December 2010
Volume 51, Issue 12
Letters to the Editor  |   December 2010
Author Response: GEN Is Not HGN
Author Affiliations & Notes
  • Chad A. Whyte
    JFK Hospital, Edison, New Jersey.
  • Michael Rosenberg
    JFK Hospital, Edison, New Jersey.
Investigative Ophthalmology & Visual Science December 2010, Vol.51, 6901. doi:10.1167/iovs.10-6537
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      Chad A. Whyte, Michael Rosenberg; Author Response: GEN Is Not HGN. Invest. Ophthalmol. Vis. Sci. 2010;51(12):6901. doi: 10.1167/iovs.10-6537.

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      © ARVO (1962-2015); The Authors (2016-present)

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We are sorry that Dr. Citek is “deeply troubled” by the peer review of our paper. 1 The review was conducted by two reviewers, both of whom took time to evaluate four drafts of the paper before the final acceptance. 
The title of Dr. Citek's letter “GEN Is Not HGN” suggests that his difficulties with our paper on physiologic gaze-evoked nystagmus had more to do with his involvement with the HGN test than with our paper itself. There is no physiological difference between horizontal gaze-evoked nystagmus and horizontal gaze nystagmus. 
The erroneous number of subjects per decade appeared in the online prepublication version of the article and was corrected in the print version. 
This study was performed specifically to evaluate the incidence of horizontal gaze nystagmus in normal subjects of different ages. We found that there was clear recordable nystagmus at smaller gaze angles, with amplitudes well within the recording limits of our system in a significant number of normal subjects. This finding suggested to the reviewers that a more detailed look at physiological gaze-evoked nystagmus at these angles would be important in judging the limitations of the HGN test. We concurred. 
Dr. Citek comments that we made no reference to any “accepted peer-reviewed literature that supports the horizontal gaze nystagmus test.” We also did not reference any of the ample literature that documents the high false-positive rate of the test. Had we done either, the reviewers, we suspect, would have rightfully noted that these references should be removed, as they don't have anything to do with the study itself. 
We agree that the nystagmus amplitudes quoted in the paper are small compared with those in other studies. As noted in the paper, the method used to calculate the amplitude would result in smaller values than other methods. The program written to identify the beats of nystagmus looked at velocities of the fast and slow phases. The algorithm clipped the extremes of the movements, to get the best estimate of the velocities of both the slow phases and the quick phases. We did not write an additional program to best determine the true amplitudes of nystagmus beats, as it was not critical to the original purpose of the project. 
Clearly, this article does not prove that the HGN test is not valuable. As Dr. Citek noted, we did not evaluate the incidence of visually detectable nystagmus at different gaze angles. Our findings suggest that such a study would be worthwhile. 
Whyte CA Petrock AM Rosenberg M . Occurrence of physiologic gaze-evoked nystagmus at small angles of gaze. Invest Ophthalmol Vis Sci. 2010;51:2476–2478. [CrossRef] [PubMed]

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