The dynamic balance between aqueous production and outflow leads to IOP fluctuation in healthy and glaucomatous eyes. The pattern of IOP fluctuation can be highly variable and sensitive to the effects of body posture, hydration, and aging. Maximal IOP in this study was measured in the morning (9–11:30 AM) for the majority of participants. Wilensky
2 observed that 65% of normal subjects (defined as subjects with normal IOPs, normal visual acuity, healthy optic nerve heads, and no history of ocular disease) had DIOP peaks between 8 AM and 2 PM while 30% exhibited a peak IOP between 4 and 8 AM. Differing results were reported for those diagnosed as ocular hypertensive (IOP > 22 mm Hg and no signs of glaucoma), with 51% presenting their peaks between 4 and 8 AM and 42% between 8 AM and 2 PM. In the case of the present study, if an IOP-based criterion equivalent to that in the study by Wilensky
2 is used (22 mm Hg or less) and the presence of PAS is ignored, 28 of 40 participants (70%) had IOP ≤ 22 mm Hg in both eyes during the diurnal period. Of these 28 participants, 27 (96%) exhibited an IOP peak between 9 AM and 2 PM. Of the participants with IOP > 22 mm Hg in at least one eye (
n = 12), all had a peak IOP that occurred between 9 and 11 AM. To summarize, in both this study and that of Wilensky,
2 diurnal peaks are more frequently found in the morning than in the late afternoon (after 2 PM), and this was unrelated to a particular IOP cutoff.
The DIOP pattern found for this group of subjects is similar to that in a study of 21 healthy individuals in a similar age group and of mixed ethnicity (15 of 21 subjects were Caucasian) by Liu et al.
3 In that study, Liu et al.
3 reported a peak in the early morning of approximately 18 mm Hg and a decrease throughout the morning to levels of 17 mm Hg with a moderate increase in the middle of the day (12 PM) of approximately 0.5 mm Hg, decreasing further to levels of 17 mm Hg in the early evening (4 PM). It is therefore an interesting observation that, despite the fact that the participants in the present study had narrow angles and higher DIOP fluctuation, the DIOP behavior was similar to that reported for patients with open angles in other studies.
Of 80 eyes of 40 patients examined at visit 1, 49 were diagnosed as PAC and 31 as PACS. From those eyes diagnosed as PAC, 17 were due to presence of PAS only; 18 were due to a raised IOP only (IOP higher than or equal to 21 mm Hg at any time between 9 AM and 4 PM); and 14 were due to a combination of PAS and IOP criteria. Of the 18 eyes diagnosed with PAC due to IOP levels only, 15 would have been diagnosed as PACS had the IOP measurements been taken in the afternoon (12:30–4 PM). This highlights the observation that the timing of a single IOP measurement by a clinician is of importance when considering which diagnosis to ascribe to a patient with angle closure. In this case, six participants might be ascribed the lower-risk PACS diagnosis had the single afternoon IOP measurement been the only measure used to reach a diagnosis. This may be of clinical importance given that the management and follow-up of patients diagnosed as PAC differ from those for individuals diagnosed as PACS.
To date there are no published studies that report the relationship of DIOP with PAS. The present study found a statistically significant effect of the presence of PAS on DIOP. The IOP of an eye with PAS was on average 1.5 mm Hg higher than in an eye without PAS. Furthermore, the increase in IOP was found to be directly related to the degree of PAS present in an eye at the majority of the diurnal time points.
Few studies have reported diurnal fluctuation of IOP for normal (nonglaucomatous) and glaucomatous eyes.
9,13,14 A literature search failed to identify studies investigating DIOP fluctuation among untreated individuals with angle closure in the absence of glaucoma. In a study of Chinese patients whose eyes had previously been treated with laser peripheral iridotomy with a diagnosis of PAC or primary angle closure glaucoma, Baskaran et al.
9 reported higher levels of fluctuations in these patients (fluctuation defined as the difference between peaks and troughs of DIOP).
9 In that study, PAC and PACG patients presented with greater diurnal fluctuation of 5.4 ± 2.4 and 4.5 ± 2.3 mm Hg, respectively (IOP measured every hour from 8:30 AM to 4:30 PM), compared to those with PACS and normal subjects with open angles, 3.7 ± 1.2 and 3.8 ± 1.1 mm Hg, respectively. The same study reported a relationship between the diurnal fluctuation of IOP in the same eye and the degree of PAS of these patients. These findings differ from those in our study, in which fluctuation of DIOP was not related to age, sex, or PAS. In the case of the present study, the lack of a relationship is not unexpected given that the DIOP patterns of those eyes with presence of PAS and those eyes without were very similar (
Fig. 5). Although there may have been differences between the peaks and troughs between patterns, the fluctuation obtained would have been similar. In the study by Baskaran et al.,
9 the data showed a high degree of variation and, although the relationship was reported as statistically significant (
P = 0.013), the relationship was weak (
R2, 0.139).