Spatial Distribution of Posterior Pole Choroidal Thickness by Spectral Domain Optical Coherence Tomography

The choroid, a vascular meshwork between the retina and sclera, plays a major role in providing oxygen and nutrition to the outer layers of the retina.1 In recent years, increased awareness of its role in ocular development and its known association with many diseases of the posterior pole have stimulated a renewed focus on understanding choroidal anatomy and physiology.2 A number of methods, including histology3 and ultrasonography,4 have previously been used to quantify choroidal thickness (CT); however, the overall precision of these approaches is still lacking. Fortunately, the recent introduction of spectral domain optical coherence tomography (SD-OCT) and the description of “enhanced depth imaging” scanning protocols have afforded a new opportunity to improve the accuracy of quantitative choroidal assessment. As a result, changes in CT have now been studied using different OCT technologies over a wide range of ocular pathologies (e.g., glaucoma,5 inherited retinal diseases,6 high myopia,7 central serous chorioretinopathy,8 polypoidal choroidal vasculopathy,9 neovascular age-related macular degeneration [AMD],9 and Vogt Koyanagi Harada disease10). Although the use of OCT has provided many new insights into choroidal morphology, to date there exists a notable disparity between the CT measurements obtained in different studies. For example, several studies on the cross-sectional variation of CT measurements in “normal” subjects have shown CT to be greatest at the fovea, with decreasing thickness more nasally than temporally.9,11,12 Other results suggest that the foveal CT is thinner than the choroid superior to the fovea.13 These discrepancies may arise due to the use of different image acquisition methodologies, a generally limited field of view for scanning, and inconsistencies in choosing the exact locations for repeated CT measurement. Regardless, the exact spatial distribution of CT changes in the macular region of human eyes remains unclear. In addition, most OCT-derived studies have focused on assessment of CT in the macular region alone, examining the correlation between macular CT changes and disease expression. However, unlike the neurosensory retina, a complex and highly organized neural structure with the fovea as its unmistaken center, the choroid is a vascular layer with a potentially very different topography. Determination of choroidal spatial distribution may thus be difficult, and potentially inaccurate, in the context of macular scanning alone. In this report, we aim to address these issues by obtaining larger, two-dimensional (2D) maps of the spatial distribution of the choroid in the posterior pole and identifying its specific patterns in healthy volunteers using SD-OCT.