Neurophysiology and special senses: visual field defect: practice question

A Physiology 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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Physiology · Neurophysiology and special senses: visual field defect

Sample item

A patient with a pituitary adenoma has progressive loss of the outer halves of both visual fields. Which fibres are compressed?

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

The answer and the reasoning

C. Crossing fibres from the nasal halves of both retinae

Fibres from the nasal retina, which see the temporal visual field, cross in the optic chiasm. A pituitary tumour presses on the chiasm from below, damaging these fibres first and causing bitemporal hemianopia. Optic tract lesions cause a homonymous defect.

Option by option

  • A. Fibres of the optic radiation in the temporal lobe

    Temporal lobe radiation lesions cause a superior homonymous quadrantanopia.

  • B. Fibres of the right optic tract

    An optic tract lesion causes a contralateral homonymous hemianopia.

  • C. Crossing fibres from the nasal halves of both retinae (correct)

    Correct. Compression of crossing nasal fibres gives bitemporal hemianopia.

  • D. Uncrossed fibres from the temporal halves of both retinae

    Uncrossed temporal fibres would give loss of the nasal fields.

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.

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Questions about this Physiology question

What is the answer to this Physiology question?

The best answer is C, Crossing fibres from the nasal halves of both retinae. Fibres from the nasal retina, which see the temporal visual field, cross in the optic chiasm.

Why is "Fibres of the optic radiation in the temporal lobe" not the answer?

Temporal lobe radiation lesions cause a superior homonymous quadrantanopia.

Why is "Fibres of the right optic tract" not the answer?

An optic tract lesion causes a contralateral homonymous hemianopia.

Why is "Uncrossed fibres from the temporal halves of both retinae" not the answer?

Uncrossed temporal fibres would give loss of the nasal fields.

What concept does this question test?

It tests Neurophysiology and special senses: visual field defect in Physiology. A pituitary tumour presses on the chiasm from below, damaging these fibres first and causing bitemporal hemianopia. Optic tract lesions cause a homonymous defect.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. 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 Neurophysiology and special senses: visual field defect?

For each system, sketch the key graph (pressure–volume loop, oxygen dissociation curve, nephron handling) and explain it aloud. Then use the flashcards and the other Physiology 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.