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Hannah Burfield, Ashutosh Jnawali, Nimesh Bhikhu Patel, Lisa A Ostrin; Retinal and Choroidal Thickness Measurements – Repeatability and Influence of Axial Length. Invest. Ophthalmol. Vis. Sci. 2017;58(8):4434. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
The choroid is a dynamic vascular structure that has been implicated in eye growth regulation and myopia development. Evidence suggests that the choroid modulates thickness in response to defocus and chromatic cues, and may differ in emmetropic and myopic individuals. The goal of this study was to evaluate choroidal thickness across the posterior pole and examine the relationship with axial length.
Right eyes of 30 subjects (ages 21-40) were imaged with spectral domain optical coherence tomography (SD-OCT) using six 30° radial scans centered at the fovea. All measurements occurred between 9:00-10:00 am, and were repeated at the same time within two weeks. Following OCT, cycloplegic autorefraction and axial length (AL) were measured. OCT images were analyzed using a custom written program in Matlab after adjusting for lateral magnification. Scans were segmented for the inner limiting membrane, Bruch’s membrane and posterior choroid. Retinal (RT) and choroidal thickness (CT) were determined for the fovea and subfovea, central 1mm diameter, and 3mm and 6mm annular rings.
Emmetropic subjects (n=14, SE 0 ± 0.4 D,) had a central RT of 219.7 ± 17.8 μm and CT of 382.4 ± 81.6 μm, and myopic subjects ( n=16, -3.6 ± 1.9 D) had a central RT of 225.1 ± 20.6 μm and CT of 307.7 ± 78.6 μm, respectively. Regression analyses showed that foveal RT increased with AL (p < 0.05); however, 1mm, 3mm, and 6mm regions were not correlated. Subfoveal CT, 1mm diameter, and 3mm and 6mm annuli significantly decreased with increasing AL and myopic refraction (p < 0.05 for all). For all subjects, the retina was thickest in the superior and nasal regions, and the choroid was thickest in the temporal and inferior regions. Bland-Altman analyses revealed an average difference of -1.4 ± 16.5 µm for subfoveal CT and 0.6 ± 3.9 µm for foveal RT.
Results show that the choroid is significantly thinner with longer axial length, including central and peripheral regions. Retinal thickness significantly increased with longer axial length in the foveal region only. Differences in CT and RT with axial length could be a consequence of biomechanical or developmental changes. SD-OCT was shown to be capable of wide-field retinal and choroidal imaging with good repeatability, and can be further used to examine the role of the choroid in eye growth and myopia development.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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