Diurnal Intraocular Pressure and the Relationship With Swept-Source OCT–Derived Anterior Chamber Dimensions in Angle Closure: The IMPACT Study

Purpose: To evaluate diurnal intraocular pressure (DIOP) among individuals with Primary Angle Closure (PAC) or Primary Angle Closure Suspect (PACS). Additionally the hypothesis that greater DIOP fluctuation is related to smaller angle parameters was investigated. Methods: 40 Caucasian newly referred untreated patients with bilateral PAC or PACS were recruited. Intraocular pressure (IOP) was measured hourly between 09.00 and 16.00 with Goldmann applanation tonometry. DIOP fluctuation was defined as difference between maximum and minimum IOP. Angle Opening Distance, AOD; Trabecular-Iris Angle (TIA); Angle Recess Area (ARA); Trabecular Iris Space Area (TISA) were measured with AS-OCT (CASIA) in dark (0.3-0.5 lux) and light (170-200 lux) on the same day as DIOP measurements in eight angle sections. Results: IOP declined as the day progressed (p<0.001), unrelated to presence of PAS. At each timepoint, eyes with PAS (n=31) had significantly higher IOPs than eyes without PAS (n=49; p=0.043). DIOP fluctuation varied from 1.50 mmHg to 14.50 mmHg (mean 5.99 mmHg, SD 2.70 mmHg). DIOP fluctuation was unrelated to PAS. Multiple-predictor models investigating association of angle dimensions and greater DIOP fluctuation were statistically significant for AOD 750 (light), ARA 750 (light and dark), TISA 500 (light), TISA 750 (light), TIA 500 (light) and TIA 750 (light and dark). Conclusions: DIOP variation has clinical implications given that IOP level is used to distinguish between diagnostic categories of PACS and PAC. OCT angle parameter measurements may predict for magnitude of IOP diurnal fluctuations in at-risk patients, which may be clinical useful when considering a clinical intervention.