Fig. 12.18 Traction on the retina can create a retinal break as in this patient who has an avulsed blood vessel and an operculum on the nasal side of the disc overlying a retinal hole. Often as in this eye, progression to RRD does not occur; this may be due to the stiff, immobile vitreous in diabetes. The immobility of the vitreous prevents the creation of ßuid currents thought to be necessary for SRF to accumulate

Fig. 12.19 Unfortunately, despite the advantages in screening and in treatment by panretinal photocoagulation, patients still attend with very severe tractional retinal detachments as seen in this picture. The appearance can be deceptive with dissections easier than at Þrst apparent. As with all diabetic tractional retinal detachments, the key is determining the right layer and getting behind the posterior hyaloid, membrane and cortex. Elevation of cortex remnants in a vitreoschisis aids removal of the vitreous gel and reattachment of the retina

12.2.4 Diabetic Retinal Detachment

12.2.4.1 Clinical Features

As in other epiretinal membranes, Þbroblasts within the vascularised membranes contract, and the tangential traction so produced is stabilised and consolidated by collagen synthesis. The tangential traction results initially in folding of the inner retinal layers (internal limiting membrane and nerve Þbre layer) and can then progress to traction retinal detachment.

Contraction of the neovascular membranes both anteroposteriorly and tangentially combined with shrinkage of the vitreous gel pulls the retina at its points of adhesion into the centre of the eye. Without a retinal hole to allow accumulation of subretinal ßuid, the retina detaches with a concave conÞguration. Two forces are acting on the retina, one the action of the RPE to keep the retina ßat and two the action of the shrinking vitreous and neovascular membranes pulling the retina centrally into the vitreous cavity.

During this process, the vitreous cortex often splits, leaving a thin layer on the retina that can be elevated during surgery to allow easier dissection of the Þbrotic neovascular membranes (Schwatz et al. 1996; Chu et al. 1996). The vitreous detachment on the inner surface of the vitreoschisis is taut and stretches from the vitreous base to the neovascular membranes and between the membranes. The areas of detachment surround neovascularisation on the retinal arcades and are often multifocal. Eventually the macula detaches severely reducing the visual acuity, whilst the

Fig. 12.20 The membranes in diabetic TRD usually form over the retinal vasculature, the optic disc and temporal to the macula encircling the macula. However, membranes can be seen anywhere in the retina

periphery remains ßat. The extent of tractional retinal detachment (TRD) varies from a single focus to large areas of the retina. Similarly and more important to the surgeon, the areas of adhesion of the neovascular membrane to the retina vary, often being most pronounced on the vascular arcades and around the optic disc.

12.2.4.3 Tractional Retinal Detachment

Additional surgical steps

Remove vitreous haemorrhage as above but retain any traction on the retina.

Create holes in the posterior hyaloid to allow easy access to the areas of retinal elevation and vitreoretinal adhesion.

Detect and elevate the posterior layer of any vitreoschisis.

Dissect the tractional membranes off the retina. Complete the removal of the vitreous.

Apply panretinal photocoagulation.

Where signiÞcant neovascular membranes exist or retinal detachment is present dissection by delamination of any membranes is required. The membranes are best removed in total (Ôen blocÕ) to prevent future reproliferation and subsequent detachment (Kakehashi 2002; Williams et al. 1989; Abrams and Williams 1987). The core of the vitreous is removed whilst retaining the taut peripheral gel thereby maintaining traction upon the membrane. A hole is made in the cortical gel to allow access of instruments to the retinal surface. The outer portion of the vitreous cortex on the retinal surface is then elevated to Þnd the plane of cleavage of the internal limiting membrane and posterior hyaloid membrane. The posterior hyaloid and the neovascular membranes are then dissected away from the retina to relieve traction and allow the retina to reattach. Modern cutters especially small gauge have oriÞces which are nearer the tip end of the cutter shaft.

Note: In less complex TRD, the membranes can be trimmed down by these cutters effectively shaving down the membrane until the retina is cleared to membrane rather than using scissors to dissect off the membrane.

Elevating the cortical gel and posterior hyaloid which is still attached to the surface of the retina is the key manoeuvre of the operation. Having made the hole in the elevated vitreous cortex, use the edge of the scissors to run along the slope of an area of TRD. may catch the posterior hyaloid and see it lift both outwards towards the equator and towards the TRD. Elevate the PHM up to the edge of the TRD and then use the plane between this and the retina to elevate the membranes. Alternatively, the correct plane can sometimes be found by starting in the macular area and working outwards towards the arcades.

Note: The PHM very often ends in the peripheral retina and does not often extend to the vitreous base in severe TRD.

In this plane, the membranes will separate much more easily. Cutting through cortical gel is much more difÞcult and will leave membrane on the retina, allowing later

Fig. 12.25 The membranes can cause traction and damage on the optic nerve, reducing visual recovery postoperatively

Fig. 12.26 A combination of rhegmatogenous and tractional retinal detachment may occur. Particular problems exist when the patient has a rhegmatogenous element in addition producing PVR. Other indicators of relative poor prognosis are subretinal haemorrhage and iris neovascularisation

reproliferation. Some of the membrane will lift off, but sites of adhesion that will not lift must be cut. Keep your visualisation to a maximum by trimming any elevated membrane with the cutter whilst maintaining some anteroposterior traction on the TRD. As with any membrane, work around points of adhesion, lifting the membrane around a difÞcult site before tackling it. Usually I will elevate and PHM around the TRD 360¡, if I can, before dissecting the area of TRD itself. When lifting the PHM, lift close to the edge of the TRD and then move tangentially out to elevate the PHM in the periphery.

