Choroidal Thickness Changes During Systemic Hypercapnia and Hyperoxia

Abstract

Purpose: : A preliminary study to evaluate choroidal thickness under hypercapnic and hyperoxic conditions in healthy subjects.

Methods: : Three healthy subjects aged 22, 23 and 27 years with refractive error less than ± 6.00 DS and/or ± 2.50 DC, no ocular or systemic disease, and no medications, were recruited for the study. Each underwent spectral domain (SD)-OCT (Spectralis HRA-OCT; Heidelberg Engineering, Germany) imaging using the standard macular volume scan (1, 3, 6 mm ETDRS, 25 X 25 degrees) and RNFL thickness scan at baseline, and during hypercapnic (P_ETCO₂ = 15% increase) and hyperoxic (P_ETO₂ = 500 mm Hg) provocations. All subjects breathed via a commercial sequential gas delivery circuit (Respiract, Thornhill Inc., Toronto, ON, Canada). Each respiratory condition was maintained for 10 minutes and scanning occurred only once P_ETCO₂ and P_ETO₂ had stabilised. Choroidal thickness maps were produced using custom software (HRA/Spectralis Version alpha v.5.3.2) by adjusting the boundary lines to delineate the retinal pigment epithelium basement membrane and the choroid/scleral boundary.

Results: : No significant change in average choroidal thickness was found under hyperoxic or hypercapnic conditions in the macular or optic nerve head region. Average macular choroidal thickness at baseline was 248.4 microns and under hypercapnic and hyperoxic conditions was 248.1 and 255 .2 microns, respectively. Average choroidal thickness in the optic nerve head region measured at baseline, under hypercapnia and hyperoxia was 129.3, 128.6 and 129.1 microns, respectively.

Conclusions: : The choroid in healthy retina does not vary significantly in thickness under hypercapnia or hyperoxia provocations.

Keywords: choroid • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • imaging/image analysis: clinical