Postoperative intraocular pressure abnormalities in the Silicone Study. Silicone Study Report 4

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 significance are unclear.

In the Silicone Study, 241 eyes with severe (> or = C-3) PVR were treated with vitrectomy, randomized to perfluoropropane gas (C3F8) or silicone oil, and followed 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 than 25 mmHg.

Eleven (5%) eyes had chronically elevated IOP and 58 (24%) had chronic hypotony. Chronically elevated IOP was more prevalent in eyes randomized to silicone oil than in those randomized to C3F8 gas (8% versus 2%; P < 0.05). Chronic hypotony was (1) more prevalent 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 anatomic failure (48% versus 16%; P < 0.01); and (3) correlated with poor postoperative vision (P < 0.0001), corneal opacity (P < 0.001), and retinal detachment (P < 0.001). Factors prognostic of chronic hyotony included preoperative hypotony (P < 0.01), diffuse contraction of the retina anterior to the equator (P < 0.01), rubeosis (P = 0.02), and large retinal breaks (P = 0.02). In a multivariate analysis, diffuse contraction of the retina anterior to the equator remained an independent factor prognostic of chronic hypotony (odds ratio = 4.2), regardless of whether the retina was attached postoperatively.

Intraocular pressure abnormalities are a common postoperative complication in eyes with PVR, and may occur with either C3F8 gas or with silicone oil. The presence of diffuse contraction of the retina anterior to the equator should alert the vitrectomy surgeon that the eye is likely to be hypotonus postoperatively.