April 2015
Volume 56, Issue 4
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Glaucoma  |   April 2015
Evaluation of Choroidal Thickness, Intraocular Pressure, and Serum Osmolality After the Water Drinking Test in Eyes With Primary Angle Closure
Author Affiliations & Notes
  • Monisha E. Nongpiur
    Singapore Eye Research Institute, Singapore
    Duke-NUS Graduate Medical School, Singapore
    Yong Loo Lin School of Medicine, National University of Singapore, Singapore
  • Valencia H. X. Foo
    Yong Loo Lin School of Medicine, National University of Singapore, Singapore
  • John Mark de Leon
    Singapore Eye Research Institute, Singapore
  • Mani Baskaran
    Singapore Eye Research Institute, Singapore
    Duke-NUS Graduate Medical School, Singapore
    Yong Loo Lin School of Medicine, National University of Singapore, Singapore
  • Tin A. Tun
    Singapore Eye Research Institute, Singapore
  • Rahat Husain
    Singapore National Eye Centre, Singapore
  • Shamira A. Perera
    Singapore National Eye Centre, Singapore
  • Tin Aung
    Singapore Eye Research Institute, Singapore
    Yong Loo Lin School of Medicine, National University of Singapore, Singapore
    Singapore National Eye Centre, Singapore
  • Correspondence: Tin Aung, Singapore National Eye Centre, 11 Third Hospital Avenue, Singapore 168751; aung.tin@snec.com.sg
Investigative Ophthalmology & Visual Science April 2015, Vol.56, 2135-2143. doi:10.1167/iovs.14-15280
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      Monisha E. Nongpiur, Valencia H. X. Foo, John Mark de Leon, Mani Baskaran, Tin A. Tun, Rahat Husain, Shamira A. Perera, Tin Aung; Evaluation of Choroidal Thickness, Intraocular Pressure, and Serum Osmolality After the Water Drinking Test in Eyes With Primary Angle Closure. Invest. Ophthalmol. Vis. Sci. 2015;56(4):2135-2143. doi: 10.1167/iovs.14-15280.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose.: We evaluated changes in choroidal thickness (ChT), IOP, ocular biometry, and serum osmolality after the water drinking test (WDT) in subjects with previous acute primary angle closure (APAC) and primary angle closure glaucoma (PACG).

Methods.: We evaluated 38 subjects, including 21 with APAC and 17 with PACG. Each subject underwent IOP measurement, A-scan biometry, spectral domain-optical coherence tomography (SDOCT), anterior segment-optical coherence tomography (ASOCT), and osmolality measurements at baseline, 30, and 60 minutes after consuming at least 10 mL/kg of water. The ChT at the macula was measured from SDOCT images using the 7-line scan protocol. The fellow-eyes of APAC (FE-APAC) were compared to eyes with PACG.

Results.: The mean age ± SD of the study subjects was 62.8 ± 8.6 years and 21 (55.3%) were females. At baseline, serum osmolality was significantly lower (P < 0.001) in the FE-APAC group, whereas ChT was similar in both groups (P = 0.56). At 30 minutes after WDT, both groups demonstrated a significant increase in IOP (FE-APAC, 3.0 [95% confidence interval {CI}, 1.52, 4.48] mm Hg; PACG, 5.06 [95% CI, 3.68, 6.26] mm Hg; P < 0.001 for both) and decrease in serum osmolality (P < 0.001 for both), but no significant change in ChT. The magnitude of change in IOP was significantly greater in PACG eyes (P = 0.04). After multivariate analysis, a lower mean baseline serum osmolality (β = −0.44, P = 0.003) was associated with a greater change in ChT at 30 minutes after WDT.

Conclusions.: The increase in IOP after WDT was higher in PACG eyes compared to FE-APAC; however, the latter had lower serum osmolality at baseline. Change in mean ChT following WDT was associated with a lower baseline serum osmolality.

