Drainage of subretinal fluid is performed at a site determined by the configuration of the retinal detachment. Sufficient subretinal fluid is necessary to allows safe drainage. Factors considered in the selection of a drainage site include (1) the distribution of subretinal fluid when the eye is in a position at which drainage will be performed, (2) the location and size of the retinal break(s), (3) the location and configuration of the buckle, (4) the vascularity of the choroid, (5) features of vitreoretinal and epiretinal membrane traction, and (6) the ease of exposure of the proposed drainage site. The optimal locations for drainage are usually just above or below the lateral rectus muscle, because major choroidal vessels are avoided, and exposure of sclera is excellent. Choroidal vessels are also avoided by draining on either side of the three remaining rectus muscles, but exposure is frequently more difficult. If possible, drainage is usually performed some distance from retinal breaks, especially large retinal breaks, so that passage of vitreous through the break(s) and out of the eye can be minimized. The scleral depression effect provided by the buckle or by a cotton tipped applicator can help prevent this occurrence. In unusual situations in which a large buckling effect is required and very little subretinal fluid exists, drainage can be performed immediately beneath a large tear to allow both subretinal and intravitreal fluids to exit the globe. Drainage is performed prior to tightening the scleral buckling elements onto the eye, since a high intraocular pressure at the time of drainage increases the risk of complications. A site is usually selected at or slightly anterior to the equator, and a location that will ultimately be closed by the exoplant is preferred (usually in the bed of the exoplant). This avoids the need for a preplaced suture at the sclerotomy site, and it facilitates subsequent management of drainage complications, as noted later. In the situation in which drainage cannot be performed optimally at a site intended to be covered by the buckle, a preplaced suture is employed to close the scleral incision following drainage. This suture is placed after the sclera incision is made but before the choroid is penetrated. A 3-4 mm incision through sclera is performed so that the center of the sclerotomy will be at the appropriate location. All scleral fibers are carefully divided until subtle prolapse of uveal tissue is observed. The choroid may then be closely inspected for prominent choroidal vessels. If large visible vessels cannot be avoided during planned penetration, a second site nearby is selected, and another scleral incision is performed. If the area of exposed choroid is free of prominent vessels, it is sometimes treated lightly with a flat diathermy probe. This causes minimal retraction of the edges of the sclera to improve visualization, and it may reduce the risk of hemorrhage. All significant traction upon the eye is eliminated to reduce intraocular pressure as much as possible. The choroid is then penetrated with a sharp-tipped conical penetrating diathermy electrode or suture needle. Modest pressure is used to insert the device perpendicular to the surface of the sclera until the subretinal space is entered. If the conical diathermy electrode is used, this event is usually heralded by a sudden subtle "pop" which is usually perceived by touch or observation. Because of the tapered shape of the electrode, significant amounts of subretinal fluid do not exit the eye until this device is very slowly withdrawn from the eye. The penetrating diathermy electrode is relatively blunt, compared to a suture needle, and penetration of a soft eye with a congested choroid may be somewhat difficult. This is managed by modest elevation of intraocular pressure with traction upon the muscle fixation sutures. An oblique or tangential path of penetration is recommended by some authors to avoid perforating the retina, but this can result in a flap valve of the choroid, which can limit drainage. If a proper drainage site has been selected, penetration of the retina with the tapered diathermy is exceptionally rare, because it is removed prior to the release of significant amounts of subretinal fluid. Lasers have also been employed to drain subretinal fluid, but the expense and time required to use them do not appear to be balanced by a significant reduction in the rate of complications. As the globe softens during drainage, intraocular pressure is very slowly increased to encourage further drainage and to avoid complications associated with hypotony. If a large tear is present, the sclera or the buckle and sclera overlying the break are indented with a cotton applicator. This maintains intraocular pressure and inhibits passage of intravitreal fluid to the subretinal space. Pressure can also be increased by placing applicators on either side of the sclerotomy site and gently pushing them toward the center of the eye, and these maneuvers also tend to keep the sclerotomy open. Relatively normal intraocular pressure can also be maintained by indenting the sclera at a location far from the sclerotomy site with numbers of cotton applicators. The drainage site is not touched as long as fluid flows through it. Sudden and significant increases in intraocular pressure are avoided to reduce chances of incarceration of the retina in the sclerotomy, and any sudden cessation of drainage requires immediate closure of the sclerotomy and internal examination of the sclerotomy site with the indirect ophthalmoscope. The appearance of pigment granules suspended in the draining subretinal fluid usually indicates that the last of the subretinal fluid is exiting the eye. When drainage ceases, the sclerotomy site is closed by temporarily tying the sutures over an exoplant or by pulling together the ends of an encircling band. If the locations of buckling material will not adequately close the sclerotomy, the scleral incision is closed with the preplaced suture prior to significant elevation of intraocular pressure with the buckle. The eye is quickly inspected following closure of the sclerotomy site and a preliminary adjustment of the scleral buckle. The site of drainage is first evaluated for signs of subretinal bleeding, retinal incarceration, and iatrogenic hole formation, and management of these relatively unusual introperative problems is briefly discussed later. The amount of persistent subretinal fluid is then determined, and the need for further drainage is considered. Significant subretinal fluid is allowed to persist if the optimal amount of buckling nearly closes the retinal break(s). If drainage of additional subretinal fluid is required, the initial sclerotomy site must be closely evaluated with mobile scleral depression, in which a cotton-tipped applicator is rolled circumferentially beneath the area of drainage. If the pigment epithelium is clearly not in contact with the retina, the sclerotomy site can be reopened by reducing intraocular pressure and/or removing the portion of the exoplant that covers the scleral incision. Additional drainage usually occurs spontaneously, or it can be initiated by gently manipulating the edges of the sclerotomy with applicators or a forceps. In some cases, particularly those with exceptionally viscous subretinal fluid, the retina may flatten completely at the site of the sclerotomy while large amounts of subretinal fluid persist elsewhere. In this situation, additional sclerotomies must be performed if additional drainage is required to produce an adequate buckling effect. An alternative and increasingly popular method of draining subretinal fluid is to insert a small 25-30-gauge needle into the subretinal space using direct visualization with the indirect ophthalmoscope or operating microscope. The needle is usually attached to a tuberculin syringe from which the plunger has been removed. Digital pressure is exerted on the eye or significant intraocular pressure is maintained with traction sutures as the subretinal fluid passively exits the eye. The needle is dynamically positioned to remain within subretinal fluid, and it is slowly retracted as the retina approximates its tip.
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