Diurnal and seasonal variations in intraocular pressure in the rabbit

The diurnal variations in intraocular pressure in the rabbit were measured during a period of 12 months in a cross-sectional study. The average intraocular pressure of all the measurements taken during the year was 19·6 ± 2·0 mmHg (mean ± s.d.; n = 1957). The daily curve showed a continuous rise during the day from 18·2 ± 1·7 mmHg ( n = 175) at 0800 hr to 20·6 ± 1·8 mmHg ( n = 167) at 1700 hr. During the month of June, when the measurements were extended until midnight, this rise in intraocular pressure continued until 2200 hr, reached a level of 22·5 ± 1·6 ( n = 16), and started to decline. A similar daily pattern was observed throughout the year. The annual curve showed two peaks, during the summer and winter seasons, with a daily average of 20·2 ± 2·1 ( n = 404) and 20·2 ± 2·0 ( n = 638) respectively. The lowest average daily IOP value was obtained during the spring and was 18·8 ± 2·0 ( n = 509). An intermediate level between the summer/winter and the spring values was obtained during the autumn and was 19·4 ± 1·7 ( n = 406).