Pits & Pearls No. 10

Blood in the anterior chamber: If you experience a bleeding during the PPV into the anterior chamber, you can either aspirate the blood with irrigation or aspiration instruments or inject a viscoelastic gel into the anterior chamber to push the blood to the edge of the anterior chamber and tamponade the bleeding. Ask the scrub nurse to remind you to remove the viscoelastic at the end of the vitrectomy. It is important to do this before you instal the tamponade, as the removed viscoelastic has to be replaced by fluid, which again will enter the posterior chamber and displace the tamponade.

Pits & Pearls No. 11

DVD

Video 3 Special techniques for the anterior chamber

Blood clots in the anterior chamber: If the bleeding has stopped, extract fibrous strands of blood with an Eckardt forceps through a paracentesis.

3. Focussing

The surgeon or the scrub nurse flicks in the BIOM. Next, the light pipe is introduced in the temporal trocar towards the macula, until the pupil is bright. Then, the inverter is activated, the microscope light turned off and the image is focussed.

For beginners, it may be frustrating to adjust the focus at the beginning of vitrectomy. However, if you keep a few rules in mind, you will find focussing easy. There are three adjustable parameters: (1) Focus wheel at the BIOM, (2) focus on foot pedal of the microscope, and (3) zoom on foot pedal of the microscope (Fig. 4.7). When focussing the image, you should only change the two parameters, focus wheel BIOM and focus foot pedal, and NOT the zoom. You should only change the zoom when you have a sharp image.

Remember following steps

1. Minimal zoom.

2. Turn the BIOM-adjustment body with the focus wheel to the top position.

3. Move the microscope with the focus foot pedal so far down towards the cornea until you get a fairly big image (red pupil).

4. Turn the focus wheel (BIOM) until you get a sharp retinal image.

If the image is sharp, move the microscope further down towards the cornea with the focus of the foot pedal (Cave: corneal touch!). Lastly, you can increase the zoom with the zoom pedal, but be aware that the resolution decreases the more zoom you have.

If the image is totally blurred and you eventually cannot continue, or you changed the front lens, always return to the initial parameters (lowest zoom, BIOM adjustment body to the top).

Fig. 4.7 A surgical microscope with attached BIOM. Integrated is an inverter, which may be operated manually or by foot pedal. At the front of the BIOM, the interchangeable front lenses are attached. The adjustment body can be adjusted with the focus wheel

Inverter

Adjustment body

Focussing wheel

Front lens

If you are using the EIBOS system, try to reach the manual focus with your right index or middle finger. Once you have mastered this, it makes focussing a lot easier than advising the scrub nurse in focussing up or down.

Pits & Pearls No. 12

Corneal lubrication: A major problem during vitrectomy, especially in combined surgeries with a duration of over 1 h, is corneal epithelial oedema. With the application of methylcellulose (Celoftal, Alcon) on the cornea, the cornea can remain clear for many hours. A debridement of the epithelium is rarely necessary, but if needed, use a broad blade (crescent knife).

Pits & Pearls No. 13

Small pupil: If the pupil contracts during surgery, inject 0.01% Adrenalin into the anterior chamber. The pupil should enlarge within seconds. If the small pupil is caused by posterior synechiae, use stretching instruments such as a push-pull or insert iris hooks to enlarge the pupil.

Pits & Pearls No. 14

BIOM and air: If you perform a water against air exchange, the image will become blurred. You can focus the image by turning the focus wheel of the BIOM so that the front lens moves up. The image will become focussed again.

4. Core vitrectomy

DVD

Video 4 Difficult PVD

Here, we start at with the core vitrectomy. In contrast to cataract surgery, you will be surprised by how much space you have in the vitreous cavity. In contrast to phacoemulsification where you hold the instruments almost horizontal, you hold the instruments during vitrectomy almost perpendicular (towards the optic nerve). The settings can be adjusted according to the individual preferences and the vitrectomy machine. For details, see Table 4.2.

We usually start with the removal of the central vitreous (‘core vitrectomy’) in order to have enough vitreous body for the subsequent posterior vitreous detachment. It is also important to clear the vitreous immediately in front of your ports. Otherwise, there is the danger of pushing the vitreous base forward when introducing your instruments, thereby causing retinal breaks in the vitreous base. This is of particular importance when introducing blunt instruments, for example, a fluid needle or injection needle.

Table 4.2 Approximate settings for 23-gauge with different vitrectomy machines

Pits & Pearls No. 15

Subepithelial location of infusion cannula: Even an initially correctly placed trocar cannula may move subepithelially during a later stage of the operation. If you experience a retinal or choroidal detachment, stop the infusion, remove the infusion line, and insert it in a safe trocar cannula. Re-open the infusion and the retina or choroid will reattach. Now check the location of the infusion cannula. Is it 3.5 mm posterior to the limbus? If not, replace the trocar cannula correctly. Is the trocar located subepithelially? If so, then free the trocar from the tissue with a membrane pic inserted in the opposite cannula.

5. Induction of posterior vitreous detachment

For this step, we routinely use a 90D front lens. To induce a posterior vitreous detachment is a difficult procedure in the learning phase. We therefore recommend staining vitreous first with triamcinolone or trypan blue. The vitreous body is then much easier to identify and the induction of posterior vitreous detachment significantly easier.

For induction of PVD, position the vitreous cutter just in front of the optic disc, then increase suction (foot pedal to bottom position) to a maximum. In the suction phase, the cortex and especially the posterior hyaloid will be engaged in the aspiration port. Then draw the vitreous cutter slowly with maximal suction towards the lens. If the manoeuvre is successful, you will see a kind of fine silk screen that moves forward together with the vitreous cutter. Sometimes, this whole manoeuvre must be repeated several times until it succeeds. Before you repeat the manoeuvre, cut the aspirated vitreous in the vitreous cutter to prevent traction and tractional tears and then place the vitreous cutter in front of the optic disc again.

Pits & Pearls No. 16

PVD

1. The correct assessment of the relationship between the posterior vitreous face and the retina/optic disc is one of the key steps to master pars plana vitrectomy. Always check if a PVD is present or not. Even in cases when you expect a PVD to be present (for example, retinal detachments), you will sometimes be surprised by an attached vitreous face.

2. The freshly detached posterior vitreous face has a ‘beaten metal’ appearance. You know that you have induced a PVD if you see this appear on the posterior surface of the vitreous. When a PVD is induced, suddenly, a lot more vitreous, which must be removed, will appear in the vitreous cavity.