In general, an association exists between the ocular pressure level and the future development of glaucomatous visual function loss. Using the ocular pressure reading, the task of searching for individuals who are likely to develop glaucomatous visual function loss can be limited. Identification of the individual who is destined to develop glaucomatous field defect cannot be made on the basis of tonometric and tonographic values with any practical degree or precision as to warrant the diagnosis or the therapeutic intervention for glaucoma prior to the onset of visual field defect, nor can the definite diagnosis of glaucoma be made in the individual subject prior to the demonstration of a characteristic involvement of visual function. Skillful thorough examination of the central visual field must be the cornerstone of any attempt at early detection of glaucoma.