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M. D. Twa, D. C. Lozano; Evaluation of the Circadian Rhythm of IOP in the Brown Norway Rat. Invest. Ophthalmol. Vis. Sci. 2010;51(13):578.
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© ARVO (1962-2015); The Authors (2016-present)
Intraocular pressure varies over the 24 hour diurnal cycle and this variation may be an important factor in the neurodegeneration of glaucoma. The purpose of this study was to assess the diurnal variation in IOP in the Brown Norway rat, a species commonly used as an animal model of chronic open angle glaucoma.
The right eyes of 10 8-month old male animals (300-450 g) were measured repeatedly using a calibrated rebound tonometer every two hours over a 26 hour period. The animals were initially housed in a 12 h light/12 h dark cycle (L/D). Later, the animals were switched to a dim constant illumination (L/L; 60 lux) and after 30 days, IOP was measured as before. The variation in IOP over the diurnal cycle was compared as a function of the illumination conditions.
Under the L/D paradigm, the IOP during the light period was 15.1 ± 4.3 mm Hg (mean ± SD) ; IOP during the dark period was 27.3 ± 3.5 mm Hg. After 30 days exposure to the constant illumination paradigm the animals continued to show a circadian rhythm of IOP with elongation of the period of lower IOP (from 12 to 18 h); and a phase shift (14 h) of the peak IOP. The average IOP during the peak period was 27.3 ± 3.3 mm Hg; the average for the remaining period was 16.2 ±4.4 mm Hg. When averaged over the previously defined light/dark time periods, the diurnal variation in IOP appears muted and phase inverted.
After 30 days of a constant dim illumination paradigm, circadian rhythms of IOP were altered, but present in the aged male Brown Norway rat. These results suggest that diurnal variation in IOP may still play a role in the induction of experimental glaucoma under free-running circadian rhythm conditions.
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