may be mechanically removed in some cases.603 More frequently, an IOL exchange restores vision in symptomatic patients who have the potential for improvement.

Silicone may migrate from the vitreal cavity to extraocular sites. Subconjunctival and orbital

migration of silicone oil may occur through glaucoma drainage devices.604,605 Placement of the tube

inferiorly in the anterior chamber and avoiding anterior migration of silicone may prevent this complication. A rare, but serious complication of sili-

cone oil seen in ocular hypertensive eyes is dissection of silicone oil from the eye into the brain.606,607

Glaucomatous optic neuropathy may be requisite.608 Therefore, removal of silicone oil or evisceration/enucleation should be considered in a sightless, silicone-filled eye with elevated IOP even in the absence of pain.

Hypotony/phthisis: The DRVS reported the incidence of enucleation/phthisis/retrobulbar alcohol injection to be 12.3% in the early vitrectomy group compared with 9.1% in the deferral group.71 The most common causes of hypotony/phthisis include late effects of persistent retinal detachment, anterior

hyaloidal fibrovascular proliferation, and end-stage neovascular glaucoma.321,342,559 Management is

directed at cosmesis and pain control and may require topical medication, alcohol block, enucleation/evisceration, or scleral shell.609

Sympathetic ophthalmia: The potentially blinding complication of sympathetic ophthalmia is a rare complication of vitreoretinal surgery.610 Present findings include anterior chamber and vitreal inflammatory cells with variable posterior segment changes.611 The DRVS reported sympathetic ophthalmia in 1% of early vitrectomy group as opposed to 0.3% in the deferral group.71 These rates are higher than the expected incidence of 0.01–0.06% following vitrectomy surgery.612 The potential of blindness from sympathetic ophthalmia

underscores the importance of avoiding multiple surgeries in eyes with very poor prognosis.612,613

For those patients who do undergo vitrectomy, careful postoperative evaluation of the fellow eye is critical to diagnose sympathetic ophthalmia. With early detection and appropriate treatment, a good prognosis may be expected.614

Macular hole: Vitrectomy has rarely been associated with macular hole, both with and without

ILM peeling.358,360,362 This finding is not surprising given the strong vitreoretinal adherence in diabetic retinopathy.18 The presence of diabetic macular

edema may be a risk factor for the development of macular hole.358,360 Management is discussed under

the heading of vitrectomy indications.

9.4.7 General Outcome

Vitrectomy surgery generally improves the quality of life in diabetic patients, though the results are

largely dependent on the underlying retinal pathology.615,616 Improved vision-related quality of life

and visual function after vitrectomy depends on improvement in visual acuity and contrast sensitivity in both the better-seeing eye and the worse-see- ing eye.616 Visual acuity outcomes with vitrectomy have been reported earlier in this chapter as they relate to specific indications for surgery. There is an overall 67–86% rate of visual improvement after

vitrectomy for various complications of diabetic retinopathy.285,326 The overall 2-year visual acuity

results reported by the ETDRS (early vitrectomy group) and the DRVS are comparable: 24.5–28% were 20/40 or better, 17.1–20% were <20/40 to 20/ 100, 18.9–19.3% were <20/100 to 20/400, 3.6–8.0%

were <20/400 to 5/200, and 24.7–36% were <5/ 200.69,71 Over the 9-year study period of the

ETDRS, 2% of 7411 eyes suffered severe visual loss (<5/200). These eyes were enrolled with mild- to-severe NPDR and early PDR. The low rate of severe visual loss was attributed to close follow-up and timely laser/vitrectomy intervention. Risk factors for severe visual loss were high mean hemoglobin A1c and elevated cholesterol.615

A more recent, retrospective review of 340 eyes operated for a variety of complications of diabetic retinopathy showed an 86% incidence of improvement in vision. A final postoperative visual acuity of 20/40 or better was achieved in 60% of eyes.326

Other studies correlated postoperative vision inversely with severity of PDR. For example, better final vision was present in eyes with vitreous hemorrhage or good preoperative vision and worse outcome in eyes with retinal detachment.290 Preoperative risk factors for severe visual loss included pre-op vision <5/200, cataract, NVI/NVG, and