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Seasonality of births in horizontal strabismus: comparison with birth seasonality in schizophrenia and other disease conditions

Published online by Cambridge University Press:  22 March 2019

A. B. Agarwal
Department of Physiology & Cell Biology, University of Nevada, Reno School of Medicine, Reno, NV, USA
K. Cassinelli
Sierra Eye Associates, Reno, NV, USA
L. A. Johnson
Department of Physiology & Cell Biology, University of Nevada, Reno School of Medicine, Reno, NV, USA Sierra Eye Associates, Reno, NV, USA
K. Matsuda
Matsuda Eye Clinic, Sennan, Osaka, Japan
B. Kirkpatrick
Department of Psychiatry & Behavioral Sciences, University of Nevada, Reno School of Medicine, Reno, NV, USA
W. Yang
School of Community Health Sciences, Nevada Center for Health Statistics and Informatics, University of Nevada, Reno, NV, USA
C. S. von Bartheld
Department of Physiology & Cell Biology, University of Nevada, Reno School of Medicine, Reno, NV, USA
E-mail address:


Recent work has implicated one type of horizontal strabismus (exotropia) as a risk factor for schizophrenia. This new insight raises questions about a potential common developmental origin of the two diseases. Seasonality of births is well established for schizophrenia. Seasonal factors such as light exposure affect eye growth and can cause vision abnormalities, but little is known about seasonality of births in strabismus. We examined birth seasonality in people with horizontal strabismus in a retrospective study in Washoe County, Nevada, and re-examined similar previously obtained data from Osaka, Japan. We then compared seasonal patterns of births between strabismus, refractive error, schizophrenia and congenital toxoplasmosis. Patients with esotropia had a significant seasonality of births, with a deficit in March, then increasing to an excess in September, while patients with exotropia had a distinctly different pattern, with an excess of births in July, gradually decreasing to a deficit in November. These seasonalities were statistically significant with either χ2 or Kolmogorov–Smirnov-type statistics. The birth seasonality of esotropia resembled that for hyperopia, with an increase in amplitude, while the seasonality for myopia involved a phase-shift. There was no correlation between seasonality of births between strabismus and congenital toxoplasmosis. The pattern of an excess of summer births for people with exotropia was remarkably similar to the well-established birth seasonality of one schizophrenia subtype, the deficit syndrome, but not schizophrenia as a whole. This suggests a testable hypothesis: that exotropia may be a risk factor primarily for the deficit type of schizophrenia.

Original Article
© Cambridge University Press and the International Society for Developmental Origins of Health and Disease 2019 

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