A child shows declining visual ability was found to have a...

A child shows declining visual ability was found to have a swelling pressing on the optic chiasma. The tumor was found to be a craniopharyngioma. This tumor most probably occurs in the remnant of the following embryonic structure a. Diencephalon b. Septum transversum c. Rathke's pouch d. Telencephalon

Transcript

00:01 This question asks, a patient comes in with a tumor of the pituitary gland, which has grown upward into the optic chasm and caused a visual field defect.

00:10 The most likely defect from compression of the optic chasm is complete blindness in one eye, loss of the upper visual field in both eyes, loss of the nasal visual field in both eyes, or loss of the temporal visual fields in both eyes.

00:27 So here we are testing our knowledge of both the eye anatomy and also the nerve fibers that will carry the transduced electrical impulse from the optic nerve or from the retina via the optic nerve to the brain.

00:47 So the optic chasm is going to be this crossing over of the different fibers of the optic nerve.

00:57 So the fibers that will come from the nasal half of the retina from both eyes will cross in the chasm and they will join the optic tract on the opposite side.

01:11 There's a crossing over of fibers.

01:14 So the key takeaway here is going to be in the optic chasm we have a crossing over of optic nerve fibers.

01:31 Okay? if we think about each eye, we know that the lens in each of these eyes will cause inversion.

01:43 So the image on the nasal half the retina will actually originate in the temporal visual field.

01:48 So if we are referring to a tumor that will be growing and disrupting the opticism, well, if we find that we have this crossing over of the fibers coming from the nasal, portion of the retina, well, anything that we are going to receive on the nasal portion of the retina will actually originate in the temporal visual field...

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