the optic nerve sends most of its information to primary visual cortex.
the optic nerve sends most of its information to primary visual cortex.
where does the optic nerve send most of its information?
primary visual cortex
the optic nerve can be damaged when exposed to direct or indirect injury. direct optic nerve injuries are caused by trauma to the head or orbit that crosses normal tissue planes and disrupts the anatomy and function of the optic nerve; e.g., a bullet or forceps that physically injures the optic nerve. indirect injuries, like blunt trauma to the forehead during a motor vehicle accident, transmit force to the optic nerve without transgressing tissue planes. this type of force causes the optic nerve to absorb excess energy at the time of impact. the most common site of injury of the optic nerve is the intracanalicular portion of the nerve. deceleration injuries from motor vehicle or bicycle accidents account for 17 to 63 percent of cases. falls are also a common cause, and optic neuropathy most commonly occurs when there is a loss of consciousness associated with multi-system trauma and serious brain injury. in less than three percent of patients, an orbital hemorrhage after an injection behind the eye (retrobulbar block) can cause injury to the optic nerve, but this is readily manageable if it does not involve direct optic nerve injury and is caught early. the role of high-dose steroids and orbital decompression in treating these patients is controversial and, if administered, must be done very soon after injury with minimal effects. in patients with an orbital fracture, vomiting or nose blowing can force air into the orbit and possibly compromise the integrity of the optic nerve.
optic neuropathy
the crossing of the nasal half of macular fibers of central vision occurs posteriorly in the chiasm. the inferior and superior fibers remain inferior or superior, respectively. however, the inferonasal fibers pass more anteriorly in the chiasm while the superonasal fibers pass more posteriorly. classical teaching was that, once crossed, the inferonasal fibers briefly loop back into the contralateral optic nerve sheath, before returning to the chiasm. this bend into the contralateral optic nerve had been called wilbrand's knee. however, today there is significant evidence that wilbrand’s knee is simply an artifact (error). optic nerve axons from one eye can only be selectively studied in the human after enucleation of the contralateral eye and thus degeneration of the axons on one side. after several years, the occurring optic nerve atrophy results in artifactual looping of the axons into the atrophic nerve. this looping was initially described by wilbrand, who studied subjects with severe optic nerve atrophy after enucleation, and who then appears to have exaggerated the importance of this looping in later drawings. clinically, no optic field deficits have been observed in a small series of optic nerve sections at the optic nerve-chiasm junction.
chiasmal syndrome