What is the effect of a lesion through the optic chiasm?
A lesion involving complete optic chiasm, which disrupts the axons from the nasal field of both eyes, causes loss of vision of the right half of the right visual field and the left half of the left visual field. This visual field defect is called as bitemporal hemianopia.
What are the causes of lesion in optic chiasm?
The usual suspects are pituitary adenomas, craniopharyngiomas, and meningiomas. Pituitary tumors are the most common cause of chiasmal syndromes. Visual field defects may be one of the first signs of non-functional pituitary tumor. These are much less frequent than functional adenomas.
What condition is present when there is a damage in the optic chiasm?
If the optic nerve is damaged in the optic chiasm level, it causes bitemporal hemianopia.
What visual field crosses at the chiasm?
In the optic chiasm, the fibers of the nasal retina (i.e., the temporal visual field) of each eye cross, whereas the fibers of the temporal retina (i.e., the nasal visual field) of each eye proceed uncrossed.
What part of the visual field will be lost or compromised if the optic chiasm is damaged?
Damage at site #3: the optic chiasm would be damaged. In this case, the temporal (lateral) portions of the visual field would be lost.
Why does optic chiasm damage caused bitemporal hemianopia?
When there is compression at optic chiasm, the visual impulse from both nasal retina are affected, leading to inability to view the temporal, or peripheral, vision. This phenomenon is known as bitemporal hemianopsia.
Why does damage to the optic chiasm cause peripheral blindness?
At that point, the right optic tract carries information from the temporal fibers of the right retina and the nasal fibers from the left retina—both of which deal only with the left visual field. So damage to it causes blindness in the left visual field of both eyes and leaves the right visual field intact.
What lesion causes binasal hemianopia?
Abstract. Bitemporal hemianopia is a significant pathological hallmark of a pituitary lesion; however, binasal hemianopia is rarely reported, except for its known association with other ocular diseases rather than with brain lesions.
Where is the lesion in left homonymous hemianopsia?
Left Homonymous Hemianopia: This results from lesions to the optic tract in route towards the lateral geniculate body of the thalamus (location 3) as well as lesions right after the radiating fibers leave the lateral geniculate body (location 5). These lesions are often caused by strokes or neoplasms.
Which of these lesions will result in a homonymous hemianopia?
It is caused by lesions of the retrochiasmal visual pathways, ie, lesions of the optic tract, the lateral geniculate nucleus, the optic radiations, and the cerebral visual (occipital) cortex (figure 1) [1-4].
Why is stereopsis difficult in patients with lesions of the optic chiasm?
The difficulty with stereopsis in patients with lesions of the optic chiasm is most likely caused by the compression of the decussating optic nerve fibers resulting in the loss of an overlapping visual field at the fixation point. Stereo tests were demonstrated to be simple and effective adjunctive …
What are the symptoms of damage to the optic chiasm?
The most frequent symptoms of patients with lesions that damage the optic chiasm are progressive loss of central acuity and dimming of the visual field, particularly in its temporal portion. In addition, bitemporal field defects, whether complete or scotomatous, may produce two other types of visual symptoms.
What is the relationship between bitemporal hemianopia and chiasmal lesions?
Conversely, if a lesion of the optic chiasm that has produced a bitemporal hemianopia extends to the right optic nerve, it will eventually produce blindness or near-blindness of the right eye. Similarly, if a chiasmal lesion extends into the right optic tract, there is again blindness or near-blindness of the right eye.
What is Group 1 of optic chiasm lesion?
Group 1 consisted of 13 patients with lesions involving the optic chiasm (regardless of their visual field loss) diagnosed by magnetic resonance imaging findings.