Dear Editor,
We appreciate the thoughtful comment by Yuwan Gao concerning our paper on optic nerve kinking [1]. We agree the 57 normal tension glaucoma (NTG) patients do not represent a large cohort of NTG patients. Nevertheless, it represents the largest radiological study ever performed in this condition. Concerning the variability between radiological methods, there is data that demonstrates a high congruence between computed tomography (CT) and magnetic resonance imaging (MRI), whereas ultrasound, which we did not use in our study, is less reproducible [2]. We don’t agree that we did not describe explicit criteria for the definition of kinking as we used the following criteria: optic nerve kink: 0 = straight or slightly curved optic nerve, 1 = visible kink of the optic nerve in axial images (1.1 = 1 kink, 1.2 = two kinks), 2 = visible kink of the optic nerve in sagittal images (2.1 = 1 kink, 2.2 = two kinks), 3 = visible kink of the optic nerve in both, axial and sagittal, images. In addition, to mitigate bias in retrospective data collection, all radiological images were reviewed by two experienced neuro-radiologists and one experienced neuro-ophthalmologist blinded to whether the subject was NTG or control. It should be noted that kinking in the vertical plane was virtually absent in the control group. Further, we did not discuss whether kinking is an anatomical predisposition or the result of NTG. This question was not the subject of this study and will be the subject of a future paper. Our suggestion that kinking alters fluid dynamics has already been established in a review on twisted blood vessels [3]. We consciously did not include multivariant analysis, since such analysis only answers the question concerning correlation and never the question for causation [4] but we fully support that larger studies should be performed and would gladly offer our cooperation. The purpose of our current study was to demonstrate a radiological feature and not to elaborate on its origin.
Competing interests
The authors declare no competing interests.
Footnotes
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References
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