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Michael Paul Masters, Emiliano Bruner, Sarah Queer, Sarah Traynor, Jess Senjem; Analysis of the volumetric relationship among human ocular, orbital and visual cortical anatomy. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):898.
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© ARVO (1962-2015); The Authors (2016-present)
Recent research on the visual system has examined the volumetric relationship among the eye, orbit, and visual cortex in humans. Some studies have also suggested that light levels may drive eye size, which was hypothesized to in turn dictate orbital and visual cortical size, as a product of adapting or acclimating to differences in available daylight at disparate latitudes. However, further research is necessary in order to establish how these variables are related, and to what extent ocular volume influences orbital and visual cortical volume in humans.
Relationships among these anatomical components were investigated using MRIs from a large sample of 83 individuals, which also included each subject’s height, age, sex, and uncorrected visual acuity scores. Frontal and occipital gyri volumes were calculated using two different cortical parcellation tools, Brain Parser 56 ROI and FreeSurfer 5.3.0, in order to provide a better understanding of how the eye and orbit vary in relation to the visual cortex, and in association with cerebral gyri of the frontal cortex that are not directly related to vision.
Results indicated that ocular and orbital volumes were weakly correlated, but that eye volume explains only 14.7% of the variance in orbital volume. Ocular and orbital volumes were also found to be equally, and in most cases, more highly correlated with five frontal lobe gyri than with occipital lobe gyri associated with V1, V2, and V3 of the visual cortex. Additionally, after accounting for age, sex, visual acuity, and body size differences, the relationships between eye and visual cortical volumes were no longer statistically significant for all variables using Brain Parser 56 ROI, and for all except the lingual gyrus using FreeSurfer 5.3.0. The relationship between orbital and visual cortical volumes remained significant for a number of occipital lobe gyri even after accounting for these cofactors, however it was again found to be equally, and often more highly correlated with the frontal lobe gyri than with occipital lobe gyri involved in visual processing.
These results indicate that eye volume explains only a small amount of variation in orbital and visual cortical volume, and that the eye and orbit are generally more structurally associated with the frontal lobes than they are functionally associated with the visual cortex of the occipital lobes.
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