Question at position 21 The blind spot in each eye is due to a lack of photoreceptors in the back of the eye where the __________ exits.Optic nerveOptic tractOptic chiasmRetinaClear my selection单项选择题
A
Optic nerve
B
Optic tract
C
Optic chiasm
D
Retina

Question

Question at position 21 The blind spot in each eye is due to a lack of photoreceptors in the back of the eye where the __________ exits.Optic nerveOptic tractOptic chiasmRetinaClear my selection

BlackTom AI · Accepted Answer

The blind spot arises where the optic nerve exits the eye because that exit point—the optic disc—contains no photoreceptors.

1) Relevant knowledge points and concepts
- Retina: the neural layer lining the back of the eye that contains photoreceptors (rods and cones) that detect light.  
- Optic disc (optic nerve head): the spot on the retina where all ganglion cell axons converge and leave the eye as the optic nerve. No rods or cones are present at the optic disc.  
- Optic nerve: the bundle of axons that transmits visual signals from the retina to the brain.  
- Optic chiasm and optic tract: structures in the brain (at/behind the base of the brain) that relay and partially cross visual information; they are not part of the retina and thus not locations where photoreceptors are missing.

2) Step-by-step reasoning
- Light must strike photoreceptors (rods/cones) on the retina to generate visual signals.  
- At the optic disc, fibers exit the eye to form the optic nerve; anatomical space is occupied by axons and blood vessels, not photoreceptors.  
- Because there are no photoreceptors at that small retinal region, light falling on it cannot be detected, producing the physiological blind spot in each eye.

3) Intermediate anatomical clarification
- The optic disc is on the nasal side of the retina (corresponding to the temporal visual field). The brain typically “fills in” the missing information, so we don’t perceive a hole in our vision under normal binocular viewing.

4) Why the correct answer is correct
- The blind spot specifically corresponds to the optic disc where the optic nerve exits; thus the correct phrase completing the sentence is “optic nerve.”

5) Why the other options are incorrect
- Optic tract: a central pathway in the brain after the chiasm; it does not exit the eye and is not a retinal region lacking photoreceptors.  
- Optic chiasm: the crossover point of optic nerve fibers in the brain, not an exit from the eyeball.  
- Retina: the retina as a whole contains photoreceptors; saying “retina exits” is anatomically incorrect and does not identify the specific absence-of-photoreceptors site.

6) Conclusion
The blind spot is due to a lack of photoreceptors where the optic nerve exits the eye; the correct answer is Optic nerve, matching the provided answer.

Question at position 21 The blind spot in each eye is due to a lack of photoreceptors in the back of the eye where the __________ exits.Optic nerveOptic tractOptic chiasmRetinaClear my selection单项选择题

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