A study to determine whether a patient's range of vision test results improve after their eye pressure is lowered by 30% or more by testing on a new machine called the Accumap and how to learn how much the Accumap's results change from one test to another within the same person.

The investigators believe that Multifocal VEP readings (Accumap)(and therefore visual function and ganglion cell function) improve after acutely lowering intraocular pressure.

Accumap testing will be performed before and two to three hours after treatment is initiated to lower IOP. In eye that have bilateral treatment, one eye will be assigned randomly to the study. The mean multifocal objective perimetry amplitude will be compared before and after IOP reduction. Also, the mean amplitudes of five circumferential zones will be compared before and after IOP lowering. Visual field testing and HRT testing will be performed before and after treatment as well if possible. Paired t-tests will be performed no pre-and post-treatment mean MOP amplitude values and circumferential zones to determine statistical significance. A second group of patients whose pressures will not be lowered will also be tested with Accumap at baseline and two hours afterwards, in order to examine reproducibility of mean MOP amplitude and mean circumferential amplitude. HVF and HRT testing will also be obtained on thes patients when possible.

Inclusion Criteria:

• Consecutive patients seen that have their intraocular pressures lowered by at least 30% over the course of two hours.

Exclusion Criteria:

• Recent (within 6 weeks) intraocular surgery
• Visual acuity worse than 20/40
• Pathology unrelated to glaucoma (retinal disease, stroke, brain tumor, etc) associated with visual field defect
• Prior corneal transplant, corneal edema, or corneal diseases such as keratoconus or dense scarring

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