Fig. 2.27 View onto a fundus of an air-Þlled eye. The peripheral view is extended up to the ora serrata; the disadvantages are a lower resolution and the difÞculty to identify retinal breaks

Another indication for an air-Þlled eye is a better sealing of the sclerotomies. The air exerts pressure on the wedges of the tunnel sclerotomies and induces an improved closure of the sclerotomies.

A disadvantage of air and gases in general is the greater distortion of the optical image. One advantage is the wide-angle view up to the pars plana in an air-Þlled eye (Figs. 2.26 and 2.27).

Pits & Pearls No. 2

BIOM and air: When Þlling air into the vitreous cavity, the image is out of focus due to the different refractive index. If you move the BIOM lens up a little, the image becomes focussed again.

2.4.3Expanding Gases

SF6, C2F6, and C3F8 are expanding gases as dissolved nitrogen diffuses along the concentration gradient from the blood into the gas bubble and accumulates here. The postoperative extension may lead to strong increases in intraocular pressure when the gases are injected undiluted into the eye. To avoid this intraocular pressure rise, expanding gases are used in a concentration in which they do not expand.

Table 2.1 Properties of gases and liquids for a tamponade (Densiron 68¨ is heavier than Oxane Hd¨ (see density) but almost as viscous as 1,300 cSt silicone oil (see viscosity) and therefore almost as easy to remove)

The non-expanding concentration of SF6 is 20%, of C2F6 15%, and of C3F8 14% (see Table 2.1). Air does not expand. Patients with a gas-Þlled eye should not undergo anaesthesia with nitrous oxide, as it diffuses into gas-Þlled cavities and leads to an increase of volume. In addition, any air travel or trips to locations at greater heights (e.g., patients living in mountainous areas) are strictly prohibited. This should be part of any routine consent procedure before vitreoretinal surgery. We also advise on giving patients information leaßets with detailed instructions for themselves and referring physicians regarding these precautions.

SF6 (sulphur hexafluoride)

The commonly used concentration of sulphur hexaßuoride (SF6) is 20%. It tamponades the eye for approximately 4 weeks. Indication: macular holes, diabetic retinopathy, and retinal detachment surgery with superior breaks. SF6 is not suitable for inferior breaks unless a speciÞc posture can be maintained for prolonged periods of time (e.g., supine position or on one side opposite to the break).

C2F6 (perfluoroethane)

The usual concentration of C2F6 is 15%. It tamponades the eye for approximately 4Ð6 weeks. Indication: difÞcult detachments with multiple breaks, inferior tears, or PVR detachment.

C3F8 (perfluoropropane)

The usual concentration of C3F8 is 12Ð14%. It tamponades the eye for approximately 8 weeks. The indications are similar to C2F6.

Fig. 2.28 An expanding gas is injected through the IV line to the top right into the eye.

To the bottom right, a ßuid needle is held in a cannula to relieve intraocular pressure

Pits & Pearls No. 3

Injection of gas

1. Errors in preparing the correct concentration of the airÐgas mixture are potential recipes for disasters if different gases with varying concentrations are used regularly in one theatre. Concentration levels, which are too high, can lead to a massive rise in the intraocular pressure, whereas lower concentrations may result in a shorter tamponade than desired. In every theatre, a strict protocol for preparing the airÐgas mixture must be followed. We recommend that every surgeon supervises the preparation of the mixture and checks on the gas used.

2. Gases are in 100% concentration in gas containers. They must be diluted with air before injection into the eye. Example: 20% of SF6. 50 ml syringe: draw 10 ml 100% SF6 in the syringe and dilute to 50 ml with room air

3. If you intend to inject a gas into the eye, Þrst perform a ßuidÐair exchange. The gas-Þlled syringe is then connected to the three-way tap. The scrub nurse can inject the gas. At the same time you hold a ßuid needle behind the lens to release pressure so that the globe remains normotensive (Fig. 2.28). Always leave some 5Ð10cc in the syringe. This gives you some extra volume to inject should the globe be hypotensive after removing the trocars.

2.4.4Light Silicone Oils

Conventional silicone oil is lighter than water and ßoats in the vitreous and in the anterior chamber. Indications for silicone oil tamponade are retinal detachments with multiple (superior and inferior) breaks, a giant tear, advanced proliferative diabetic retinopathy, PVR detachment, and a macular hole (if a prone position is not possible).

support the inferior periphery. Indications are multiple inferior breaks, PVR detachment, retinal detachment with giant tear, and a traumatic detachment.

Since Oxane Hd¨ and Densiron 68¨ consist partially of PFCL, they should not come in contact with pure PFCL for longer periods of time. However, a short contact (e.g., during direct PFCL heavy silicone oil exchange) is possible. Oxane Hd¨ should be removed after 2 months and Densiron 68¨ after about 3Ð4 months as their tendency to emulsify is comparable to 1,300 cSt conventional silicone oil. The features of these tamponades are summarized in Table 2.1.

Important: There is no 100% tamponade, neither for gases nor for oils. This is because any tamponade will form the smallest possible surface, thereby forming a