Ayob, Aina Afiqah and Mohamad Ares, Nur Diyana and Abdul Rahman, Nur Syahirah and Zahari, Ilyanoon and Abdul Rahim, Muhammad Afzam Shah and Yusof @ Alias, Firdaus
(2025)
Choroidal modulations following water drinking test (WDT) as measured using Swept-source Optical Coherence Tomography (SS-OCT).
Asian Journal of Medicine and Biomedicine, 9 (S1).
pp. 12-14.
E-ISSN 2600-8173
Abstract
The ocular choroidal layer was previously difficult to study due to its location sandwiched between the sclera and retina. Advancements in imaging technology, particularly the Swept-source Optical Coherence Tomography (SS-OCT) enabled the in vivo measurement of deep-ocular structures such as the choroid[1]. The choroid is the most vascularized tissue in the eye which mainly functions to supply oxygen to the retina[2]. The water drinking test (WDT) compares the intraocular pressure (IOP) before and after a certain amount of water is consumed, allowing for the estimation of peak circadian IOP[3]. The physiology behind the WDT is not fully understood, however, the choroidal volume's abrupt expansion was the reason for the reported IOP elevations[4, 5]. Additionally, a prospective investigation examining the alterations in choroidal circulation and structure came to the conclusion that the dilatation of the choroidal arteries was directly responsible for the increase in thickness following the WDT[8]. The purpose of this study was to use SS-OCT to investigate changes in choroidal thickness (CT) following the WDT.
This study evaluated the effect of water drinking on CT using the SS-OCT in healthy young adults. Eighteen young adults (22.61±0.78 years; 9 females) were recruited into the study, after obtaining their written consent. Participants ingested 1000ml of water within 5 minutes as per the WDT protocol[6, 7]. The macular and peripapillary (area around the optic disc, OD) CTs were measured using the Deep Range Imaging (DRI) Topcon SS-OCT Triton Series system (Topcon Inc., Tokyo, Japan) at baseline and after 5, 10, 15, 30, 45, 60, 75, and 90 minutes of WDT. Intraocular pressure (IOP) was measured at the various time points using a non-contact tonometer (Keeler, United Kingdom). A 3D macula protocol imaging of 7.0×7.0mm raster scan was used for macular CT measurement while a 3D 12x12mm radial scan centered on OD was used for peripapillary CT measurement. Only scans with a signal strength index ≥60 were included. The distance between the Bruch’s membrane and the choroid-scleral interface was taken as CT. The CTs were compared between the time points to evaluate the choroidal modulations using repeated measures of analysis of variance (RM-ANOVA). Post-hoc analyses were conducted using the Bonferroni correction.
The IOP peaked from 15.56±3.28mmHg at baseline to 17.56±3.29mmHg at 10 minutes post water ingestion (Bonferroni correction, p=0.02), before reducing to a plateau of 14.72±2.85mmHg after 75 minutes post-WDT. This observation was similar to other studies[4, 8, 9]. The average baseline CTs were 247.79±55.07μm and 299.50±102.46μm in the macular and peripapillary, respectively. No significant choroidal modulations were evident in any macular zones (RM-ANOVA, p>0.05) (Table 1). The temporal peripapillary zone showed choroidal modulations (RM-ANOVA, p=0.001) (Table 2), where the 60-minute CT recorded a significant increment relative to the baseline (Bonferroni correction, p=0.05).
The choroid at the macular zones showed no modulations upon WDT, despite the increase in IOP. The peripapillary choroid at the temporal zone of OD showed modulations following WDT, with its CT retained swollen even after 60 minutes post-WDT. The choroidal vasculature of healthy young adults exhibits an autoregulatory mechanism over the changes in perfusion and ocular pressure. Sectoral modulations in the peripapillary choroid, concerning WDT, necessitate further testing such as on different refractive groups to rule out the possibility of a refractive effect on CT changes.
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