•Visco: whether being left over from cataract surgery or used to keep silicone oil from prolapsing into the AC (see Fig. 14.5), it can interfere with visualization if it is uneven or contains air bubbles.

25.2.2 Pupil

The BIOM represents a huge advantage over the contact lens by allowing adequate visualization of the retina even if the pupil is small. Still, a wide pupil has tangible benefits for the surgeon. There are several methods to achieve pupil dilation on the operating table if the preoperative medication has been ineffective or the drugs used during general anesthesia caused secondary miosis.

25.2.2.1 Mechanical Forces Preventing Pupil Dilation

•A fine retropupillary membrane or fibrin may be the culprit. In such cases, gentle pulling on the iris margin with forceps (see Fig. 48.1c, d) or blunt dissection with a spatula may help. The surgeon must carefully observe how the tissues behave to avoid tearing the iris or rupturing the anterior lens capsule if posterior synechia is present, and switch to a sharp instrument if there is a risk.

–A retroiridal fibrinous membrane is dangerous to forcefully pull on since the surgeon has no visual feedback about the consequences of his action until it may be too late.

•If fresh posterior synechia are present (see Sect. 39.4), usually a blunt spatula is utilized to break it. However, especially after trauma, it may be preferable to use scissors and cut the tissue responsible, sometimes preceded by endodiathermy12 to prevent bleeding.13 Limited amounts of visco can be injected to create space for the scissors between the iris and the capsule or control the bleeding.

Pearl

Never inject visco under the iris in order to try to break posterior synechia or separate a fibrinous membrane from the iris back surface: by doing so, you simply give up control over events (see Sect. 3.2). The visco will go wherever the resistance to its flow is the weakest, tearing some tissue (where it wants to, not where you would prefer it to) or disappear posteriorly.

25.2.2.2 Intracameral Adrenalin or Visco

If it is not synechia or a membrane (see above) that prevents iris dilation, intracameral adrenalin14 usually works. Repeated injections of the drug, however, do not

12The blood vessels may be present on either surface of the scar or inside it, hidden from view.

13As a general rule, the more chronic (old) the synechia, the greater the need to use sharp, rather than blunt instruments.

14In a concentration of 0.01%.

help: the effect is typically one time. In older patients adrenalin occasionally constricts, rather than dilates, the pupil.

Visco may dilate the pupil and keep it so, but may also interfere with visualization (see above, Sect. 25.2.1).

25.2.2.3 Iris Retractors15

These are very potent weapons to widen the pupil and keep it wide throughout the case, and they can be used even in the phakic eye. A few caveats are worth mentioning.

•The angle at which you created the paracentesis with the needle16 is crucially important. The retractor is too delicate to allow substantial modification to its trajectory once you pushed it past the intracorneal channel you just prepared.

–When you create the channel, keep in mind the parallaxis phenomenon. Viewing from above, the instrument inside the AC gives the false impression that the tool is at a shallower angle (closer to the cornea) that it really is. Compensate for this when deciding the angle of penetration.

•Do not use toothed forceps to grab the retractors.

•Upon insertion, hold the retractor close to its hook (the working end) to avoid bending it. Never grab the hook itself.

•Keep the disc on the retractor close to the proximal (nonworking) tip of the retractor, never at the distal end: not all retractor types allow reinsertion of the shaft into the disc if it has been accidentally pulled off.

•Save time by creating all17 paracenteses first, then place all retractors on the conjunctiva, and finally insert them.18

•Once the retractor is at the iris margin, you can slide the little hook laterally in either direction, with the paracentesis as the fulcrum point, before actually pulling the iris with the hook.19

–If it is difficult to catch the iris margin, use the neighboring paracentesis channel and insert a second retractor, lift the iris, hook the iris there with the first retractor, and then slide it to place. Otherwise do not lift the iris until all (4) retractors are in place.

–Weak posterior synechiae can be broken by the retractor, but a strong one or a retroiridal fibrinous membrane may prove too strong for the hook (see above), which straightens rather than lifts the iris margin.

15See Sect. 39.1 about the rules of paracentesis.

16If for retractor use, I prefer making the paracentesis with a 25 or 27 g needle instead of a blade.

17It is not always necessary to insert all 4 (or 5, since certain manufacturers supply 5 in the box) retractors. Plan the number and location in advance and use the fewest possible.

18Collect them in the same way upon removal; then hand back all of them together to the nurse, rather than doing it one by one.

19In other words, it is not necessary to hook the iris at the exact location where the retractor first caught it.