Objective: This study evaluates the differences in aqueous humor dynamics between daytime and nighttime in patients with ocular hypertension (OHT).
Methods: Thirty patients (58.9±11.0 years) with OHT were enrolled in the study. Subjects were studied at one daytime and one nighttime visit. Measurements include central cornea thickness (CCT) by pachymetry, intraocular pressure (IOP) by pneumatonometry, aqueous flow (Fa) by fluorophotometry, outflow facility by tonography (Cton), and seated systolic (SBP) and diastolic (DBP) blood pressure by sphygmomanometry at both visits. Daytime measurements only were made of episcleral venous pressure (Pev) by venomanometry, anterior chamber depth (ACd) by pachymetry, and outflow facility by fluorophotometry (Cfl). Nighttime IOP measurements were made both in the seated and supine positions. Uveoscleral outflow was calculated mathematically during the day and at night (Futon). One-way repeated measures ANOVA was used to compare daytime seated IOPs versus nighttime seated or supine IOPs. All other comparisons were made by two-tailed paired t-tests. P values< 0.05 were considered statistically significant.
Results: Compared with daytime seated IOP (21.3±3.5 mmHg), nighttime seated IOP (17.2±3.7 mmHg) was significantly reduced (p<0.001) and nighttime supine IOP (22.7±4.6 mmHg, habitual position) was increased (p=0.03). CCT was increased at night from 570±39 to 585±46 μm (p<0.001). There was a 47% nocturnal reduction in aqueous flow from 2.09±0.71 to 1.11±0.38 μL/min (p<0.001). Uveoscleral outflow was significantly reduced (p=0.02) by145% at night when using supine IOP and Pev adjusted for postural changes in the Goldmann equation. Tonographic outflow facility and all other measurements were unchanged.
Conclusion: The study shows that significant ocular changes occur at night in patients with ocular hypertension including thickening of CCT, decrease of Fa and Futon, reduction in seated IOP but increase in supine IOP. Compared to our previous study of ocular normotensive volunteers of similar age, OHT patients had decreased uveoscleral outflow but unchanged outflow facility at night.
Supported by an unrestricted grant from Pfizer; Research to Prevent Blindness