Potential Sampling Bias in Investigation of Upright-Supine Test for Vertical Strabismus—Reply

In Reply We appreciate Dr Bhatti's interest in our article¹ and thoughtful comments. Defining skew deviation merely by nonconformity to fourth nerve palsy (4NP) and presumed posterior fossa localization, while practical, would decrease case ascertainment by potentially including partial third nerve palsy (which would show vertical misalignment, presumed posterior fossa localization, and nonconformity to the 4NP pattern), mechanical or extraocular muscle pathology (if the presumed localization is incorrect), or other misclassified pathophysiologies. Perhaps our definition is overly rigid in requiring magnetic resonance imaging correlations, but this increases specificity, which is important for the validation of a comparative diagnostic tests.