Glaucoma is the second leading cause of blindness worldwide. In the United States, approximately 2.5 million Americans are affected by this potentially blinding eye disease. Optical coherence tomography is the only non-invasive imaging technique allowing high-resolution cross-sectional imaging of the human retina. Since glaucoma causes thinning of the retinal nerve fiber layer prior to initial loss of vision, optical coherence tomograhy (which can measure the nerve fiber layer thickness) could enable early detection of glaucoma prior to any permanent loss of vision. This earlier detection would enable earlier treatment to prevent permanent loss of vision. Since glaucoma also causes progressive nerve fiber layer thinning prior to further loss of vision, optical coherence tomography could enable earlier detection of glaucomatous disease progression prior to further permanent loss of vision, enabling more aggressive preventive treatment. Current clinical techniques only allow diagnosis of glaucomatous loss of vision after up to half of the retinal ganglion cells are permanently lost. The overall goal of this research is A) to develop a video rate Optical Coherence Tomography (OCT) system for 3 dimensional high resolution imaging of the human retina and the retinal nerve fiber layer (RNFL), B) to determine the resolution and reproducibility of in vivo retinal nerve fiber layer thickness determination with video rate OCT in normal and glaucoma subjects, C) to correlate in vivo human OCT images with histology of the same eye.