Acute primary angle closure (APAC) is an ophthalmic emergency that can lead to poor long-term visual outcomes, such as glaucomatous optic nerve damage and blindness in the affected eye.1,2 The fellow eyes of patients presenting with APAC are at high risk of APAC because both eyes share similar anatomical features.3 Certain drugs, environmental factors, and systemic conditions are known to precipitate APAC,4 but the underlying mechanisms are only partially understood, and it is not known if there is a final common pathway involved in its pathogenesis. 
The water drinking test (WDT) is a provocative test that indirectly evaluates the outflow system of the eye.5,6 An increase in IOP of 8 mm Hg after WDT is considered as indicative of risk for primary open angle glaucoma (POAG). Although, the test was used widely previously to diagnose POAG, it was later found to be wanting due to lack of standardization, and many false-positive and false-negative results.7,8 Recently, the WDT has attracted renewed attention when it was found to be an accessible marker of osmotically induced changes in choroidal thickness (ChT).9,10 Used as a stress test, it yields a good estimate of the peak diurnal IOP.5 Arora et al.10 studied changes in ChT after WDT across angle-closure and open-angle subjects. While a significant increase in ChT was noted in angle-closure eyes, the increases in IOP after the WDT were not fully explained by ChT increase alone, suggesting that there are other underlying mechanisms behind the IOP rise.10 
Clinical studies have suggested that choroidal expansion is a possible mechanism in APAC, being found in a proportion of such patients.11 Furthermore, within the angle closure disease spectrum, the subfoveal choroid has been shown to be thicker in APAC eyes compared to primary angle closure suspects (PACS) in cross-sectional studies.12,13 The thicker subfoveal choroid may be a surrogate for choroidal expansion that occurs in some individuals with APAC. 
Therefore, in this study, by comparing fellow eyes of APAC (FE-APAC) and primary angle closure glaucoma (PACG) eyes, we aimed to evaluate the association of changes in IOP, ChT, serum osmolality, and anterior segment structures after the WDT. We hypothesized that associations between the above factors may partly explain the predisposition for an APAC attack. 
Methods
Subjects
This prospective study was approved by the Institutional Review Board of the hospital and adhered to the provisions of the Declaration of Helsinki for research involving human subjects. Written informed consent was obtained from all participants involved in the study. One eye of each subject was included. 
The two subgroups of angle closure subjects recruited into the study were FE-APAC and chronic PACG. The APAC was defined according to the following criteria.14 Presence of at least two of the following symptoms: ocular or periocular pain, nausea and/or vomiting, and an antecedent history of intermittent blurring of vision with halos; presenting IOP of at least 22 mm Hg (as measured by Goldmann applanation tonometry), and the presence of at least three of the following signs: conjunctival injection, corneal epithelial edema, mid-dilated unreactive pupil, and a shallow anterior chamber in addition to the presence of occludable angles defined as the inability to visualize the posterior trabecular meshwork for at least 180° on nonindentation gonioscopy.14 We diagnosed PACG on the basis of occludable angles with glaucomatous optic neuropathy (defined as vertical cup-to-disc [CDR] ratio of >0.7, CDR asymmetry >0.2, and/or focal notching) with compatible visual field loss on static automated perimetry (SITA Standard algorithm with a 24-2 test pattern; Humphrey Visual Field Analyser II; Carl Zeis Meditec, Dublin, CA, USA). This was defined as Glaucoma Hemifield Test outside normal limits; a cluster or 3 or more, nonedge, contiguous points on the pattern deviation plot, not crossing the horizontal meridian with a probability of <5% being present in age-matched normals (one of which was <1%); and an abnormal pattern standard deviation (PSD) with P < 5% occurring in the normal population, and fulfilling the test reliability criteria (fixation losses <20%, false-positives <33% and/or false-negatives <33%). All FE-APAC eyes had IOP ≤ 21 mm Hg and appositional angle closure on gonioscopy and no evidence of peripheral anterior synechiae (PAS) or glaucomatous optic neuropathy. 
As an additional analysis, we also compared the angle closure eyes, including FE-APAC and PACG versus normal eyes. Normal subjects were defined as having an IOP < 21 mm Hg, open angles on gonioscopy, healthy optic nerves, and no family history of glaucoma. All study eyes had not had any intraocular surgery or trauma. 
All subjects with angle closure had undergone laser peripheral iridotomy (LPI). The interval between LPI and the study recruitment is 37.2 ± 27.8 months (range, 7–123 months; median, 30 months). Subjects with secondary causes of angle closure, such as a phacomorphic component/subluxed lens, angle closure patients who had laser peripheral iridoplasty, corneal disorders that preclude adequate imaging of the angles, such as extensive pterygium and peripheral corneal opacity, were excluded. Subjects with a pre-existing cardiac disease, including congestive cardiac failure also were excluded. 
Examination
Study subjects underwent a standardized ophthalmic evaluation, including slit-lamp biomicroscopy, IOP measurement (applanation tonometry), gonioscopy, A-scan biometry (US-800; Nidek Co. Ltd., Tokyo, Japan), spectral domain-optical coherence tomography (SDOCT, Spectralis; Heidelberg Engineering, Heidelberg, Germany), anterior segment-optical coherence tomography (ASOCT, Visante; Carl Zeiss Meditec), and venous blood serum osmolality measurements at baseline, 30, and 60 minutes after consumption of at least 10 mL/kg of water within 5 minutes.15 Serum osmolality could not be analyzed for three subjects at baseline, and five subjects each at 30 and 60 minutes either due to poor vein access, insufficient or hemolysed specimens. Axial length (AL), anterior chamber depth (ACD), and lens thickness (LT) measurements were obtained from the A-scan biometry. Both SD-OCT and AS-OCT imaging were performed by a single masked operator. 
Anterior Segment Imaging and Analysis
All subjects underwent imaging with ASOCT (Visante; Carl Zeiss Meditec) performed under standardized dark room conditions (0 lux). One cross-sectional horizontal ASOCT scan of the nasal and temporal angle was evaluated for each subject. The images were processed using customized software, the Zhongshan Angle Assessment Program (ZAAP, Guangzhou, China).16 The parameters measured by the software include angle opening distance at 750 μm from scleral spur (AOD750); trabecular-iris space area (TISA750)17; anterior chamber width, area, and volume (ACW, ACA, ACV)18,19; lens vault20; iris thickness; and iris cross-sectional area.21 
Imaging and Measurement of ChT
The choroid images were obtained by using SD-OCT (Spectralis; Heidelberg Engineering). The macular region around the fovea of the study eye was scanned using a 7-line scan protocol (scan width 30° and 25 averaging) with enhanced depth imaging (EDI). One scan at each time point was taken for each subject; however, if the image had poor visualization of the choroidal–scleral interface (CSI), the border between the choroid and sclera, an additional scan was taken. The optical magnification was estimated by entering the keratometry and refractive readings to the SD-OCT software before scanning. A single masked grader (VF) manually selected the image centered on the fovea from seven images and manually measured the ChT by using the line caliber tool, native to Heidelberg Eye Explorer software (version 5.6.1.0). The ChT was defined as the perpendicular distance from the external portion of the RPE, Bruch's membrane, to the CSI. The ChT of the fovea was measured at the thinnest/central point of the fovea. Measurements also were taken at six additional points at 0.5, 1.0, and 1.5 mm nasal and temporal to the fovea, respectively (Fig. 1). The mean ChT was calculated as the average of the seven measurements. The images from 7, 9, and 12 subjects at baseline, 30, and 60 minutes, respectively, were excluded as the CSI was not clearly visible. 
Figure 1
 
