9.2.4Surgery

Additional Surgical Steps

Peel posterior hyaloid membrane off retina (in grade 2 and 3 holes).

Stain the internal limiting membrane (ILM) with brilliant blue.

Remove ILM. Insert air.

Insert long-acting gas.

Table 9.1 Difficulty rating of PPV for macular hole

9.2.4.1 Introduction

In macular hole surgery, vitrectomy is performed (Kelly and Wendel 1991). A gas bubble is inserted to tamponade the hole. During the first week, the patient may have the inconvenience of positioning their face towards the ground, allowing the bubble to float against the hole. Many other manoeuvres have been added to this procedure to try to maximise the chances of hole closure, such as dissection of the internal limiting membrane from the retina or application of autologous platelets to the hole (platelets obtained from the patient’s blood by spinning, separation and alliquoting). Successful closure of the hole arrests progression to a stage 4 hole and frequently reduces the distorting effects of the hole and improves vision.

9.2.4.2 Surgery

Once the core vitrectomy has been performed, detach the posterior hyaloid from the retina in all macular holes except grade 4.

9.2.4.3 Peeling the Posterior Hyaloid Membrane

Detect preoperatively whether the posterior hyaloid has detached or not. This will save time and anxiety during the operation. Remove as much vitreous as possible over the optic disc. If there is too much cortical vitreous overlying the hyaloid membrane, the vitreous will engage in the port and shred without pulling up the hyaloid. The membrane needs to be engaged to start the detachment process. Use the vitrectomy cutter on aspiration, place the tip near the optic disc so that it is almost touching the disc and aspirate on 150–300 mmHg

vacuum. Allow a moment for the hyaloid to engage and then move the cutter 1 mm tangentially over the optic nerve rim taking care not to touch the nerve or retina. Then, move the cutter tip towards the centre of the eye. Keep trying different parts of the optic nerve head until suddenly a ring indicating the juncture of the attached and detached hyaloid is seen circumferential to the disc margin. Observe the ring, and again aspirate over the nerve; this time, pull further into the centre of the eye; see the ring increase in size as the detachment spreads to the equator of the globe. Early in this process, create a hole in the elevated posterior hyaloid membrane to allow vitreous cavity fluid to enter between the PHM and the retinal surface. This breaks the ‘vacuum’ between the PHM and the retina and aids elevation of the rest of the PHM to the periphery.

Note: Make a hole in the centre of the posterior hyaloid to allow fluid to enter between the PHM and the retina.

It should now be possible to see the posterior hyaloid floating in the vitreous cavity. Continue the detachment process by aspirating the hyaloid into the four quadrants of the eye. If this is not working or the instruments are getting close to the lens, use the cutter to remove the central membrane, place the cutter through the hole and aspirate the posterior aspect of the hyaloid in each quadrant and lift the membrane towards the periphery. Stop before the insertion of the vitreous base because the vitreous will not detach any further, forcing it anteriorly will cause retinal tearing. Similarly, do not pull through abnormal vitreoretinal attachments such as lattice degeneration because traction on these will cause retinal tears. Instead, trim the vitreous around these adhesions. Once the posterior hyaloid has been detached, remove the vitreous and hyaloid. It is especially important to search for breaks by internal search after surgical PVD. The tears are often easy to find because they are of moderate size with often a ragged appearance and may bleed.

In stage 4 holes, the posterior hyaloid will present a distinct peripheral edge; if you do not detect such an edge, then the hyaloid is probably not detached and posterior suction should be tried.

Note: Occasionally, the PHM is very difficult to elevate off the disc (usually in conditions other than macular hole). In this case, stain the vitreous with membrane blue to help its visualisation; trim it down so that there is minimal cortical gel. Repeat the aspiration with the cutter; increase the vacuum to 300 or 500 mmHg. Rarely, you may need to grasp the vitreous with forceps; however, it is possible to damage the retina by touching it with the instrument or by pressure from the instrument tip transmitted to the retina through the residual cortical gel. It is, however, not acceptable to leave the PHM on the retina as later separation will occur with the risk of retinal tear formation and RRD; therefore, every effort must be made to achieve vitreous separation.

