Choroidal Modulations Following Water Drinking Test (WDT) as Measured Using Swept-source Optical Coherence Tomography (SS-OCT)

Abstract

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]. Studies have shown the choroid’s ability to modulate its thickness is based on defocused retinal imagery, with an increment of thickness upon myopic defocus and vice versa^{[2, 3]}. Observation of choroidal thickness (CT) over time allows the study of the layer’s modulation which may be deemed a vital inspection of ocular responses in ocular growth and refractive changes^{[4, 5]}.

 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 water drinking test (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^[8-10]. 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.