SDOCT (enhanced depth imaging) image showing measurement of macular ChT at the subfovea, and 0.5, 1, and 1.5 mm nasal and temporal to the fovea, respectively.
Figure 1
 
SDOCT (enhanced depth imaging) image showing measurement of macular ChT at the subfovea, and 0.5, 1, and 1.5 mm nasal and temporal to the fovea, respectively.
Statistical Analysis
Statistical analysis was performed using the statistical package IBM SPSS Statistics for Windows (Version 21.0; IBM Corp., Armonk, NY, USA). The time points for the study were baseline, 30, and 60 minutes after the WDT. Paired t-test for parametric data and Wilcoxon signed-rank test for nonparametric data were used to assess the mean changes in the continuous variables from baseline at each individual time point. An appropriate Bonferroni correction (α/3) was applied to correct for the number of time-point evaluated resulting in a P value threshold of 0.017 to be considered statistically significant. The between-group differences (FE-APAC versus PACG, PACG versus normals, and FE-APAC versus normals) were evaluated by independent t-test and Mann-Whitney U test for parametric and nonparametric data, respectively. Univariate linear regression analysis adjusted for age and sex were performed for baseline parameters with change in mean ChT at 30 minutes (calculated as mean ChT at 30 minutes-baseline mean ChT) as the dependent variable. This was followed by a multivariate linear regression analysis using baseline parameters that showed significance at 0.20 levels in univariate analysis, excluding those that showed multicollinearity. Variance inflation factor and tolerance were calculated to test potential multicollinearity among the independent variables. The R2 was evaluated to examine the adequacy of the multiple linear regression models. A general linear model (GLM) for repeated measures analysis of ChT at the three time-points also was performed adjusting for covariates age, sex, baseline IOP, baseline osmolality and comparing between FE-APAC and PACG. By assuming a mean difference in ChT of 0.2 mm and a SD of 0.19 mm after WDT,9 with power of 90% and α of 5%, the sample size for a 2-sided test was 20 subjects each for cases and controls. 
Results
Demographic and Baseline Characteristics of Subjects
We recruited 21 FE-APAC and 17 PACG eyes, with only one eye per subject included. The mean age (SD) of the subjects was 61.4 (9.2) years and there were 32 (55.2%) females. Baseline characteristics of the subjects are summarized in Table 1. Compared to PACG, the FE-APAC subjects had significantly smaller CDR (P < 0.001). There were no significant differences in age, ACD, AL, LT, and other ASOCT parameters. Serum osmolality was significantly lower in the FE-APAC subjects compared to PACG (P < 0.001) at baseline. Baseline ChT was not significantly different between the two groups (P = 0.56). 
Table 1
 
Baseline Characteristics of Study Subjects
Table 1
 
Baseline Characteristics of Study Subjects
A total of 20 normal eyes from 20 subjects each also was recruited. In the comparison of baseline characteristics between eyes with FE-APAC, PACG, and normal (Table 1), eyes with either FE-APAC or PACG had significantly smaller ACA and ACV, narrower anterior chamber angles, and larger lens vault (LV, P < 0.006 for all). The lens was thicker in FE-APAC compared to normals (P = 0.01). The FE-APAC subjects also were noted to have significantly lower serum osmolality at baseline compared to normal (P = 0.004). Overall, majority of our subjects were of Chinese ethnicity (N = 49, 84.5%). 
Post-WDT Comparison Between FE-APAC and PACG Eyes
At 30 minutes after the WDT, as summarized in Table 2, there was a significant increase in IOP and decrease in serum osmolality in both groups (pairwise P < 0.017 for all), while a significant increase in IOP at 60 minutes was noted only in the PACG group (P < 0.006). The PACG eyes experienced a significantly higher increase in IOP (FE-APAC 3.0 [95% confidence interval {CI}, 1.52, 4.48 mm Hg versus PACG 5.06 [95% CI, 3.68, 6.26 mm Hg; P = 0.02]) and greater decrease in serum osmolality compared to FE-APAC subjects (P = 0.02). 
Table 2
 
Comparison of Changes in Parameters of Angle Closure Subjects at 30 and 60 Minutes After the WDT
Table 2
 
Comparison of Changes in Parameters of Angle Closure Subjects at 30 and 60 Minutes After the WDT
An increase in mean ChT was noted in FE-APAC compared to PACG eyes at 30 minutes (4.3 [95% CI, −5.35, 13.97] μm versus −9.1 [95% CI, −19.5, 1.3] μm), but the difference was not statistically significant (P = 0.06). No significant differences in the changes in biometric and ASOCT parameters were noted either within (pairwise P > 0.017 for all) or between (P > 0.05) the two groups at 30 and 60 minutes. The GLM with repeated measures analysis comparing FE-APAC and PACG for change in ChT, showed borderline significance of P = 0.052 for baseline osmolality at an observed power of 58%. 
Post-WDT Comparison Between Angle Closure Groups and Normal Eyes
At 30 minutes after the WDT, as summarized in Table 3, there was a significant increase in IOP and decrease in serum osmolality within all the groups (pairwise P < 0.017 for all), while a significant increase in IOP at 60 minutes was noted only in the PACG group (P < 0.006). Compared to normal eyes, only the PACG eyes experienced a significantly higher increase in IOP (P = 0.01) and a greater decrease in serum osmolality compared to normal eyes (P = 0.01). No significant differences in ChT were noted either within (pairwise P > 0.017 for all) or between (P > 0.05) the groups at 30 and 60 minutes. 
Table 3
 
Comparison of Changes in Parameters Between Angle Closure Subtypes and Normals at 30 and 60 Minutes After the WDT
Table 3
 
