We thank Drs He and Huang for their interest in our study. In their letter, Dres He and Huang point out that a previous study in contrast to our investigation showed that subfoveal choroidal thickness was significantly thicker in eyes (n = 18) at 57.2 ± 26.9 months after an acute nonischemic anterior ischemic optic neuropathy than in eyes of a control group (n = 28). In the same study, subfoveal choroidal thickness increased with longer follow-up after the event ( P = .047; correlation coefficient r = 0.46). Taking into account the mean follow-up of 57.2 months and extrapolating the regression line of the association between subfoveal choroidal thickness and follow-up time as shown on Figure 3 in the article, one arrives at a subfoveal choroidal thickness of about 190 μm at the time when the nonischemic anterior ischemic optic neuropathy occurred. That is approximately the same value or even thinner than the value we found in our study on patients with an acute nonischemic anterior ischemic optic neuropathy (subfoveal choroidal thickness: 207 ± 55 μm). Both values of subfoveal choroidal thickness, the one of the previous study (approximately 190 μm) and the one of our study (207 ± 55 μm), are thinner than the mean value of subfoveal choroidal thickness (254 ± 107 μm) found in a population-based study on 3233 Chinese individuals after adjustment for age and refractive error. Similar measurements of subfoveal choroidal thickness as in the study on Chinese subjects were found in investigations on individuals of other ethnicity. One may therefore infer that the previous study and our study both agree in that eyes with an acute non-arteritic anterior ischemic optic neuropathy have a thinner subfoveal choroid as compared to normal eyes.
Drs He and Huang additionally mention that choroidal thickness may depend on ocular systemic parameters such as intraocular pressure, blood pressure, smoking, hypercholesterolemia, diabetes mellitus, and use of some dyslipidemia. Since we did not adjust for these parameters in our study, Drs He and Huang discuss that the thin subfoveal choroid detected in the patients of our study might have been attributable to underlying systemic diseases and might not have primarily been associated with the acute non-arteritic anterior ischemic optic neuropathy. In contrast to the remark by Drs He and Huang, large population-based studies such as the Beijing Eye Study did not detect strong associations between subfoveal choroidal thickness and the parameters mentioned. One may therefore assume that the marked difference in subfoveal choroidal thickness between patients with acute non-ischemic optic neuropathy and normal individuals may not have been markedly influenced, if at all, by underlying diseases.
We completely agree with Drs He and Huang in that it had been better to use axial length instead of refractive error to adjust the measurements of subfoveal choroidal thickness.