Transscleral drainage of subretinal fluid revisited.

Fashioning a puncture hole through the sciera, choroid, Bruch's membrane, and retinal pigment epithelium for external drainage of subretinal fluid (SRF) may not be conceptually challenging, but the multiplicity of reported methods attests to the problems experienced in achieving the desired end simply and without extraocular egress of the retina or intraocular complications. The latter include retinal perforation and choroidal haemorrhage with subretinal or suprachoroidal spread. Until recently, the relative efficacy and safety of these various SRF drainage procedures had seldom been investigated through clinical trials, perhaps reflecting the variability of presentation of rhegmatogenous retinal detachments and the influence of the charismatic schools of vitreoretinal surgery in shaping opinions. Incremental deepening of a 2-4 mm long scleral incision1-l0 permits choroidal exposure, visualisation and possible coagulation before choroidotomy, but necessarily invokes a risk of inadvertent choroidal puncture, retinal incarceration, and potential reopening of the sclerotomy at reoperation. By contrast, the much smaller sclerochoroidal opening after hypodermic needle or suture needle drainagell-13 virtually eliminates the risk of incarceration while inviting choroidal haemorrhage unless the intraocular pressure is maintained high enough and long enough for haemostasis to become established. After scleral cutdown, the choroid can be coagulated by cautery or diathermy256 before mechanical puncture; alternatively, choroidal vaporisation without intrusion using either diathermy6 or an argon laser (via a fibreoptic probe or the indirect laser delivery system)7-10 aims to reduce the risk ofhaemorrhage, retinal perforation, or failure of drainage. Although initial lower energy, longer duration coagulation of the choroid tends to reduce choroidal haemorrhage on subsequent vaporisation,269 it also lowers the rate of first time success of SRF drainage9 while retinal perforation remains a possibility.89 The risk of haemorrhagic complications is also felt to reflect the site of SRF drainage that is, with a reduced risk at the watershed of vortex vein territories near the horizontal (as opposed to the vertical) recti,4 5 14 and the sequence of individual retinal procedures that is, with a putative benefit from drainage before cryotherapy.4 13 14 However, few of these nostrums have been supported by substantive evidence through clinical trials. Prospective studies tend to be more objective than retrospective studies, a healthy scepticism ensuing when a retrospective search of patient records is reported to reveal