optic chiasma n the X-shaped partial decussation on the undersurface of the hypothalamus through which the optic nerves are continuous with the brain called also optic chiasm
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the X-shaped structure formed by the two optic nerves, which pass backwards from the eyeballs to meet in the midline beneath the brain, near the pituitary gland. Nerve fibres from the nasal side of the retina of each eye cross over to join fibres from the lateral side of the retina of the opposite eye. The optic tracts resulting from the junction pass backwards to the occipital lobes.
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chiasma opticum [TA] optic chiasm: the part of the hypothalamus formed by the decussation, or crossing, of the fibers of the optic nerve from the medial half of each retina; called also optic decussation.
Medical dictionary. 2011.