Comparison of Changes in Parameters Between Angle Closure Subtypes and Normals at 30 and 60 Minutes After the WDT
Comparison of changes in biometric and ASOCT parameters also showed no significant differences either within (pairwise P > 0.017 for all) or between (P > 0.05) the groups at 30 and 60 minutes (data not shown). 
Figures 2 to 4 illustrate the inter-relation among IOP, osmolality, and ChT changes following the WDT. In the three groups, there was an initial rise in IOP and a concomitant drop in serum osmolality. In FE-APAC, the ChT increased from baseline to 30 minutes after the WDT, while in PACG eyes, the ChT initially decreased at 30 minutes followed by an increase at 60 minutes after WDT. In the normals, the ChT remained largely unchanged. 
Figure 2
 
Illustration of the change in IOP, osmolality, and ChT at 30 and 60 minutes following the WDT in FE-APAC subjects.
Figure 2
 
Illustration of the change in IOP, osmolality, and ChT at 30 and 60 minutes following the WDT in FE-APAC subjects.
Figure 3
 
Illustration of the change in IOP, osmolality, and ChT at 30 and 60 minutes following the WDT in PACG subjects.
Figure 3
 
Illustration of the change in IOP, osmolality, and ChT at 30 and 60 minutes following the WDT in PACG subjects.
Figure 4
 
Illustration of the change in IOP, osmolality, and ChT at 30 and 60 minutes following the WDT in normal subjects.
Figure 4
 
Illustration of the change in IOP, osmolality, and ChT at 30 and 60 minutes following the WDT in normal subjects.
Age- and sex-adjusted univariate linear regression analysis performed for baseline predictors of change in ChT at 30 minutes showed a significant association with lower serum osmolality and a thinner lens. The multivariate linear regression model found significant associations with lower baseline serum osmolality (P = 0.005, R2 = 0.26, Table 4). No significant predictors were associated with change in IOP at 30 minutes after WDT. 
Table 4
 
Factors Associated With Change of Mean ChT From Baseline to 30 Minutes After the WDT
Table 4
 
