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Abstract #21014 Published in IGR 10-2
Circadian variation of aqueous dynamics in young healthy adults
Sit AJ; Nau CB; McLaren JW; Johnson DH; Hodge DInvestigative Ophthalmology and Visual Science 2008; 49: 1473-1479
See also comment(s) by John Liu •
PURPOSE: Recent research indicates that intraocular pressure (IOP) does not decrease significantly during the nocturnal period, although aqueous humor flow decreases by 50% or more at night. This study was undertaken to investigate whether changes in outflow facility, episcleral venous pressure, or uveoscleral flow at night could account for the nocturnal IOP. METHODS: Sixty-eight eyes of 34 healthy subjects (age, 18-44 years; mean, 29) were studied. Aqueous humor flow rate, IOP, and outflow facility were measured with pneumatonometry, anterior chamber fluorophotometry, and Schiotz tonography respectively, in each eye during the mid-diurnal (2-4 PM) and mid-nocturnal (2-4 AM) periods. Nocturnal IOP, flow rate, and outflow facility were compared to the same variables during the diurnal period. Mathematical models based on the modified Goldmann equation were used to assess the conditions under which these results could be reconciled. RESULTS: Supine IOP decreased slightly from 18.9 ± 2.7 mmHg in the mid-diurnal period to 17.8 ± 2.5 mmHg in the mid-nocturnal period (mean ± SD, P = 0.001). Aqueous flow rate decreased from 2.26 ± 0.73 to 1.12 ± 0.75 μL/min (mean ± SD, P < 0.001). There was a nonsignificant trend toward a nocturnal decrease of outflow facility (diurnal, 0.27 ± 0.11 μL/min/mmHg; nocturnal, 0.25 ± 0.08 μL/min/mmHg; mean ± SD, P = 0.13). CONCLUSIONS: Outflow facility measured by tonography does not decrease enough during the nocturnal period to compensate for the decreased aqueous humor flow rate. Modeling results indicate that the experimental results could be reconciled only if nocturnal changes in episcleral venous pressure and/or uveoscleral flow occurred.
Classification:
2.6.2 Outflow (Part of: 2 Anatomical structures in glaucoma > 2.6 Aqueous humor dynamics)
6.1.2 Fluctuation, circadian rhythms (Part of: 6 Clinical examination methods > 6.1 Intraocular pressure measurement; factors affecting IOP)
