Phacoemulsification has become the most commonly used procedure in cataract surgery owing to the development of new devices and surgical techniques; however, corneal endothelial damage still represents a serious complication. Although several factors are known to cause corneal endothelial damage, effects of irrigating pressure and temperature rise in the anterior chamber should also be considered. Furthermore, free radical formation is another important harmful factor. Ultrasound in aqueous solution induces cavitation, which results in the formation of hydroxyl free radicals that damage the corneal endothelium. The best protection is the use of ophthalmic viscosurgical devices. In addition, the use of H2 gas as an anti-free radical agent in the irrigating solution is discussed. At present, corneal endothelial injury is usually assessed using the limited range of specular microscopy. Corneal volume might be a new parameter with which to assess total corneal endothelial function.