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Editors Selection IGR 16-4

Examination methods: IOP: 24-hrs Peak IOP registration

Comment by John Liu on:

17581 Relationships between 24h observations in intraocular pressure vs blood pressure, heart rate, nitric oxide and age in the Medical Chronobiology Aging Project, Perlman JI; Delany CM; Sothern RB et al., Clinica Terapeutica, 2007; 158: 31-47

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Perlman et al. (516) reviewed laboratory records of clinically healthy men, without any history of eye disease, enrolled in an ongoing research project on aging and biological rhythms.

Data of intraocular pressure (IOP), systolic and diastolic blood pressures, and heart rate were collected along with more than 100 other parameters every three hours during six 24-hour recording sessions over a period of 34 years. Supine IOPs were measured using the Schiotz tonometer for the three earlier sessions and the Tonopen for the latter sessions. Blood pressures and heart rate were measured in the sitting position. Sample sizes for the recording sessions were in the range of 10-13, and some subjects participated in all or most of the six recording sessions. The authors found that IOP, systolic and diastolic blood pressures, and heart rate showed circadian rhythms when evaluating all the data together. The majority of peak IOPs appeared during the late morning hours and the troughs appeared during the late evening hours or at night. Peak 24-hour blood pressures and heart rate appeared in the evening.

While the peak 24-hour systolic blood pressure appeared consistently during evening hours for all the ages, the appearance of peak 24-hour IOP changed significantly

The focus of the main ongoing project was not on IOP. Therefore, collections of IOP data were not comprehensive. It was unusual that measurements of IOP were not performed using the gold standard applanation tonometer in the sitting position, considering that blood pressures were measured sitting only for 24 hours. Despite many shortcomings, there were interesting observations. First, while the peak 24-hour systolic blood pressure appeared consistently during evening hours for all the ages, the appearance of peak 24-hour IOP changed significantly. When the subjects were in their 30s, the peak IOP often appeared in the morning hours before awakening. When the subjects were older, the peak 24-hour IOP shifted toward the hours after awakening. The authors also observed a moderate, positive correlation between time pairs of IOP and systolic blood pressure. A surprising finding was that the phase timings of cosine-fitted 24-hour IOP and systolic blood pressure were off by about 10 hours, or even more when the subjects were in their 30s.

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