Fig. 9.42 When starting the posterior hyaloid peel, go to the edge of the optic disc, try to engage the posterior hyaloid and then elevate away from the disc. Arrows shows movement of instrument

Fig. 9.43 Peel a posterior vitreous detachment in the centre of the eye going towards the back of the lens (a and b, black arrows indicate direction of force). Once the core of the vitreous has been removed, the infusion fluid has access to behind the posterior hyaloid membrane (c). By making a hole in the posterior hyaloid membrane, the fluid can pass through (dashed arrow). This will aid dissection of the posterior hyaloid membrane by the infusion fluid. Once the PVD is more established, an instrument such as a cutter can be inserted through the hole and the membrane elevated along an axis tangentially to the retina, in each quadrant (d). Commencing the PVD peel is safe. Commencing the posterior vitreous hyaloid is performed at the optic disc. Pull perpendicularly away from the disc to commence the peel. A ring of attachment is seen around the disc. This will expand as the hyaloid detaches, and this should be watched more to confirm elevation of the membrane

Surgical Pearl of Wisdom

For safely inducing a PVD in macular hole surgery When inducing a PVD during macular hole surgery,

start with the bottle raised 30 cm above normal and 300 mmHG suction; engage the hyaloid nasal to the disc, but watch the operculum over the hole; this is almost always present, and when this starts to lift, you know you are in business. Then, only pull until the retinal wave is just outside the arcades and proceed with the vitrectomy at 150–200 mmHG suction with the bottle at normal height. The vitreous will gently hydrodissect away from the retina without any further pulling, thereby avoiding/minimising iatrogenic breaks.

D. Alistair H. Laidlaw, St Thomas’ Hospital, London,

UK

Fig. 9.44 The edge of the posterior hyaloid (arrow) peeling off the retina can be observed during PVD induction and is a good guide to the extent of PVD produced

Fig. 9.47 Do not pull the membrane as shown by the (blue arrows) as this will cause traction on the opposite retina (red arrows), and if there are any, retinal adhesions may increase the chance of retinal tear formation. Similarly, when the PVD peel is just started, do not pull tangentially across the retina as this runs the risk of producing forces at the vitreous base which could tear

Fig. 9.48 When commencing the ILM peel, incise as shown to minimise damage the nerve fibres in the nerve fibre layer

Fig. 9.49 To start the ILM peel, perform a slight incision of the ILM temporal to the fovea (a and b). In this area, you are less likely to slice nerve fibres and cause small paracentral scotoma. Alternatively, use a diamond-dusted brush to start the ILM peel. Once the ILM is lifted, remove it further in the fashion of the capsulorhexis going around the fovea in a circular fashion (c and d). To maintain an intact ILM during peeling, first, pull perpendicularly to the edge of attachment of the ILM to the retina, and, second, readjust the forceps every so often so that you are grasping the membrane close to the edge of attachment. Angled forceps allow you to see the point at which to grasp the ILM. Be careful that you intermittently check the position of the heel of the forceps to avoid damaging retina with this whilst you are distracted by the ILM peel

Fig. 9.51 When peeling the ILM, pull in a perpendicular motion to the edge of the torn ILM; this encourages the ILM to tear around the hole in a circumferential way as the top graphic shows. Do not pull the edge over the hole or the ILM will tear towards the hole as shown in the bottom graphic reducing the quantity of ILM that you will remove and requiring a regrip of the ILM at another site

Fig. 9.50 When starting an ILM peel, you can use the flat edge of the MVR blade to scrape the surface; because the ILM is relatively stiff, this will induce a small hole to appear providing an edge to allowing forceps to grasp the ILM. The ILM is so close to the underlying nerve fibres that trying to insert a blade under the ILM to start lifting is very difficult and should be avoided

Fig. 9.52 Aspirate on the disc to engage the PHM. Watch the PHM peel from the retina. When applying any dyes to the macula, apply the dye away from the fovea in the first instance to avoid damage to the retinal pigment epithelium and to avoid insertion of the dye underneath the retina. Using a contact lens provides high magnification and enhanced depth perception to incise the ILM. Peel the ILM, search the peripheral retina and fill with gas (see Figs. 9.53–9.58)