In Reply: The Quantitative Measurements of Vascular Density and Flow Area of Optic Nerve Head Using Optical Coherence Tomography Angiography
We read with interest the correspondence by Najafi on our recent paper. First, we would like to thank the author of this correspondence for his interest to our paper. Dr Najafi has correctly mentioned that he agrees with us that for the majority of advanced or moderately advanced glaucoma, optic disc changes can be highly suggestive in making the diagnosis. We are aware of the important methodological issues in our study. That is why we clearly defined and explained measurement of the outcome in the material and method section in our manuscript. It is crucial to know that as far as definition and measurement of a variable clearly mentioned in the material section and reported result is consistent with the mentioned definition, methodological issues cannot be raised.1,2 Second, Dr Najafi has mentioned that small sample size in 2 age categories in our study can cause deviation from normative, which is a common mistake. Considering different sampling methods in clinical researches, it is important to know that small sample size cannot be a reason for deviation from normative. Actually correct sampling method is more important than sample size.1,2 A big sample size with wrong sampling method can easily lead to deviation from normative database; however, small sample size considering correct sampling method can be a good representative of the population. Therefore, sample size and sampling method are 2 completely different methodological issues which should not be confused with each other.1,2
Dr Najafi has also mentioned that inclusion of subject with refractive error creates a selection bias. Having more than 200 types of bias in clinical researches, it is the responsibility of the careful readers to not simply judge about this methodological issue. We strongly recommend that clinical researchers be more familiar with methodological issues by reading the below mentioned references.
After carefully assessing this feedback, we believe that our results do not need to be modified, and they support the conclusion of our paper regarding a normative database for perfusion of the optic disc in healthy people from the second to the seventh decades of life.