Factors Associated With Change of Mean ChT From Baseline to 30 Minutes After the WDT
At 60 minutes, the IOP of 4 subjects were noted to be >21 mm Hg; two with IOP of 22 mm Hg, one with 23 mm Hg, and another 24 mm Hg. The IOP were rechecked after half an hour and were noted to have spontaneously reduced to <21 mm Hg for all four subjects without any intervention. The intraobserver reproducibility of ChT measurements assessed in a random subset of 10 eyes was excellent at 0.92 (95% CI, 0.62–0.98) for mean ChT and 0.93 (95% CI, 0.71–0.98) for subfoveal ChT. 
Discussion
In this study, we investigated the concurrent effects of the WDT on serum osmolality, ChT, anterior segment biometry, and IOP in FE-APAC and PACG eyes. The FE-APAC group had a significantly lower baseline serum osmolality compared to the PACG group. At 30-minutes after WDT, both groups showed significant IOP increases and serum osmolality decreases, but no significant changes in ChT, even though a trend was noted in FE-APAC eyes. At 60 minutes, only PACG eyes had sustained IOP elevations. Notably, the serum osmolality levels even after the WDT-induced reduction were within the normal reference range for all subjects. 
While the FE-APAC group had a lower baseline osmolality, the PACG group experienced a greater drop in serum osmolality after WDT. Osmotic gradient may be a possible factor influencing IOP changes in some patients as the gradient leads to water movement into the aqueous humour with subsequent increase in IOP.22 It is not known whether the lower baseline osmolality in FE-APAC eyes predisposes them to a greater risk of APAC; such an association may be difficult to establish in the current study. Of note, all FE-APAC and PACG eyes had previously undergone a prophylactic laser iridotomy before the WDT which may alter the fluid dynamics. A lower baseline serum osmolality was significantly associated with a corresponding change in mean ChT at 30 minutes after WDT. The rapid water ingestion would lead to a transient increase in hydrostatic pressure and decrease in osmotic pressure, which shifts fluid from the systemic circulation to the choroidal space due to the osmotic gradient.22 The change in choroidal volume would be transmitted to the intraocular compartments causing fluid exit via the outflow facility by trabecular and uveoscleral pathways.11 Eyes may show a higher or lower IOP elevation depending on its outflow facility, as suggested by Brubaker.23 Interestingly, our findings of the lack of significant association between IOP rise and change in ChT were similar to the findings reported by Arora et al.10 and Mansouri et al.24 In the study by Arora et al.10 on the changes in ChT after WDT across angle-closure and open-angle subjects, it was proposed that the lack of significant changes in ChT during the WDT across all groups may have resulted from the concomitant increase in blood pressure (BP) and IOP, which, therefore, resulted in the perfusion pressure to remain unchanged.10 While our study did not evaluate the changes in BP, we presumed a similar effect of the WDT on BP in our subjects. Mansouri et al.24 speculated that choroidal expansion is an unlikely primary mechanism responsible for the IOP elevations induced by the WDT. Another possibility for the lack of association between IOP rise and ChT in our study could be due to the small sample size. 
The association between serum osmolality reduction and IOP elevations has been investigated by numerous studies during and after hemodialysis in end-stage renal failure patients, only to give mixed results.25–29 There seems to be a tendency for IOP to increase during hemodialysis in patients with narrow angles due to abnormal aqueous outflow.26 These studies suggest that serum osmotic gradient is possibly the driving mechanism for IOP alterations in conventional hemodialysis, and support the theory of a significant inverse correlation between serum osmolality and IOP rise. The removal of solutes during hemodialysis leads to a decrease in plasma osmolality in the cellular compartment, followed by an influx of fluid into the ciliary body, which induces an increase in the production of aqueous humor, thereby resulting in elevated IOP.30 Furthermore, the rate of the serum osmolality decrease also could have an effect on IOP rise. In an animal study (on mongrel dogs), Sitprija et al.25 showed that a rate of decline of 11 mOsm/kg H2O/h in plasma osmolality was associated with a significant increase in IOP; however, with a slower rate of decline in plasma osmolality (8.5 mOsm/kg H2O/h), the rise increase in IOP was minimal. This may explain the absence of significant effect of WDT on ChT in our study and the differences seen in ChT between normal and angle closure eyes in the study by Arora et al.11 Whether lowered serum osmolality or its rate of alterations in susceptible eyes predisposes them to an acute attack is difficult to ascertain. Further exploratory studies are necessary to demonstrate such an association. 
