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The authors present an MRI study including 61 MRI scans using a 1.5 T with slice thickness of 1 or 5mm and the sequence showing the highest resolution of the chiasm. A predetermined set of measurements were taken in a step-by-step order, with normal distribution assessed using Shapiro-Wilk test on all measurements. The age range of participants was 20-78 years (mean 50.3). Both the mean width and offset of the chiasm were found to have a normal distribution, with the mean measurements being 12.0mm and 4.7mm respectively. None of the included participants were found to have a pure X shaped chiasm, but rather appear to be H shaped. The authors believe this study is the first report of the mean inclination of the chiasm relative to the anterior and posterior commissures line of 25.1 degrees. When comparing the different sequences, the authors noted interestingly that T1 sequences returned significantly narrower chiasms than T2 sequences. Limitations including the small sample size, scan thickness resulting in partial voluming and the examination of the chiasm in only one plane. The authors argue that a future study with a larger sample size and using thin-slice MRI images to investigate the relationship of the chiasm to other structures is needed. This study increases knowledge regarding the anatomy variation of the optic chiasm.

Variation in the anatomy of the normal human optic chiasm: an MRI study.
Bosler NSI, Ashton D, Neely AJ, Lueck CJ.
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Lauren R Hepworth

University of Liverpool; Honorary Stroke Specialist Clinical Orthoptist, Northern Care Alliance NHS Foundation Trust; St Helen’s and Knowsley NHS Foundation Trust, UK.

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