Which one of the following would be true if only the left optic nerve was severed?
**Core Concept**
The optic nerves transmit visual information from the retina to the brain, allowing us to perceive and interpret visual stimuli. The visual pathway is bilateral, meaning that each eye has a contralateral connection to the brain, primarily through the optic chiasm. Damage to one optic nerve primarily affects the ipsilateral eye.
**Why the Correct Answer is Right**
When the left optic nerve is severed, the most significant consequence is the loss of vision in the left eye (ipsilateral). This is because the left optic nerve is responsible for transmitting visual information from the left eye to the brain. The contralateral eye (right eye) will still be able to transmit visual information through the intact right optic nerve. The visual field defects resulting from optic nerve damage can be assessed using a visual field test, which can help identify the affected area.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because severing only the left optic nerve would not cause a complete loss of vision in both eyes. The right eye would still be able to transmit visual information through its intact optic nerve.
**Option B:** This option is incorrect because it is not a direct consequence of severing the left optic nerve. While the patient may experience some visual disturbances, it is not the most accurate description of the primary effect.
**Option C:** This option is incorrect because it is not a direct consequence of severing the left optic nerve. The visual field defect would be limited to the left eye's visual field, not both eyes.
**Option D:** This option is incorrect because it is not a direct consequence of severing the left optic nerve. The patient may experience some visual disturbances, but it is not the most accurate description of the primary effect.
**Clinical Pearl / High-Yield Fact**
In cases of optic nerve damage, a visual field test can help identify the affected area and guide further management. It is essential to assess the patient's visual acuity, visual field, and pupillary reactions to determine the extent of the damage.
**Correct Answer: C. The patient would have a left homonymous hemianopia.**