Bitemporal Hemianopia: Chiasm Clues

Master bitemporal hemianopia localization, classic chiasmal causes and visual-field patterns for NBEO and OKAP preparation.

Reviewed for accuracyJuly 27, 20262 min read

Warm-up

Which of the following is the most common cause of bitemporal hemianopia in adults?

Lesson

Bitemporal Hemianopia in 30 Seconds

Bitemporal hemianopia localizes to the optic chiasm. It results from damage to crossing nasal retinal ganglion cell axons, which carry temporal visual-field information from each eye. The defect respects the vertical midline and typically spares the nasal fields.

Why the Chiasm Is the Localizer

Bitemporal hemianopia results from a lesion at the optic chiasm itself because crossing nasal retinal fibers carry the temporal visual field of each eye and decussate there. Homonymous hemianopia indicates a retrochiasmal lesion and affects the same side of visual space in both eyes. A junctional scotoma indicates an anterior chiasmal lesion involving one optic nerve and adjacent crossing chiasmal fibers.

Classic Causes and Patterns

Pituitary adenomas often compress the inferior aspect of the chiasm from below and classically produce superior temporal field loss first, although the pattern varies with chiasmal anatomy and tumor growth.
Craniopharyngiomas often compress the superior aspect of the chiasm and may preferentially produce inferior temporal field loss.
A junctional scotoma suggests anterior chiasmal involvement: ipsilateral optic neuropathy with a superior temporal field defect in the fellow eye.
Other compressive causes include meningioma and aneurysm. Early chiasmal compression often produces asymmetric or incomplete temporal defects before a complete bitemporal hemianopia develops.

4 Facts Exams Always Ask

A superior temporal defect favors pituitary compression from below. An inferior temporal defect favors craniopharyngioma compression from above, although the pattern is not universal.
Bitemporal hemianopia respects the vertical midline because the chiasm separates fibers by visual hemifield, like retrochiasmal homonymous defects.
Patients may report bumping into objects, difficulty driving or changing lanes, and trouble seeing people approaching from the side.
Sellar and suprasellar lesions causing chiasmal compression may also affect pituitary function, producing endocrine abnormalities.

The Classic Trap

Do not label every bilateral field defect as bitemporal hemianopia. Confirm that the loss respects the vertical midline and that nasal fields are spared. Also look for a junctional scotoma. An ipsilateral optic-nerve defect with a fellow-eye temporal defect localizes to the optic nerve and anterior chiasm, not the chiasm alone.

Clinical Pearl

Peripheral field loss often precedes loss of central visual acuity, making automated perimetry essential when chiasmal compression is suspected. A vertical-meridian-respecting temporal field defect can signal a clinically important chiasmal lesion even with normal acuity.

Check yourself

Checkpoint 1

Which visual field defect is most characteristic of a compressive lesion at the optic chiasm?

Checkpoint 2

A junctional scotoma of Traquair, consisting of a central scotoma in one eye and a superotemporal defect in the fellow eye, localizes a lesion to which specific site?

Explanation

A junctional scotoma occurs when a lesion affects the optic nerve at its junction with the chiasm, damaging ipsilateral nerve fibers (causing a central scotoma) as well as crossing fibers from the contralateral inferonasal retina that loop anteriorly into the optic nerve (Wilbrand's knee) before decussating, producing a contralateral superotemporal field defect. This precise localization is a classic board exam concept, though the anatomic existence of Wilbrand's knee has been debated in more recent literature.

Clinical case

A 42-year-old patient reports frequently striking objects on either side while walking. Visual acuity is 20/20 in both eyes. Automated perimetry shows symmetric loss in the superior temporal field of each eye, sharply respecting the vertical midline. The patient also reports reduced libido and fatigue. Fundus examination is normal.

A patient presents with bitemporal hemianopia that is denser superiorly than inferiorly. Where is the compressive lesion most likely located relative to the chiasm?

Explanation

Superior bitemporal field loss occurs when a lesion compresses the chiasm from above and behind, such as a craniopharyngioma, because the inferior crossing fibers (serving the superior temporal field) are affected preferentially. In contrast, inferior pituitary tumors compressing from below typically produce a denser inferior bitemporal defect.

Case discussion

The symmetric superior bitemporal defect localizes to the optic chiasm. Its superior predominance suggests compression from below and anterior to the chiasm, classically from a pituitary macroadenoma. The endocrine symptoms support a sellar process near the pituitary gland. A normal fundus is expected early in compression, before chronic optic nerve involvement leads to atrophy.

Sources & Reviewer Info

Reviewed by Vasilis Inglezis: Optometrist and Ocular Oncology Imaging Specialist, Ocular Oncology Center, Athens, Greece. Last updated July 27, 2026.

References

American Academy of Ophthalmology. Basic and Clinical Science Course, Section 5: Neuro-Ophthalmology.
Miller NR, Newman NJ, Biousse V, Kerrison JB. Walsh and Hoyt's Clinical Neuro-Ophthalmology.
Bowling B. Kanski's Clinical Ophthalmology.

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