which case the completion of the drainage is lengthier and technically more complex (see below, Sect. 35.5).

•When injecting into an eye that has a foreign object18 in the vitreous cavity, avoid pouring the PFCL on top of, rather than around and underneath, the object.

35.3.2.2 Removal19

The PFCL bubble has very low resistance to flow and readily escapes the eye,20 regardless of what replaces it. PFCL is also easy to discern, irrespective of what it is interfacing with. It is used almost exclusively as an intraoperative tool, although occasionally left behind21 for a few weeks.

•The larger the bubble, the flatter its anterior contour; a smaller bubble will form a sphere.

–During the initial phase of the removal the apparent spread (horizontal dimension) of the bubble is unchanged, only its height22 seems to decrease.

•Obviously, the deepest point of the eye is where the bubble will be easiest to collect. However, the eye is often rotated during removal and the single large PFCL bubble may break up into smaller ones, which lose connection with each other; these must then be aspirated separately.

•Residual PFCL bubble in the vitreous cavity: not a per se indication for removal.

•Residual PFCL bubble subretinally: not a per se indication for removal.

–If it is subfoveal, though, it should be removed as it may be toxic. A small retinotomy is sufficient, and the bubble will readily escape.

•Residual PFCL bubble in the AC: easy to recognize since in a patient sitting at the slit lamp the bubble will be inferior. A small inferotemporal paracentesis will result in spontaneous drainage (see below, Sect. 35.6).

35.4Silicone Oil

Silicone oil is used as a temporary or permanent substitute. Its major drawback is that in the former case the patient must undergo a second operation to remove the oil. “Oil changes” are also needed if the longevity of the oil23 is shorter than its required duration. The choice between silicone oil and gas tamponade in RD surgery is discussed under Sect. 54.5.2.5.

18Which needs to be levitated; see above.

19See below for additional details about exchanges.

20This includes PFCL that is under the retina (see below, Sect. 35.3.1.2).

21“Double fill,” with 1,000 cst silicone oil as the counterpart. The potential problem with such a mixture is that the two materials will not completely fill the vitreous cavity, leaving space between them and thus allowing the proliferation to develop in-between – i.e., centrally.

22The bubble height is indicated by the interface seen on the shaft of the flute needle.

23Emulsification, see below.

35.4.1 Selecting the Type of Silicone Oil to Implant

Silicone oil is available in “normal” viscosity (1,000–1,300 cst) and high viscosity (5,000 cst; see Sect. 14.3.1). The more viscous the oil, the less likely it is assumed to emulsify.24 The normal oil provides better tamponade superiorly, the heavier- than-water version inferiorly.

•I use almost exclusively normal oil (lighter than water and low viscosity).

–The only exception is eyes that require a permanent fill (see below), in which case I use 5,000 cst oil.

•I do not use heavy oil.

–While heavy silicone oils can indeed prevent inferior proliferations, they increase the risk superiorly, where they are technically more difficult to access and deal with.

Q&A

Q Long-acting gas or silicone oil?

AFor me this is a rather easy question to answer. If an eye requires longterm (months) tamponade, I prefer oil (see Table 35.1).

35.4.2 General Considerations

•A silicone oil fill is supposed to 100% (see below and Sect. 14.3.2).

–A less-than-complete fill increases the risk of emulsification and the likelihood that the cells responsible for proliferation will aggregate inferiorly (hence the rationale to use heavy oil).

•Unless the oil is to be kept permanently (see below), the patient must understand that oil implantation involves at least one additional operation.

•The patient has to accept that the eye’s refraction will be significantly changed by the oil’s presence.

•If there is a risk of oil prolapse into the AC, the patient may have to position (facedown) in the first few days.25

•Decide, preferably in advance, the fate of the lens (see Sect. 4.5). Ideally, measure the axial length prior to surgery, when there is no silicone oil in the eye.26

24Emulsification is also dependent on other factors such as silicone oil purity, the completeness of the fill (100% fill representing the smallest possible risk), the patient’s lifestyle etc.

25If the eye is aphakic and silicone oil prolapsed into the AC intraoperatively, the pupil must not be constricted as long as there is oil in front of it.

26Unless there is significant cataract, the axial length can be measured under oil with the LenStar (Haag-Streit AG, Koeniz, Switzerland).