A 55-year-old man with poorly controlled hypertension and type 2 diabetes mellitus comes to the emergency department due to difficulty seeing. He has had blurry vision for the last 2 weeks, and 1 day ago he suddenly noticed a shadow develop across the visual field of his left eye. The patient has no recent headache, double vision, vertigo, light sensitivity, or nausea. On examination, pupils are equal and reactive to light. There is an area of reduced vision in the left eye. Funduscopic examination reveals a flame-shaped hemorrhage in the left temporal hemiretina. Transmission of visual information to which of the following structures is most likely impaired in this patient?
Show Explanatory Sources
Visual information from the nasal visual field of the left eye will be conveyed through the:
left temporal hemiretina (light that enters the eye forms an image on the retina that is inverted and reversed).
left optic nerve, which transmits information from one eye.
left lateral portion of the optic chiasm. Information from the temporal hemiretina does NOT cross at the optic chiasm but travels along the lateral edge of the chiasm to stay in the left side of the brain.
left optic tract. After the optic chiasm, information from the binocular right visual fields travels together in the left optic tract.
left lateral geniculate nucleus of the thalamus. Neurons from the optic tract synapse on the lateral geniculate nucleus.
optic radiations. The inferior optic radiations carry information from the superior visual field through the temporal lobe (Meyer loop), and the superior optic radiations carry information from the inferior visual field through the parietal lobe.
primary visual cortex, which is located in the occipital lobe.
(Choices A, C, E and G) The inferior colliculi and medial geniculate bodies are part of the auditory pathway.
(Choice D) The medial optic chiasm contains crossing nerve fibers that transmit visual information from the bilateral nasal hemiretinas.
(Choice F) The right lateral geniculate body receives visual information from the right temporal hemiretina and the left nasal hemiretina (ie, homonymous left visual fields).
Educational objective:
Damage to the left temporal hemiretina will disrupt the transmission of visual information along the ipsilateral optic nerve, lateral optic chiasm, optic tract, lateral geniculate body, optic radiations, and primary visual cortex.