Glaucoma surgery can be classified as either cyclodestructive (reducing inflow) or filtering (increasing outflow). Filtration has traditionally been the procedure of first resort because of its efficacy and relative predictability, whereas ciliary destruction has been reserved for more refractory cases of glaucoma and in eyes which have little or no visual potential. Refractory glaucomas include neovascular glaucoma, post-traumatic glaucoma, glaucoma associated with aphakia, severe congenital/developmental glaucoma, post-retinal surgery glaucoma, glaucoma associated with penetrating keratoplasties, and glaucoma in eyes with scarred conjunctiva from surgery or disease processes.