optic chiasma
n.
A structure in the brain formed by the partial intersection or crossing of the optic nerve fibers on the underside of the hypothalamus. Also called optic chiasm.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.
optic chiasma
The junction of the two OPTIC NERVES lying under the brain. In the chiasma optic nerve fibres from the inner half of each RETINA cross over. Those from the outer half do not. Thus fibres from the inner half of each retina run out of the chiasma in close association with fibres from the outer half of the retina on the other side. The two optic tracts so formed run into the brain. This arrangement ensures that input to both eyes from the right field of vision causes signals that pass to the left half of the brain, and vice versa.Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005
optic chiasma
a point under the hypothalamus of the brain where the two optic nerves meet and cross over, so that stimuli from each eye are interpreted in the OPTIC LOBE of the opposite side of the brain.Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005
chiasma, optic
A structure located above the pituitary gland and formed by the junction and partial decussation (crossing-over) of the optic nerves. The fibres from the nasal half of the retina of the left eye cross over to join the fibres from the temporal half of the right retina to make up the right optic tract and vice versa. About 53% of the axons of the optic nerves cross to the opposite tract (Fig. C9). A lesion of the chiasma produces a typical field defect (heteronymous hemianopia). Note: also spelt chiasm. See circle of Willis; decussation; visual pathway; stereo-blindness; optic tracts.
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Fig. C9 An illustration of the decussation of the optic nerve fibres occurring in the optic chiasma
Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann