of 1,400 cSt conventional oil and a heavy liquid) tend to emulsify earlier and are usually removed within 3 months. An advantage of these lower viscosity silicone oils is that they can easily be injected and removed with 25and 23-gauge ports. Higher viscosity 5,000 cSt silicone oils tend to emulsify later and can usually be left in within the vitreous cavity for longer periods of time. This usually requires at least one 20-gauge port for injection or removal. Very occasionally, 5,000 cSt silicone oil has to be left intraocularly as a permanent tamponade in cases with multiple redetachments after previously attempted oil removal or severe hypotony.

Gases and conventional silicone oil tamponade breaks in the superior periphery from 8 oÕclock over 12Ð4 oÕclock. Oxane Hd¨ and Densiron 68¨ are suitable for support of the inferior periphery from 4 over 6Ð8 oÕclock.

Caution: Inject gases or liquids slowly into the eye (and never on the macula), as the injection pressure can cause retinal necrosis.

2.4.1Perfluorocarbon

Perßuorocarbon (PFCL, heavy liquid) is heavier than water; the eye is Þlled up from the posterior pole to the ora serrata. In the supine position, PFCL exerts the most pressure on the posterior pole and less pressure anteriorly (Fig. 2.23); it ßattens the retina from the posterior pole to the ora serrata (Fig. 2.23). A big advantage is the good visibility under PFCL. One disadvantage is that it always needs to be completely removed, as it is retinotoxic if left within the eye for weeks to months, especially if it is dislocated into the subretinal space. PFCL is now an essential tool in retinal detachment surgery. It is used to ßatten the detached retina and push subretinal ßuid through the breaks into the vitreous. Additional advantages are an instant apposition of photoreceptors and retinal pigment epithelial cells in order to promote reattachment and facilitate laser treatment around the breaks. It also stabilizes the detached retina, thereby facilitating trimming of the vitreous base and decreasing the risk of iatrogenic breaks during surgery. Because it does not mix with vitreous, it clearly delineates vitreous remnants in the anterior periphery. One can Þll PFCL over the break without any problem; it will not spill through the break in the subretinal space due to its high surface tension. Finally, it can be used as a protectant of the posterior pole in cases of dislocated IOL or lens matter. Inject a small bubble of PFCL on the posterior pole in order to perform any necessary manipulations in these cases in some distance from the macula.

Fig. 2.23 Opposite effects of air and PFCL in the vitreous cavity. Air exerts pressure onto the retina from anterior to posterior, whereas PFCL exerts pressure from posterior to anterior

air

water

PFCL

Dislocation of PFCL into the subretinal space can occur in two situations: If there is a large retinal break with signiÞcant residual traction on the retina or if one injects PFCL too briskly, thus splitting the PFCL stream into multiple small bubbles that can then be ÒblownÓ through the break into the subretinal space.

Pits & Pearls No. 1

Injection of PFCL: There are two methods. (1) Bimanually: Using a backßush instrument cannula (Fig. 2.24) and a 5cc syringe. During injection, release pressure from the second trocar with a ßuid needle. Otherwise, you create a dangerous excess pressure in the eye. (2) Monomanually: Injection with a double-barreled cannula (Fig. 2.25). A double-barreled cannula enables injection of ßuid whilst maintaining the intraocular pressure. When ßuid is injected, the intraocular pressure rises; this pushes ßuid out of the eye through the second opening within the cannula. An intraocular hypertension is NOT possible. Therefore, only one hand is needed for injection with a double-barreled cannula (DORC. EFTIAR, dual bore cannula, 23 gauge/0.6 mm).

2.4.2Air

In the supine position, air exerts the most pressure on the anterior retina (ora serrata) and less on the posterior retina (Fig. 2.23). Because air is lighter than water or PFCL, the eye will be Þlled with air from the ora serrata and then down to the optic disc. To Þll the eye completely with air, the surgeon must aspirate the liquid behind the