Monitoring intraocular pressure (IOP) is a critically important part of glaucoma management; however, clinical tonometry predominantly involves sitting postures and is unable to detect variations in response to posture changes, muscular effort, deep respirations and during a wide range of activities, such as playing high wind-resistance instruments and wearing swimming goggles in addition to eye touching and rubbing. For example, the usefulness of 24-hour tonometric phasing may be increased, if nocturnal assessments included side and prone sleeping postures rather than being limited to supine posture tonometry. Continuous monitoring of IOP, which allows unrestricted involvement in a full range of sleep and non-sleep IOP elevating activities would provide an ideal method of quantifying the frequency, duration and degree of episodes of elevation in addition to physiological and pathological circadian rhythmic variations due to treatment. Apart from the degree of exposure to episodes of elevation of IOP, genetic influences and family history of glaucoma, other factors which are or could be associated with increased susceptibility to develop or progress glaucomatous pathology include age, frailty, race, type and degree of refractive error, systemic hypotension and hypertension, vasospasm, migraine, pigmentary dispersion syndrome, pseudoexfoliation syndrome, obstructive sleep apnoea syndrome, diabetes as well as medication interactions and side effects. Such information, when combined with all details relating to episodes of elevation of IOP, appears likely to be a strong basis for the detection, diagnosis and treatment of glaucoma. This review examines the limitations of methods of longitudinal monitoring of IOP with reference to their validity and the varying degrees of invasiveness involved. Also mentioned is the potential value of knowing the frequency, duration and level of variations of optic nerve subarachnoid space pressure, as the interaction of such changes with IOP and their potential influence on the lamina cribrosa, may help determine pathological significance.