Primary open angle glaucoma is the second and leading cause for visual damage worldwide. What is lost because of glaucomatous damage cannot be restored by any mean. Its early detection is the most important factor in prevention of such a damage. The current book will highlight the different aspect of glaucomatous damage including; functional visual field damage, morphological optic nerve head and retinal nerve fiber layer damage and changes of the blood flow in the optic nerve head and retinal nerve fiber layer in definite and suspected glaucoma patients and ocular hypertensives as well. The relationship between different modalities of visual field testing (SAP, SWAP and FDT) will be described, in addition standard photography and OCT changes will be compared for the ability to detect early glaucoma. Blood flow changes at the optic nerve head will be compared in both POAG, OHT and glaucoma suspects. The book will clarify which aspect of glaucomatous damage precede the other in different stages of glaucoma and whether is it necessary to test the different aspects of glaucoma damage in order to reach a definite diagnosis.