Effect of temperature on the thickness of the ocular choroid

Abstract

Significance: Cooling the anterior eye significantly increased the thickness of the choroid, indicating that the choroid has the capacity to modulate its thickness in response to locally induced temperature changes, among many other factors. Purpose: The choroid of the eye is implicated in thermoregulation of the retina, however, little is known about this function. The purpose of this study was to investigate the effect of surface temperature changes of the anterior eye on the thickness of the choroid. Methods: In 20 healthy subjects (14 females, age: 23 ± 3 years), one eye was cooled and the other eye simultaneously warmed for 10 minutes using heat/ice packs applied to the closed eyes, and the eyes were allowed to recover for 15 minutes. Eyelid temperatures were continuously monitored with thermal probes, and chorioretinal images were taken in both eyes using Optical Coherence Tomography (OCT) before and after heating/cooling, and then at every 5 minutes. Changes in choroidal and retinal thicknesses were compared between the cooled and the warmed eye. Results: Following the application of heat/ice packs, there was a significant difference in temperature changes between the cooled eye and the warmed eye at every time point (all p < .001), with a maximum difference in temperature of 15.85 °C between the cooled and the warmed eyes. Macular choroidal thickness in the cooled eye increased significantly after 10 minutes (mean difference (post-pre) [95% CI] = +3.78 µm [+1.07 to +6.89], t19= 2.42, p = .026), and rapidly diminished during the recovery, with no change in the warmed eye (-1.65 µm [-3.63 to +0.49] t19 = -1.56, p = .135). There was a significant difference in changes of macular choroidal thickness between the cooled and the warmed eye (+5.43 µm [+1.93 to +8.92], t19 = 3.25, p = .004). The choroid also showed significant thickness increase in parafoveal (+7.03 µm [+1.65 to +12.41], p =.013) and perifoveal (+5.26 µm [+1.69 to +8.83], p=.006) regions in the cooled eye relative to the warmed eye. However, there were no changes in retinal thickness with either cooling (+0.00 µm [-0.638 to +0.639], t19 = 0.001, p = .999) or warming (+0.38 µm [-0.65 to +1.42], t19 = 0.77, p = .450) of the anterior eye. Conclusions: Cooling the anterior eye caused a small but significant increase in choroidal thickness, whereas warming the eye did not affect the thickness. The OCT measures of retinal thickness did not change with either cooling or warming, indicating that the choroidal thickness changes were not attributable to OCT artefacts potentially induced by temperature changes. Our study findings suggest that the choroid modulates its thickness rapidly and transiently in response to local temperature changes, but the mechanism of these responses remains to be investigated.