If a patient suffers visual impairment only in one eye, why must the damage be located in the visual pathway prior to the optic chiasma?

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Hi, everyone. Let's take a look at this practice problem together. A lesion was compressing the optic chiasm of a patient. What kind of blindness would you expect to see in this patient? The answer options are a scat toma B, homonymous hemianopsia, C bi temporal hemianopsia and d complete blindness. So a fair warning. This question is long. The optic chiasm can be a complicated subject. So pause and review concepts if you need to recall that the optic chiasm is the area of the brain where optic nerves from each eye cross each other. Why this anatomy allows us to have binocular vision on the screen? I am putting up a drawing of the optic chiasm. I will circle things on this drawing that I'm referencing as I talk. Now the circles are the eyeballs and recall that each eye has a nasal side and a temporal side of the retina and they are drawn in different colors for each eye. Let's talk about each eye individually. In the left eye, the temporal retina in blue receives visual information from the left nasal visual field. Also in blue nerve fibers carry that information to the same side of the brain as the eye. So to the left hemisphere of the brain, the nasal retina of the left eye in orange receives information from the left temporal visual field in orange. And this is carried in nerve fibers that will cross at the optic chiasm and relay that information to the right hemisphere of the brain. Now, in the right eye, the temporal retina in orange receives information from the right nasal visual field which is also an orange and this information is carried to the same side of the brain as the eye. So to that right hemisphere, now the nasal retina of the right eye which is drawn in blue, receives information from the right temporal visual field in blue and that is carried along nerve fibers that cross at the cop optic chiasm and carried to the left hemisphere of the brain. So note that at the optic chiasm which I am circling in red. Now it's the nerve fibers from the nasal side of each eye that cross over. Now, what I just went through is just a short summary. So again, please re-watch that that explanation or look up anything you need to. It is a tricky concept to understand initially. Now, back to the question, there is a lesion that is compressing the optic chiasm and thus it is compressing the nerve fibers that are crossing at this point. Now, what nerve fibers were those? Well, it's the nerve fibers from the nasal retina of both eyes and I will circle those in red. Now they are receiving information from the temporal visual fields. Thus, the information received from the temporal visual fields are going to be affected. So which of the answer options is the term that describes this? Well, option A Koma recall that this is a blind spot or a term for an area of partial loss of vision. So option A is incorrect. Option B, homonymous hemianopsia. This is the term for vision loss on the same side in both eyes. So for example, you lose complete vision on the left side or you lose complete vision on the right side. So option B is also incorrect and option D is as well, complete blindness is complete vision loss. So the correct option is the bi temporal hemianopsia. This is the loss of the temporal visual fields from each side or you can say your peripheral vision. So again, it's the fibers that cross at the optic chiasm that come from the nasal retina of each eye and receive information from the temporal visual fields that is going to be affected by that lesion. So the correct answer is option C bi temporal hemianopsia. All right, everyone. I hope you found this helpful and I'll see you soon for the next practice problem.

If a patient suffers visual impairment only in one eye, why must the damage be located in the visual pathway prior to the optic chiasma?

Verified Solution

Key Concepts

Visual Pathway

Optic Chiasm

Unilateral Visual Impairment