Relationship Between Eye Pressure and Ganglion Cell Function in Eyes Receiving Latanoprost Versus Placebo

Inclusion Criteria: Inclusion Criteria - OHT: * Ocular hypertension defined as an IOP ≥ 24 mm Hg and ≤ 32 mm Hg in one eye and IOP ≥ 22 mm Hg and ≤ 32 mm Hg in the fellow eye * Normal optic disc * Normal visual field defined as follows: * Mean Deviation (MD) or Pattern Standard Deviation (PSD) of p\>5% * Normal Glaucoma Hemifield Test (GHT) * Reliable visual field exam (less than 33% false positives or false negatives, and less than 20% fixation losses) Inclusion Criteria - POAG: * Glaucomatous visual field loss defined as a CPSD (p \< 0.05), or GHT (p \< 1%) outside normal limits with consistent with ONH or NFL defect * Early visual field loss defined as MD ≤ -6.0 dB * Untreated IOP ≤ 32 mmHg * ONH or NFL defect defined as either inter-eye CDR asymmetry \> 0.2, rim thinning or notching, or NFL bundle defect visible on slitlamp biomicroscopy and stereo color fundus photography Exclusion Criteria: Exclusion Criteria - OHT: * Best-corrected visual acuity less than 20/40 either eye * Abnormal or unreliable VF * Untreated IOP \> 32 mmHg * Age \< 18 or \>85 years * Refractive error of \> +3.00 D or \< -7.00 D * Previous intraocular surgery except for uncomplicated cataract extraction with posterior chamber intraocular lens implantation * Need for chronic ocular or systemic corticosteroid use * Narrow/closed angle (gonioscopy must show 75% or more of the angle to be Grade 2 or more by Shaffer's grading system) * Diabetic retinopathy * Other diseases that may cause VF loss or optic disc abnormalities * Life-threatening or debilitating illness making it unlikely patient could successfully complete the study * Inability to clinically view or photograph the optic discs due to media opacity or poorly dilating pupil * Refusal of informed consent or of commitment to the full length of the study * Contraindication to latanoprost or placebo vehicle Exclusion criteria - POAG: * Best-corrected visual acuity less than 20/40 * Untreated IOP \> 32 mmHg * Age \< 18 or \>85 years * Refractive error of \> +3.00 D or \< -7.00 D * Previous intraocular surgery except for uncomplicated cataract extraction with posterior chamber intraocular lens implantation * Diabetic retinopathy * 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 could successfully complete the study. * Refusal of informed consent or of commitment to the full length of the study * Contraindication to latanoprost or placebo vehicle