This study evaluated the feasibility of using the SOCT to determine subfoveal CT in vivo. The coefficients of variability, repeatability, and reproducibility obtained in this study were comparable to those obtained in studies where the retinal thickness was measured, which indicates that the SOCT may be used for the calculation of CT in vivo. Additionally, in the small sample of participants evaluated, the thickness of the subfoveal choroid was found to correlate significantly with AL.
Six macular radial scans (based on previous OCT studies assessing the repeatability of the retinal thickness measurement14,15) were taken per participant, each of which in turn comprised 15 radial line scans. This resulted in a total of 90 images analyzed per subject. The radial scans were 7 mm in length arranged in a star-like pattern with the center on the fovea and spaced 12° from each other. The coefficients of variability, repeatability, and reproducibility were 0.80%, 2.97%, and 2.44% respectively, with an ICC of 99%, which were comparable with past retinal articles that reported good between session and within-session indices of reproducibility and repeatability (CoR: 0.89% to 1.51%, CoRepro 1% to 6%).14,15 However, the interest in the measurement of CT is so recent that limited data is available from healthy subjects to allow comparison with this study. The average subfoveal CT described in past articles ranged from 287 ± 76 (no ethnicity specified)1 to 354 ± 111 μm (Japanese subjects)10 and used EDI OCT and high penetration OCT, respectively. This study describes an average estimation of subfoveal CT of 448.48 ± 81.99 μm in younger healthy Caucasians (20 to 49 years old), which is hypothesized to be due to the negative relationship reported between age and subfoveal CT in healthy subjects.1,10 Because of the limited number of publications available on normative data for the measurement of subfoveal CT, this study also used a Bland-Altman plot to provide an additional qualitative way of analyzing the between-visit reproducibility of the instrument. None of the measurements fell outside the upper and lower limits in the graph after assessing the width of the 95% confidence interval, which agrees with the good coefficients previously discussed.
The results of the present article additionally describe a significant correlation between subfoveal CT and AL such that macular CT decreased with increasing AL. However, caution should be exercised when interpreting the findings because of the small sample size evaluated. AL is known as an important structural correlate in eye growth and myopia16–22 and one of the predictive factors, among others such as age and ethnicity, of the retinal nerve fiber layer thickness measured using OCT.23,24 Both children and adults exhibit significantly thinner macula with increasing AL,25–27 and AL has also very recently been found to correlate with the height of the posterior staphyloma in highly myopic patients.9 The present study was limited by the low number of subjects, the relatively low range of prescriptions included as well as the manual nature of the calculations. Consequently, a larger study is necessary to verify and validate our observation.
From a clinical perspective, it is important to highlight the increasing role that the OCT might play in the diagnosis and management of retinal disease in future practice28 because of its ability to quantify CT in vivo and non-invasively.12
In summary, the coefficients of variability, repeatability, and reproducibility obtained in this pilot study, suggest that it is feasible to measure the subfoveal CT in vivo manually. Future advancements with automated calculations of CT would improve the technique and would facilitate the possibility to generate studies where the choroidal biometry in human eyes could be monitored. It is, therefore, proposed that OCT could be a useful instrument to perform in vivo assessment and monitoring of CT changes with eye growth and retinal disease in the human eye.
We thank William Bourassa Jr, for his invaluable graphics assistance.
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