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The Area under the Main Sequence as an Alternative Method to Measure Saccadic Dynamics

Busettini, Claudio, PhD1*; Braswell Christy, Jennifer, PT, PhD2

doi: 10.1097/OPX.0000000000001299
ORIGINAL INVESTIGATIONS

SIGNIFICANCE This study shows that the area under the main sequence (MSAREA) is a valid alternative to the standard peak-velocity main sequence in measuring saccadic dynamics. A one-parameter area model, MSAREA = G PW = 1.55 × SACSIZE1.55, with SACSIZE as the size of the saccade, 1.55 as a power factor, and G PW = 1.55 as a gain parameter, is presented.

PURPOSE SACPEAK = V max × (1 − e −SACSIZE/SAT) is the traditional model used to describe the saccadic main sequence, the relationship between the size of the movement and its peak velocity (SACPEAK). In the previous article, we have shown that there is a strong linear correlation between the two parameters V max and SAT, which severely affects the model's clinical applicability. The purpose of this study is to see if, by using the MSAREA as an alternative approach, we can overcome the limitations of the traditional model.

METHODS Participants and main sequence data are the same as the previous study. A trapezoidal integration was used to estimate the MSAREAs as a function of SACSIZE.

RESULTS A two-parameter area model was computed to determine the range of variability of its parameters and R 2 values. These were then used as reference values in the search for one-parameter alternatives. The one-parameter model MSAREA = G PW = 1.55 × SACSIZE1.55 performed well for all data sets. We tested its validity by performing a comparison with other one-parameter area models.

CONCLUSIONS Area models are superior to peak-velocity models in terms of R 2 and stability and can be reduced to robust one-parameter expressions with only limited degradation in R 2. This not only greatly simplifies the determination if a set is inside or outside a reference population but also allows for direct comparisons between sets, with the saccadic dynamics expressed by a simple linear gain factor (G PW = 1.55).

1Department of Optometry and Vision Science and Vision Science Research Center, University of Alabama at Birmingham, Birmingham, Alabama

2Department of Physical Therapy, University of Alabama at Birmingham, Birmingham, Alabama *cbus@uab.edu

Submitted: September 16, 2017

Accepted: June 19, 2018

Funding/Support: UAB Health Service Foundation General Endowment Fund; National Eye Institute (P30 EY-03039 Vision Science Research Center Core grant); and Alabama Department of Commerce.

Conflict of Interest Disclosure: None of the authors have reported a financial conflict of interest.

Author Contributions and Acknowledgments: Conceptualization: CB, JBC; Data Curation: CB, JBC; Formal Analysis: CB, JBC; Funding Acquisition: CB; Investigation: CB, JBC; Methodology: CB, JBC; Project Administration: CB; Resources: CB, JBC; Software: CB; Supervision: CB, JBC; Validation: CB, JBC; Visualization: CB, JBC; Writing – Original Draft: CB, JBC; Writing – Review & Editing: CB, JBC.

The authors would like to thank Drs. James Johnston, Katherine Weise, and Mark Swanson for their assistance as members of the UAB VOR Clinic and Dr. Kevin Schultz for the helpful discussions and review of the manuscript.

© 2018 American Academy of Optometry