Low Tension Glaucoma

59-year-old woman has a history of glaucoma dating back to 1990. She had trabeculectomy in the left eye in 1998 and then persisted to lose vision despite normal intraocular pressures from low-tension glaucoma in the left eye. She is now on Cosopt and Travatan in both eyes.
Vision OD is 20/20, OS is 20/16. IOP: OD 9, OS 6.