Eye Pressure Lowering Surgery

The purpose of this study is to determine if lowering the pressure inside the eye improves blood flow to the eye.

Inclusion Criteria: * Subjects diagnosed with perimetric open angle glaucoma or chronic angle closure glaucoma. * Subjects scheduled to undergo trabeculectomy or tube shunt surgery Exclusion Criteria: * Best-corrected visual acuity less than 20/40 * Age \< 18 or \>85 years * Refractive error of \> +3.00 D or \< -7.00 D * Previous vision correction surgery such as Laser-Assisted in situ Keratomileusis (LASIK) or Photorefractive Keratectomy (PRK) * Previous intraocular surgery except for uncomplicated cataract extraction with posterior chamber intraocular lens implantation * Diabetic retinopathy * History of heart failure, myocardial infarction, transient ischemic attack or stroke * Other diseases that may cause VF loss or optic disc abnormalities * Inability to clinically view or photograph the optic discs due to media opacity or poorly dilating pupil * Inability to perform reliably on automated VF testing * Life-threatening or debilitating illness making it unlikely patient will successfully complete the study. * Refusal of informed consent or of commitment to the full length of the study