POSTOPERATIVE INTRAOCULAR-PRESSURE ABNORMALITIES IN THE SILICONE STUDY - SILICONE STUDY REPORT 4

Background: Chronically abnormal intraocular pressure (IOP) may follow surgery for proliferative vitreoretinopathy (PVR), using either long- acting gas or silicone oil tamponade. Its prevalence and clinical sign ificance are unclear. Methods: In the Silicone Study, 241 eyes with se vere (greater-than-or-equal-to C-3) PVR were treated with vitrectomy, randomized to perfluoropropane gas (C3F8) or silicone oil, and followe d for 6 months or longer. Chronic IOP abnormalities, based on findings at two consecutive or any three postoperative visits, were defined as (1) low IOP (hypotony), 5 mmHg or less, or (2) elevated IOP, more tha n 25 mmHg. Results. Eleven (5%) eyes had chronically elevated IOP and 58 (24%) had chronic hypotony. Chronically elevated IOP was more preva lent in eyes randomized to silicone oil than in those randomized to C3 F8 gas (8% versus 2%; P < 0.05). Chronic hypotony was (1) more prevale nt in eyes randomized to C3F8 gas than in those randomized to silicone oil (31 % versus 18%; P < 0.05); (2) more prevalent in eyes with anat omic failure (48% versus 16%; P < 0.01); and (3) correlated with poor postoperative vision (P < 0.0001), corneal opacity (P < 0.001), and re tinal detachment (P < 0.001). Factors prognostic of chronic hypotony i ncluded preoperative hypotony (P < 0.01), diffuse contraction of the r etina anterior to the equator (P < 0.01), rubeosis (P = 0.02), and lar ge retinal breaks (P = 0.02). In a multivariate analysis, diffuse cont raction of the retina anterior to the equator remained an independent factor prognostic of chronic hypotony (odds ratio = 4.2), regardless o f whether the retina was attached postoperatively. Conclusion. Intraoc ular pressure abnormalities are a common postoperative complication in eyes with PVR, and may occur with either C3F8 gas or with silicone oi l. The presence of diffuse contraction of the retina anterior to the e quator should alert the vitrectomy surgeon that the eye is likely to b e hypotonus postoperatively.