A process is disclosed for liquefying the vitreous humor of an eye. The process includes the steps of delivering plasmin into the vitreous of the eye and incubating the vitreous and plasmin together for a period of time. Plasmin may be introduced through injection or a sustained release device. Plasmin may be used to treat a pathological condition of the eye such as diabetic retinopathy, macular hole, macular pucker, intraocular infection, foreign intraocular material and retinal detachment.