Dear Editor

We thank Professor McLeod for his careful review [1] of our paper, “Epiretinal membrane removal in diabetic eyes: comparison of viscodissection with conventional methods of membrane peeling” [2] and appreciate the opportunity to address some of the issues he has raised.

Professor McLeod points out that our conclusion, i.e. viscodissection and conventional methods of membrane peeling (pick and scissors dissection) are equally effective, was made despite an excess of iatrogenic posterior retinal breaks during, and recurrent retinal detachment after, viscodissection. He notes that 20 posterior breaks were induced in 65 eyes that underwent viscodissection, and only four posterior breaks were induced in 89 eyes in non-viscodissection group. Our conclusion is based entirely on a careful statistical analysis of the data. We did not find any statistically significant difference in the incidence of iatrogenic posterior retinal breaks between the visco- and non-viscodissection groups based on the type of the treatment (p=0.4) or the case complexity score (p=0.1). Similarly, among a subgroup of eyes with high complexity scores (CS=4-6), there was no statistically significant difference in the incidence of retinal breaks based on the type of the treatment (p=0.66).[2]

Professor McLeod notes that after a six-month follow-up, the retina was detached in 16% of eyes in viscodissection group vs. 5% in non- viscodissection group. Specifically, he points out that among the eyes with tractional detachment with or without vitreous hemorrhage (TRD±VH), six (20%) of 30 eyes had retinal detachment in the viscodissection group vs. two (5%) of 37 eyes in non-viscodissection group after 6 months follow -up. We believe that higher incidence of retinal detachments is related to the fact that eyes in viscodissection group had more complex anatomy than eyes in non-viscodissection group. Statistical analysis revealed that the cases done by viscodissection were significantly more complex than those done without viscodissection (p <_0.0001.2 furthermore="furthermore" among="among" patients="patients" with="with" trdvh="trdvh" at="at" least="least" six="six" months="months" follow-up="follow-up" the="the" analysis="analysis" did="did" not="not" reveal="reveal" a="a" statistically="statistically" significant="significant" difference="difference" in="in" incidence="incidence" of="of" retinal="retinal" detachments="detachments" between="between" visco-="visco-" vs.="vs." non-viscodissection="non-viscodissection" treatments="treatments" p="p"> We agree with Professor McLeod that operating time for viscodissection cases is longer than for nonviscodissection cases.[2] We believe the operating time is longer due to the fact that the viscodissection cases were more complex.

We disagree with Professor McLeod's concern that viscodissection is inherently unsafe in eyes with proliferative diabetic retinopathy. This study compared a group of eyes that underwent membrane peeling using viscodissection with a group of eyes that underwent membrane peeling without viscodissection. We did not find any statistically significant difference in the outcomes between two groups (i.e. visual acuity, retinal reattachment rate, incidence of retinal breaks).

We pointed out that one can draw only limited conclusions from this study due to its retrospective, non-randomized design.[2] The data from the study indicate, however, that viscodissection can be used for the management of complex retinal detachments in eyes with proliferative diabetic retinopathy. Statistical analysis of the results indicates the differences in outcome for visco- vs. non-viscodissection cases that were detected are most likely due to chance alone. In other words, viscodissection and conventional pick and scissors dissection without viscodissection appear to be equally effective among patients with the reported case complexity for the group of surgeons in question.

References

(1) McLeod D. Viscosurgery in diabetic vitrectomy [electonic response to Grigorian et al. Epiretinal membrane removal in diabetic eyes: comparison of viscodissection with conventional methods of membrane peeling] bjophthalmol.com 2003 http://bjo.bmjjournals.com/cgi/eletters/87/6/737#163

(2) Grigorian RA, A Castellarin A, Fegan R, Seery C, Del Priore LV, Von Hagen S, Zarbin MA. Epiretinal membrane removal in diabetic eyes: comparison of viscodissection with conventional methods of membrane peeling. Br J Ophthalmol 2003;87:737-741.

Dear Editor

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 (owing to 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 1980s [4] but wasn’t 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 removal [5] and then Healon GV (of 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 tentpegs 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 4 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 3 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 follow-up, for example, a detached retina was evident in 7 of 43 eyes (16%) in the viscosurgery group compared with 3 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 2 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 trying to achieve the impossible –ie 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.

References

(1) Grigorian RA et al. Epiretinal membrane removal in diabetic eyes: comparison of viscodissection with conventional methods of membrane peeling. Br J Ophthalmol 2003; 87:737-741.

(2) McLeod D, James CR. Viscodelamination at the vitreoretinal juncture in severe diabetic eye disease. Br J Ophthalmol 1988; 72:413-419.

(3) Charles S. Techniques and tools for dissection of epiretinal membranes. Graefe’s Arch Clin Exp Ophthalmol 2003; 241:347-352.

(4) Stenkula S et al. The use of sodium-hyaluronate (Healon) in the treatment of retinal detachment. Ophthalmic Surg 1981;12:435-43.

(5) Stenkula S et al. Healon yellow as a surgical tool in maneuvering intraocular tissues. Ophthalmic Surg 1992; 23:708-710.

(6) Crafoord S, Stenkula S. Healon GV in posterior segment surgery. Acta Ophthalmol (Copenh) 1993; 71:560-561.

(7) Barry PJ et al. Reparative epiretinal fibrosis after diabetic vitrectomy. Trans Ophthalmol Soc UK 1985; 104:285-296.

(8) Folk JC et al. Sodium hyaluronate (Healon) in closed vitrectomy. Ophthalmic Surg 1986; 17:299-306.