Silicone oil in diabetic vitrectomy

Castellarin and colleagues¹ recount their recent experience of infusing silicone oil in a small series of patients with advanced diabetic eye disease, either during primary vitrectomy (12 eyes) or after earlier surgery had failed (11 eyes). They compare their results with previous reports and conclude that silicone oil remains a useful adjunct in diabetic vitrectomy. However, their conclusions and historical comparisons are open to question.

Silicone oil was first used in primary diabetic vitrectomy in an era (1979–84) before the introduction of endolaser and the Landers’ double concave lens for phakic fluid:air exchange.^2–4 Dealing with large or multiple posteriorly located breaks (whether pre-existing or iatrogenic) was problematic, and direct fluid:silicone oil exchange (by virtue of the optical advantages of oil over air in the phakic eye) provided a surgical escape route, obviating the need for lensectomy. Furthermore, the clarity of the media immediately postoperatively facilitated the slit lamp delivery of focal laser in order to seal retinal breaks that had been closed by the internal tamponade and, in addition, the application of scatter laser to reattached, untreated, ischaemic retina that had undergone deturgescence, in part through the “waterproofing” effect of silicone oil.^3,4 All being well, the silicone oil could then be removed shortly thereafter, and some eyes that would undoubtedly have been lost were saved by the intervention of silicone oil in this way. Often, however, there were considerable associated problems, not least the rapid development of reparative epiretinal fibrosis whereby the retina redetached under tangential traction and/or from reopening of retinal breaks.^2–6 Sometimes huge areas of retinal disintegration eventually developed.^5,7 The fibroglial epiretinal proliferation appeared (both clinically and pathologically) to be particularly induced by clotted blood trapped between the silicone oil and the retinal surface or, ironically, by fibrin released as a result of the extensive scatter laser that was often needed to prevent highly vascularised membranes from reproliferating behind the silicone oil.^4,5,8,9

It was hoped that the so called “compartmentalisation” of the eye by silicone oil (to which the retro-silicone oil neovascularisation was attributed) might in turn result in prevention or reversal of rubeosis iridis through its putative barrier effect against anterior diffusion of angiogenic substances derived from the ischaemic retina.^3–8 Paradoxically, eyes with successful retinal reattachment (albeit with unabated ischaemia) often underwent rapid development or progression of iris neovascularisation,^3,8 while those with failed surgery from postoperative rhegmatogenous recurrence of retinal detachment (and therefore eyes with an exaggerated angiogenic drive) had evidence of protection from rubeotic phthisis, at least in the short term.³ Perhaps naively it was postulated that rhegmatogenous confinement of the redetachment by intravitreal silicone oil (and the consequent 100% oil filling of the shrinking vitreous cavity) might allow an effective obstruction to anterior molecular diffusion to be established in these failed cases.³ Others had planned from the outset to employ silicone oil in their surgical protocol, not least for those diabetic eyes wherein earlier vitrectomy had been unsuccessful as a consequence of retinal redetachment^4,10,11 or recurrent vitreous cavity haemorrhages.⁴ However, whether used during primary diabetic vitrectomy or secondarily, whether unpremeditated or planned, and whether infused by direct fluid:oil exchange or sequential fluid:air and air:oil exchanges, the possibility of silicone oil limiting rubeosis and maintaining macular attachment despite peripheral retinal redetachment was always welcome, even if surgical “success” (that is, retinal attachment through 360 degrees) had strictly been denied.^2–4,8,12

Nowadays, posterior retinal breaks and retinectomies can generally be managed successfully by employing wide angle viewing systems, heavy liquids, endolaser, and long acting gases. However, silicone oil continues to be infused during diabetic vitrectomy despite the attendant posterior segment and anterior segment complications that have been only partially mitigated by the improved quality of the silicone oil. The important question that thus arises is: what is the appropriate use of silicone oil in the diabetic eye in the modern era? Where retinal breaks might be closed just as readily using gas tamponade, or where rubeosis iridis might be reversed or prevented by retinal reattachment and/or a sufficiency of scatter laser photocoagulation, the use of silicone oil might be described fairly as “gratuitous.” Exceptions might include anticipated posturing difficulties³ or the need for early visual rehabilitation in one eyed patients.⁴ However, recent reports documenting the use of silicone oil in diabetic vitrectomy have failed to provide clear criteria or explanations regarding case selection.^1,12,13 Only seven of the 23 eyes in Castellarin and colleagues’ series, for example, had retinal breaks (two pre-existing, four iatrogenic, and one retinectomy), so the need for prolonged internal break tamponade was presumably not an issue in the majority of their eyes. More information is needed on the rationale for silicone oil infusion (not just the overall indications for surgery) in the remaining eyes in order to enable the potential benefits of this surgical adjunct to be assessed at this time. Furthermore, surgical success can really only be judged after a minimum of 6 months from the last vitreoretinal procedure,^{3,4,8,10–12} and that judgment should preferably include consideration of whether the silicone oil has been removed and the status of the fellow eye.¹⁴ The fact that 10 of the 23 eyes in Castellarin’s series were followed for only 1 or 2 months was thus a further serious limitation of their study.¹

Infusion of silicone oil can be a most beguiling option during the closed microsurgical management of the stricken diabetic eye but, as mentioned, complications are prone to accumulate with time. Distinguishing the gratuitous from the virtuous use of silicone oil can be problematic, and equally it may be difficult to define the line between a surgeon’s infusing silicone oil in anticipation of eventual surgical failure and such infusion representing his/her unstated admission that surgical failure has occurred already. All these issues need to be borne in mind when making historical comparisons between case series and in defining the place in history for silicone oil in diabetic vitrectomy.