Fig. 14.1 Pneumovitrectomy for the “vitreous skirt” in the periphery. The image is slightly different in the air-filled eye if vitreous is still present. On the left side, pneumovitrectomy has already been done and the remaining vitreous skirt is greatly trimmed; to the right, where the probe is held, the skirt is still rather thick. All this is readily visible under air; if BSS is used, the remaining vitreous is largely unnoticeable

Complications9: High IOP (see above) and cataract; the latter (“gas cataract”) may be temporary (see Fig. 14.2). Rarely, a visual field defect develops.10 Gases may also enter the subretinal space, but this is less common than with air, due to the high surface tension of the gas.

Fig. 14.2 Gas cataract. Typical image of the lens feathering due to long vitrectomy or gas implantation. With very rare exceptions, the condition resolves spontaneously with time

14.3Silicone Oil

Providing long-term11 tamponade, the oil can be both a prophylactic and a therapeutic tool.

9Employing gas of erroneous concentration (see Chap. 6) is a complication due not to the gas but to the nurse (just remember, it is still the surgeon who is ultimately held responsible for it).

10Probably due to the drying of the retinal surface.

11Weeks, months, or permanent, depending on the indication and the eye’s condition, see Table 14.1.

aOnly a selected few examples are included here.

bThere is no need for positioning as long as the fill is 100%.

cIt is rather common that, due to the recurrence of the condition, “oil exchange” is necessary, extending or multiplying the periods with silicone oil fill.

dOn a personal note: This is my only indication to use 5,000 cst oil. eSee Sect. 13.3.1 for more details.

14.3.1 Types of Silicone Oil

•Viscosity: The two typical options are 1,000/1,300 cst and ≥5,000 cst.

–Higher viscosity is assumed to delay the time to emulsification.12

–The higher the viscosity, the more difficult to inject, and especially extract, the oil.

•Molecular weight: Standard vs “heavy” silicone oil.

–The standard oil13 has a specific gravity of 0.97: it floats on water (BSS, aqueous).

–The “heavy” oil has a specific gravity of 1.02–1.06: it sinks in water (BSS, aqueous).

14.3.2 Achieving a 100% Fill14

The oil is supposed to be in contact with the retina,15 ciliary body, zonules, and the posterior capsule (iris in the aphakic eye) over their entire surface. To achieve this, the surgeon needs to do the following.

•A meticulous exchange between the current intravitreal content (typically air) to silicone oil.

–In fact, the goal is a slight overfill, as measured by the IOP,16 to compensate for the postoperative increase in the volume of the vitreous cavity.17

Q&A

Q What is the true benefit of a 100% silicone oil fill?

AIn principle, cells cannot accumulate and proliferative membranes cannot form: the risk of PVR development is reduced.

•Prevention of silicone oil loss at the time of cannula removal (see Fig. 14.3).

– A second reason for this is to prevent oil accumulation under the conjunctiva.18

12The key word here is “assumed.” Emulsification depends on many other factors as well, and it is not uncommon to see early emulsification even with higher viscosity oils.

1337 kDa molecular weight as opposed to the 74 kDa molecular weight of a heavy oil.

14The technical details are provided in Sect. 35.4.

15A scleral buckle represents too great a change in the curvature of the eyewall for the silicone oil to follow; in an oil-filled eye there is always a small ring of aqueous at the bottom of the central slope of the indentation.

16I typically aim for 30 mmHg.

17The temporary, intraoperative “loss” of the volume of the vitreous cavity is caused by increased choroidal thickness due to increased blood flow. Additional factors may include epiretinal blood, posterior dislocation of the iris/lens diaphragm (e.g., due to air or viscoelastics in the AC) etc.

18Which can give foreign-body sensation to the patient; young women also often complain about the eye “looking ugly” (see Sect. 35.4.4).

b

If the fill is incomplete, a crescent of aqueous is found, in the erect patient, at the bottom of the eye.19 Inflammatory debris collects in this pool of fluid, increasing the risk of PVR.

Pearl

The use of heavy silicone oil shifts the pool of fluid superiorly. With the use of standard oil, the PVR starts inferiorly; it is shifted superiorly with heavy oil (see Table 14.2).

With silicone oil use, there are important questions related to the lens20 (see

Table 14.3).

19Depending on the degree of the underfill and the size of the pupil, the oil meniscus can actually be visible at the slit lamp.

20The surgeon must keep in mind that an unexpected complication can always force him to implant silicone oil, even if this was never in the original plan.

aSee Sect. 4.5.

bEmmetropic eye and a patient over 45–50 years of age; different answers apply in cases of hyperopia or low myopia, and younger age; the patient should decide.

cNot needing refractive correction. This may be controversial suggestion, but I fail to see the benefit of implanting a 0 D IOL (see Sect. 42.1).