Fig. 12.27 Occasionally an eye in which neovascularisation has been stabilised by laser will have inactive membrane overlying the macula

Fig. 12.28 Despite only minimal PRP, these membranes are stable perhaps indicating a Ôburnt outÕ retinopathy

Fig. 12.29 Try to work along a ridge of adhesion (a, often along a large blood vessel) rather than across it because the scissors can straddle the ridge (b) and keep away from the retina, and any forces (arrows) are applied to the relatively strong blood vessel (F arrow). Going across the ridge risks the tips of the scissors incising the retina (c and d), and the forces are applied to the weak retina on the slope of the ridge

a

c

b

F

d

F

a

b

a

b

Fig. 12.30 When using the posterior hyaloid to lift a membrane (e.g. TRD membrane) to look for pegs at site (b), stay close to the edge of the membrane. Lifting further away from the membrane requires a vertical movement to avoid traction at point (a) to see the pegs. This will also put a force on pegs deeper under the membrane which you cannot see. If you stay close to the membrane edge, a tangential motion is possible without undue force at point (a) and only applying force to pegs at the edge of the membrane

Normal

Fig. 12.31 The balancing act between pulling on an ERM and avoiding a retinal tear. In the normal eye, a large force is required before the retina tears, so that a relatively large force can be applied to pull off an ERM. In the ischaemic diabetic retina, a small force may tear the retina; therefore, only a small force can be applied to ERM to remove it

If using the PHM to lift the edge of the TRD, stay close to the TRD to achieve a large angle on the edge of the TRD without applying forces on the vitreous base.

Most TRDs are made up of peg attachments except: at the optic disc where a larger area of adhesion approximately ½ a disc area is seen. This will usually peel off the disc with some

Vitreous

Membrane

Retina

Fig. 12.32 It is important to dissect under the outer layer of a vitreoschisis which is easier than cutting through the vitreous to get to pegs of membranous attachment and avoids leaving vitreous on the retina

Fig. 12.33 The OCT of this patient shows the pegs of attachment between the membranes and the retina see 12.34.

cutting with scissors surprisingly easily though; be aware of the major blood vessels and vulnerability of the surface of the optic nerve head.

Where there is schitic retina, there can sometimes be a sheet of adhesion of the membrane to the retina.

Retinoschisis is an occasional feature in retina in TRD and is presumably due to splitting of the retina from traction. It may prevent ßattening of the retina at the end of the operation and application of laser. Often partial-thickness inner retinal holes are seen. Dissection of membrane is often difÞcult from the surface of the schitic area.

Fig. 12.34 See previous Þgure

Fig. 12.35 TRDs are characterised by a triangular-shaped elevation of the retina with attachment to the vitreous. The vitreous is usually immobile in these patients

Entry holes

Scissors

Fig. 12.36 Try to Þnd a route through the posterior hyaloid membrane to allow easy dissection of the membranes and insertion of your scissors underneath the posterior hyaloid membrane to aid dissection. These can be found conveniently in locations such as superotemporally or superonasally (a), so that you have access with right or left hand to the membranes or over the macula itself where it is possible to start centrally and work peripherally through the membranes (b). Once you have found your appropriate layer, 45o angle scissors can be used to dissect off the membrane from the retina. You must cut pegs of attachment of the membrane to the retina (c and d). Cutting, rather than pulling these apart, reduces bleeding and improves your postoperative re-bleed rate whilst minimising any chance of iatrogenic tears. Once you have made your access incisions in the posterior vitreous, work around the most severe membranes which are often on the arcades and disc, lifting the hyaloid around these sites, so that you can determine the most adherent foci before working down onto the most severe membranes themselves. Often these are found concentrated around blood vessels and the optic disc, but also can be found sporadically around the retina

a

Split in vitreous cortex

Retina

Subretinal space

b

Separation of vitreous from retina

Fig. 12.38 A peroperative picture shows a membrane which may tempt the surgeon into performing a dissection off only the anterior layer, but in fact, re-examination of the eye shows another layer indicated by the position of the scissors; a more posterior layer which is attached to the retina. This is the posterior hyaloid membrane and cortical remnants that make up the posterior leaf of the vitreoschisis. These must be elevated to Þnd the right plane for removal of the membranes

c

Separation of vitreous from retina

d

Fig. 12.37 (aÐd) Lift the vitreoschisis (a) on either side of the line of adhesion (b and c) before working along the line of adhesion (d) to detach the membrane

Fig. 12.39 Occasionally when dissections are difÞcult use bimanual surgery with illuminated forceps to hold membranes so that pegs can be seen and cut with scissors

Surgical Pearl of Wisdom

For diabetic tractional detachments: Sometimes it can be difÞcult (but necessary) to dissect and elevate midperipheral hyaloid in complex cases of diabetic tractional retinal detachments. Even when not necessary for visualisation, skilled scleral depression can be quite useful to relax the hyaloid and open a potential subhyaloid space. This can convert a challenging bimanual