Neuro-ophthalmology and pupils: macular sparing: practice question

A Ophthalmology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Ophthalmology · Neuro-ophthalmology and pupils: macular sparing

Sample item

A patient with a right posterior cerebral artery stroke has a left homonymous hemianopia, but the central 5 degrees of the visual field is preserved. What best explains the preserved central vision?

AThe macula does not project to the cortexBThe macula is represented in the lateral geniculate body onlyCOccipital pole also receives blood from the middle cerebral arteryDMacular fibres cross entirely at the chiasm

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

C. Occipital pole also receives blood from the middle cerebral artery

The occipital pole, which represents the macula, has a dual blood supply from the posterior and middle cerebral arteries, so it survives a posterior cerebral occlusion. This produces a homonymous hemianopia with macular sparing. Macular fibres project bilaterally to the cortex.

Option by option

A. The macula does not project to the cortex
The macula projects to a large area of cortex at the occipital pole.
B. The macula is represented in the lateral geniculate body only
The macula is represented at the geniculate and then the cortex, so this does not explain sparing.
C. Occipital pole also receives blood from the middle cerebral artery (correct)
Correct. The dual supply keeps the macular cortex alive in posterior cerebral occlusion.
D. Macular fibres cross entirely at the chiasm
Macular fibres partly cross and partly stay uncrossed, so they reach both hemispheres.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

Questions about this Ophthalmology question

What is the answer to this Ophthalmology question?

The best answer is C, Occipital pole also receives blood from the middle cerebral artery. The occipital pole, which represents the macula, has a dual blood supply from the posterior and middle cerebral arteries, so it survives a posterior cerebral occlusion.

Why is "The macula does not project to the cortex" not the answer?

The macula projects to a large area of cortex at the occipital pole.

Why is "The macula is represented in the lateral geniculate body only" not the answer?

The macula is represented at the geniculate and then the cortex, so this does not explain sparing.

Why is "Macular fibres cross entirely at the chiasm" not the answer?

Macular fibres partly cross and partly stay uncrossed, so they reach both hemispheres.

What concept does this question test?

It tests Neuro-ophthalmology and pupils: macular sparing in Ophthalmology. This produces a homonymous hemianopia with macular sparing. Macular fibres project bilaterally to the cortex.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Neuro-ophthalmology and pupils: macular sparing?

Group the red eye by what to examine and what the pupil does. Then use the flashcards and the other Ophthalmology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.