We thank Dr Çalışkan and his co-workers for their beneficial comments.1
Distribution of all retrobulbar blood flow variables was normal except in superior ophthalmic vein (SOV) maximal blood, which had a P value of 0.041 in the Kolmogorov−Smirnov test. However, using Mann−Whitney U-test did not change the result (P=0.008).
Although the equality of variances is an assumption of ANCOVA, it should hold for the residual of this regression model (after adjustment for the confounder variables). However, it has been shown that ANCOVA would obtain the correct type I error even with unequal sample size. Indeed, the estimator of the effect at the observed mean is not different between equal and unequal variance assumptions.2 Also, we used type III sum of squares, which is more robust in obtaining the variance of treatment effect.
In our subjects, all vessels were successfully detected except one SOV in smokers. These vessels have normal anteroposterior flow. Some of the previous studies did not mention a reverse flow in orbital vessels in thyroid eye disease (TED).3, 4 However, undetectable SOV in a patient may be attributed to more reduced blood flow. Furthermore, high percentage of reverse flow in the SOV of patients with TED was observed in dysthyroid optic neuropathy.5 Thus, in our study, lack of reverse retrobulbar blood flow might probably be the result of having no patients with dysthyroid optic neuropathy or other most severe forms of TED.
Çalışkan S, Acar M, Gürdal C . Comment on: ‘Effect of smoking on retrobulbar blood flow in thyroid eye disease’. Eye 2016. e-pub ahead of print 16 December 2016; doi:10.1038/eye.2016.292.
Funatogawa I, Funatogawa T . Analysis of covariance with pretreatment measurements in randomized trials: comparison of equal and unequal slopes. Biom J 2011; 53 (5): 810–821.
Konuk O, Onaran Z, Ozhan Oktar S, Yucel C, Unal M . Intraocular pressure and superior ophthalmic vein blood flow velocity in Graves' orbitopathy: relation with the clinical features. Graefe's Arch Clin Exp Ophthalmol 2009; 247 (11): 1555–1559.
Yanik B, Conkbayir I, Acaroglu G, Hekimoglu B . Graves' ophthalmopathy: comparison of the Doppler sonography parameters with the clinical activity score. J Clin Ultrasound 2005; 33 (8): 375–380.
Nakase Y, Osanai T, Yoshikawa K, Inoue Y . Color Doppler imaging of orbital venous flow in dysthyroid optic neuropathy. Jpn J Ophthalmol 1994; 38 (1): 80–86.
The authors declare no conflict of interest.
About this article
Cite this article
Sadeghi-Tari, A., Jamshidian-Tehrani, M., Nabavi, A. et al. Reply to: ‘Comment on: Effect of smoking on retrobulbar blood flow in thyroid eye disease’. Eye 31, 814–815 (2017). https://doi.org/10.1038/eye.2016.291