The higher IOP elevations in PACG eyes compared to the FE-APAC after the WDT could be attributed to a greater impairment of aqueous outflow in PACG eyes; since FE-APAC eyes were characterized by the absence of signs of trabecular damage, such as PAS and/or elevated IOP, iris whorling, “glaucomfleken” lens opacities, or excessive pigment deposition on the trabecular surface.31 The outflow facility in the FE-APAC eyes is more capable of adapting to aqueous output alterations. Furthermore, chronic trabecular damage also could explain the significant sustained increase in IOP at 60 minutes in the PACG group. 
While rapid choroidal expansion may contribute to the process of angle closure through forward anterior lens movement causing pupillary block,11 IOP increase does not solely arise from the increase in ChT.10,24 From our study, it may be postulated that the net IOP elevation could perhaps be a result of serum osmolality changes induced by the WDT coupled with trabecular damage in glaucomatous eyes leading to impaired aqueous outflow, which also may affect the choroid to some extent. Larger magnitude of alterations in the dynamic relationships between a lowered baseline osmolality, BP, greater osmotic gradient, choroidal expansion, and structurally-predisposed eyes may explain why some eyes develop an acute attack and others not. 
To our knowledge, our study is the first to examine differences in responses to the WDT between FE-APAC and PACG eyes in terms of serum osmolality, IOP, and mean ChT changes which occur independently of angle width alterations. We chose to evaluate FE-APAC as it is the nearest surrogate to an eye with APAC.3 However, we would like to emphasize that the experimental conditions in this study might not entirely simulate the rapid changes that likely occur during an acute episode including that of the angle alterations. Limitations of our study include the relatively small sample size which needs validation in a larger cohort. Additionally, the manual method for estimation of ChT and the limited area of assessment may not be firstly, reflective of, and secondly, capable of accurately quantifying the magnitude of the osmotic changes. We also did not evaluate for changes in circumpapillary ChT. Availability of automated image analysis software with an ability to estimate choroidal volume may result in a more accurate estimation of the changes that occur in the choroid. Ideally, long-term prospective studies evaluating changes in the dynamic relationships between systemic and ocular parameters in angle closure eyes may help identify inciting events for an acute attack, but such studies will be difficult to execute. 
In conclusion, we found that the increase in IOP after WDT was higher in PACG eyes compared to FE-APAC; however, the latter had lower serum osmolality at baseline. Change in mean ChT following WDT was associated with a lower baseline serum osmolality. 
Acknowledgments
Supported by a grant from the Singhealth Foundation, Singapore. The authors alone are responsible for the content and writing of the paper. 
Disclosure: M.E. Nongpiur, None; V.H.X. Foo, None; J.M. de Leon, None; M. Baskaran, None; T.A. Tun, None; R. Husain, None; S.A. Perera, None; T. Aung, None 
References
Sawada A, Aoyama A, Yamamoto T, Takatsuka N. Long-term therapeutic outcome of acute primary angle closure in Japanese. Jpn J Ophthalmol. 2007; 51: 353–359.
Aung T, Friedman DS, Chew PT et al. Long-term outcomes in Asians after acute primary angle closure. Ophthalmology. 2004; 111: 1464–1469.
Edwards RS. Behaviour of the fellow eye in acute angle-closure glaucoma. Br J Ophthalmol. 1982; 66: 576–579.
Subak-Sharpe I, Low S, Nolan W, Foster PJ. Pharmacological and environmental factors in primary angle-closure glaucoma. Br Med Bull. 2010; 93: 125–143.
