The intraocular pressure is still a very important, of not the most important factor in glaucoma. This is because it is the only factor for which proof has been accumulated that it has a direct relationship with glaucomatous damage. In NPG the influence of the intraocular pressure alone is doubtful, but as an accessory risk factor deteriming the perfusion pressure it may very probably have some importance. The man intraocular pressure in a normal population varies between 15.1 mmHg and 16.5 mmHg (occasionallly 17.2 mmHg. The standard deviation varies from 2.5 mmHg to 3.8 mmHg...
.... Slight fluctuations in the normal intraocular pressure of about 1.5 mmHg are seen under the influence of the seasons, and larger variations occur between day and night. Shiose explained the lower intraocular pressure in the summer by the lower blood pressure in that season. Fluctuations in the intraocular pressure during the day may be associated with changes in the adrenocorticosteroid levels in the blood.
In normal subjects the intraocular pressure shows fluctuations in the daytime of 3-6 mmHg., whereas in glaucoma patients this variation can be more han 10 mmHg. Drance found a fluctuation in the daytime pressure of 5 mmHg or less in 84% of normal eyes and in only 6% of untreated glaucomatous eyes; 48% of the glaucomatous eyes showed pressure variations of 10 mmHg or more. The intraocular pressures were measured with a Schiotz tonometer....
... Frampton et al. were interested in the influence of sleep on the intraocular pressure. They performed two studies. In the first study, 13 young, normal subjects were allowed to go to sleep normally. In the second study 15 normal subjects were kept awake. The intraocular pressures were measured very frequently in a sitting position with a non-contact tonometer. When sleep was prevented the lowest intraocular pressure was measured at 3.00 am. Six subjects who stayed awake until 6:00 am were allowed to go to sleep until 8:00 am. In contrast with nine subjects who were lying in bed awake, the intraocular pressure of these subjects rose rapidly when they were woken. Their intraocular pressure was also significantly higher than before they went to sleep. When the subjects were allowed to sleep all night, the intraocular pressure rose by 37%-248%; as soon as they got up the intraocular pressure returned to normal within 13 minutes.
Brown et al. reported that the intraocular pressure ater 30 minutes sleep was on the average 3.45 mmHg higher than just before going to sleep. The intraocular pressure continued to rise but more slowly up to a main increase of 6.41 mmHg. On waking 404 seconds were needed, on the average, to return to the normal intraocular pressure. This same phenomenon has been described in glaucoma patients with known pressure peaks upon awakening: within 30 minutes the intraocular pressure decreased in half of the patients. ...
Niesel and Tarek calculated that, on statistical grounds, 12 measurements of introcular pressure, spaced out over a number of days and recorded as day-curves, are necessary to determine the highest level of intraocular pressure in patients undergoing treatment for open and closed angle glaucoma. Increasing the number of measurements from 12 to 20 hardly improved the chance of finding a pressure peak. Spacing the measurements and increasing their number is also the objective of the home tonometry described by Wilensky et al., which has the further advantage that measurements can be made outside normal office hours. Wilensky et al. found levels higher than 22 mmHg in more than half of his NPG patients; the patients had been instructed to measure the intraocular pressure five times a day for three to six days. High levels were mainly found when there was visual field progression or when progression was suspected.
In our study, no relationship was found between the level of the intraocular pressure and visual field progression. It has not as yet been possible to devise a practical method for the continuous registration of the intraocular pressure. This would obviously provde the most information about variations in intraocular pressure and maximum pressure levels.
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