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Viscosurgery in diabetic vitrectomy
  1. D McLeod
  1. University of Manchester, Manchester Royal Eye Hospital, Oxford Road, Manchester M13 9WH, UK;

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    Grigorian and colleagues recently recounted their experience of using viscosurgery to remove epiretinal membranes (ERMs) from eyes with proliferative diabetic retinopathy (PDR).1 They concluded that “viscodissection” (injection of Healon between the fibrovascular proliferations and the retina) is safe and is equally as effective as its non-use. On the contrary, their study shows that viscodissection is not cost effective (because of the costs of both the viscoelastic and the extra operating time), and confirms that the technique is inherently unsafe in PDR.2,3

    The use of Healon to aid dissection of fibroglial and fibrovascular ERMs during vitrectomy was introduced in the 1980s4 but was not widely adopted. Viscoelastic material squirting out from under the ERMs was “messy” and led to the formulation (in the 1990s) of yellow tinted Healon to aid its visualisation and simplify its removal5 and then Healon GV (viscosity 10 times that of Healon) for adherent diabetic ERMs.6 In 1984, we began undertaking “viscodelamination” in diabetic vitrectomy.2,7 This technique was primarily directed at stripping the posterior hyaloid membrane (PHM) from detached, ischaemic and atrophic peripheral retina. Viscodelamination was especially useful in combined tractional and rhegmatogenous retinal detachments (CTRD) with very limited non-rhegmatogenous posterior vitreous detachment (PVD) present. Because of the prohibitive cost of Healon, methylcellulose 1% was injected in the majority of eyes.

    To summarise our experience, stripping of the PHM usually proceeded uneventfully during slow pressurisation of the closed retrohyaloid compartment by viscoelastic, as did separation of any loosely adherent, sparsely vascularised ERMs that were contained within the peripheral vitreous cortex.2 In well photocoagulated eyes, the separation sometimes continued posteriorly, culminating in a complete PVD. In the case of more adherent fibrovascular ERMs, their “viscoelevation” sometimes occurred through stretching of the vascular and glial tent pegs connecting the ERMs to the retina. The PHM and ERMs could then be removed en bloc using the suction cutter. However, instead of stretching, the vascular connections between the ERM and the retina tended to be disrupted. Avulsion generally occurred at the point of greatest weakness at the origins of neovascular outgrowths from the retinal veins. Although correlating with ERM vascularity and with the density of neovascular outgrowths from the retina, ERM retinal adherence was unpredictable, and bleeding was ultimately an inevitable consequence of the perpendicular hydraulic forces necessary to effect peeling of more adherent ERMs. Fortunately, the bleeding from side punctures in the retinal veins was constrained by the viscoelastic (so called “haemorrhagic confinement”)2,8 and a high ambient intraocular pressure during the surgery. However, as was predictable in theory, but again unpredictable in practice, the hydraulic tension sometimes disrupted the retina ahead of, and instead of, peeling the ERMs. Furthermore, recurrent fibroglial membranes were sometimes observed later even in eyes where viscodelamination had proceeded uneventfully. This has been attributed to the difficulty in completely removing viscoelastic from the retinal surface, with preretinal retention of growth factors.2,3 Not for nothing is one viscoelastic mixture marketed as Viscoat. We had discontinued viscosurgery in PDR by 1988 in favour of purely mechanical methods that minimise ERM elevation.3

    Fifteen years on and Grigorian and colleagues have clearly come to a very different conclusion from ours despite reporting a considerable excess of iatrogenic posterior retinal breaks during, and recurrent detachment after, viscosurgery.1 By back calculation from their assiduously collected data, it appears that 20 posterior breaks were induced in 65 eyes undergoing viscodissection compared with four in 89 eyes having conventional surgery. This trend was confirmed in groups of eyes with pathology of similar (“relatively high”) complexity. Thus, there were 10 iatrogenic posterior breaks in 34 viscodissections in eyes in the range C4-6 compared with three in 26 conventional operations. (It is acknowledged that Grigorian et al state that the complexity score “does not account for the degree of adhesion,” neither was it “a good predictor of the amount of traction necessary to dissect a membrane.”) The intraoperative problems appear to have been reflected in the ultimate outcomes. After 6 months of follow up, for example, a detached retina was evident in seven of 43 eyes (16%) in the viscosurgery group compared with three of 58 eyes (5%) undergoing conventional surgery. Furthermore, although eyes with CTRD seemed to fare well whether or not Healon was used, this was not the case in eyes with tractional detachments (with or without vitreous haemorrhage). Six of 30 eyes (20%) had a detached retina 6 months after viscodissection compared with only two of 37 eyes (5%) after conventional surgery. Indeed, most of the data favoured conventional surgery. Lower viscosity Healon was proposed as a future means of reducing the frequency of iatrogenic breaks, but this is unlikely to be helpful in their attempt to achieve the impossible—that is, a worthwhile increase in the ease and speed of ERM removal without an unacceptable added risk of retinal haemorrhage, tears, and scarring. Better by far would be to avoid viscoelastics altogether.