A comparison of the circadian rhythm of intraocular pressure in primary chronic angle closure glaucoma, primary open angle glaucoma and normal eyes

Purpose: To evaluate the circadian rhythm of intraocular pressure (IOP) in primary chronic angle closure glaucoma (PCACG), primary open angle glaucoma (POAG), and normal eyes. Methods: Cross-sectional study of newly diagnosed patients of POAG (60 eyes), PCACG following laser iridotomy (75 eyes), and age and sex matched normal controls (75 eyes). All subjects underwent applanation tonometry at 7 a.m., 10 a.m., 1 p.m., 4 p.m., 7 p.m., and 10 p.m. by a masked observer. Circadian rhythms were classified based upon the timing and presence of peak pressure. Results: Age and gender in all three groups were comparable. Diurnal IOP fluctuations were significantly higher in PCACG (7.69±3.03 mmHg) and POAG (8.31±2.58 mmHg) groups compared to normal controls (4.83 ± 2.46 mmHg). PCACG eyes and controls had similarly timed circadian rhythms, with PCACG eyes having a consistently higher IOP. At 7 and 10 a.m., IOP peaked more often in POAG eyes compared to PCACG eyes. A plateau type of circadian rhythm was most common in normal eyes. The timing of peak IOP could be significantly correlated with the type of primary glaucoma examined. Conclusion: Afternoon peaks were more common in postiridotomy PCACG eyes, similar to the rhythm in normal eyes. Morning peaks were more frequent in POAG eyes. Diurnal fluctuation > 6 mmHg, associated with an IOP of 21 mmHg or more was never seen in a normal eye.