Although use of the Honan intraocular pressure reducer is believed to be clinically safe and effective in reducing IOP and the risk of vitreous loss, the IOPs achieved during application of the device have not been directly measured. Intraocular pressure dynamics in ten eyes of five patients were measured shortly after death, using a pressure transducer within the anterior chamber as the Honan device was applied. Pressures were measured again after enucleation. The peak IOPs produced in eyes in situ were much lower than in the same eyes after enucleation. The peak IOP increased as the initial IOP was raised. The Honan device would appear to be safe for eyes undergoing routine anterior segment surgery, but the pressures that may be generated in hypertensive eyes (IOP greater than or equal to 35 mm Hg) might put these eyes at risk for vascular occlusion.