Miller D. The relationship between diurnal tension variation and the water-drinking test. Am J Ophthalmol. 1964; 58: 243–246.
Spaeth GL. The water drinking test. Indications that factors other than osmotic considerations are involved. Arch Ophthalmol. 1967; 77: 50–58.
Roth JA. Inadequate diagnostic value of the water-drinking test. Br J Ophthalmol. 1974; 58: 55–61.
Rasmussen KE, Jorgensen HA. Diagnostic value of the water-drinking test in early detection of simple glaucoma. Acta Ophthalmol. 1976; 54: 160–166.
De Moraes CG, Reis AS, Cavalcante AF, Sano ME Susanna RJr. Choroidal expansion during the water drinking test. Graefe's Arch Clin Exp Ophthalmol. 2009; 247: 385–389.
Arora KS, Jefferys JL, Maul EA, Quigley HA. Choroidal thickness change after water drinking is greater in angle closure than in open angle eyes. Invest Ophthalmol Vis Sci. 2012; 53: 6393–6402.
Quigley HA, Friedman DS, Congdon NG. Possible mechanisms of primary angle-closure and malignant glaucoma. J Glaucoma. 2003; 12: 167–180.
Zhou M, Wang W, Ding X et al. Choroidal thickness in fellow eyes of patients with acute primary angle-closure measured by enhanced depth imaging spectral-domain optical coherence tomography. Invest Ophthalmol Vis Sci. 2013; 54: 1971–1978.
Huang W, Wang W, Gao X et al. Choroidal thickness in the subtypes of angle closure: an EDI-OCT study. Invest Ophthalmol Vis Sci. 2013; 54: 7849–7853.
Lee KY, Rensch F, Aung T et al. Peripapillary atrophy after acute primary angle closure. Br J Ophthalmol. 2007; 91: 1059–1061.
Goldberg I, Clement CI. The water drinking test. Am J Ophthalmol. 2010; 150: 447–449.
Console JW, Sakata LM, Aung T, Friedman DS, He M. Quantitative analysis of anterior segment optical coherence tomography images: the Zhongshan Angle Assessment Program. Br J Ophthalmol. 2008; 92: 1612–1616.
Narayanaswamy A, Sakata LM, He MG et al. Diagnostic performance of anterior chamber angle measurements for detecting eyes with narrow angles: an anterior segment OCT study. Arch Ophthalmol. 2010; 128: 1321–1327.
Nongpiur ME, Sakata LM, Friedman DS et al. Novel association of smaller anterior chamber width with angle closure in Singaporeans. Ophthalmology. 2010; 117: 1967–1973.
Wu RY, Nongpiur ME, He MG et al. Association of narrow angles with anterior chamber area and volume measured with anterior-segment optical coherence tomography. Arch Ophthalmol. 2011; 129: 569–574.
Nongpiur ME, He M, Amerasinghe N et al. Lens vault, thickness, and position in Chinese subjects with angle closure. Ophthalmology. 2011; 118: 474–479.
Wang B, Sakata LM, Friedman DS et al. Quantitative iris parameters and association with narrow angles. Ophthalmology. 2010; 117: 11–17.
Tovbin D, Belfair N, Shapira S et al. High postdialysis urea rebound can predict intradialytic increase in intraocular pressure in dialysis patients with lowered intradialytic hemoconcentration. Nephron. 2002; 90: 181–187.
Brubaker RF. Targeting outflow facility in glaucoma management. Surv Ophthalmol. 2003; 48 (suppl 1): S17–S20.
Mansouri K, Medeiros FA, Marchase N, Tatham AJ, Auerbach D, Weinreb RN. Assessment of choroidal thickness and volume during the water drinking test by swept-source optical coherence tomography. Ophthalmology. 2013; 120: 2508–2516.
Sitprija V, Holmes JH, Ellis PP. Changes in intraocular pressure during hemodialysis. Invest Ophthalmol. 1964; 3: 273–284.
De Marchi S, Cecchin E, Tesio F. Intraocular pressure changes during hemodialysis: prevention of excessive dialytic rise and development of severe metabolic acidosis following acetazolamide therapy. Renal Failure. 1989; 11: 117–124.
Watson AG, Greenwood WR. Studies on the intraocular pressure during hemodialysis. Canad J Ophthalmol. 1966; 1: 301–307.
Cecchin E, De Marchi S, Tesio F. Intraocular pressure and hemodialysis. Nephron. 1986; 43: 73–74.
Afshar R, Ghasemi H, Shabpiray H et al. Monitoring of intraocular pressure and its correlation with systemic parameters before and after hemodialysis. Iran J Kidney Dis. 2013; 7: 53–59.
Hu J, Bui KM, Patel KH et al. Effect of hemodialysis on intraocular pressure and ocular perfusion pressure. JAMA Ophthalmol. 2013; 131: 1525–1531.
Foster PJ, Buhrmann R, Quigley HA, Johnson GJ. The definition and classification of glaucoma in prevalence surveys. Br J Ophthalmol. 2002; 86: 238–242.
Figure 1
 
SDOCT (enhanced depth imaging) image showing measurement of macular ChT at the subfovea, and 0.5, 1, and 1.5 mm nasal and temporal to the fovea, respectively.
Figure 1
 
SDOCT (enhanced depth imaging) image showing measurement of macular ChT at the subfovea, and 0.5, 1, and 1.5 mm nasal and temporal to the fovea, respectively.
Figure 2
 
Illustration of the change in IOP, osmolality, and ChT at 30 and 60 minutes following the WDT in FE-APAC subjects.
Figure 2
 
Illustration of the change in IOP, osmolality, and ChT at 30 and 60 minutes following the WDT in FE-APAC subjects.
Figure 3
 
Illustration of the change in IOP, osmolality, and ChT at 30 and 60 minutes following the WDT in PACG subjects.
Figure 3
 
Illustration of the change in IOP, osmolality, and ChT at 30 and 60 minutes following the WDT in PACG subjects.
Figure 4
 
Illustration of the change in IOP, osmolality, and ChT at 30 and 60 minutes following the WDT in normal subjects.
Figure 4
 
Illustration of the change in IOP, osmolality, and ChT at 30 and 60 minutes following the WDT in normal subjects.
Table 1
 
Baseline Characteristics of Study Subjects
Table 1
 
Baseline Characteristics of Study Subjects
Table 2
 
Comparison of Changes in Parameters of Angle Closure Subjects at 30 and 60 Minutes After the WDT
Table 2
 
Comparison of Changes in Parameters of Angle Closure Subjects at 30 and 60 Minutes After the WDT
Table 3
 
Comparison of Changes in Parameters Between Angle Closure Subtypes and Normals at 30 and 60 Minutes After the WDT
Table 3
 
Comparison of Changes in Parameters Between Angle Closure Subtypes and Normals at 30 and 60 Minutes After the WDT
Table 4
 
Factors Associated With Change of Mean ChT From Baseline to 30 Minutes After the WDT
Table 4
 
Factors Associated With Change of Mean ChT From Baseline to 30 Minutes After the WDT
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