Visual pathway lesions and the visual field defects they cause

Updated 17 September 2026

Quick answer

The pattern of a visual field defect shows where the visual pathway is damaged. A lesion in front of the optic chiasm affects one eye; a lesion of the chiasm typically causes a bitemporal hemianopia; and any lesion behind the chiasm causes a homonymous defect on the opposite side in both eyes. The further back the lesion, the more congruous — alike in the two eyes — the defect becomes, so an occipital lesion gives a congruous homonymous hemianopia, often with macular sparing.

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The pathway in brief

Retinal ganglion cell axons leave each eye in the optic nerve. At the optic chiasm, fibers from the nasal retina — which see the temporal visual field — cross to the other side, while fibers from the temporal retina stay on the same side. Each optic tract therefore carries the opposite half of the visual field from both eyes to the lateral geniculate nucleus. From there the optic radiations run to the primary visual cortex in the occipital lobe: the lower fibers loop through the temporal lobe (Meyer's loop) and carry the upper visual field, and the upper fibers pass through the parietal lobe and carry the lower visual field.

Lesion site and field defect

Lesion site	Field defect	Typical causes
Optic nerve	One eye only: central scotoma, altitudinal or arcuate defect, or complete loss; RAPD in that eye	Optic neuritis, ischemic optic neuropathy, glaucoma, compression
Junction of optic nerve and chiasm	Junctional scotoma: central scotoma in one eye plus a superotemporal defect in the other	Compressive lesions such as meningioma or pituitary tumor
Optic chiasm	Bitemporal hemianopia; pituitary tumors pressing from below usually affect the upper temporal fields first	Pituitary adenoma, craniopharyngioma, meningioma
Optic tract	Incongruous contralateral homonymous hemianopia; RAPD in the eye opposite the lesion	Stroke, tumor, trauma
Meyer's loop (temporal lobe)	Contralateral homonymous superior quadrantanopia ("pie in the sky")	Temporal lobe stroke or tumor, temporal lobectomy
Parietal optic radiations	Contralateral homonymous inferior quadrantanopia ("pie on the floor")	Parietal stroke or tumor
Occipital cortex	Congruous contralateral homonymous hemianopia, often with macular sparing	Posterior cerebral artery stroke
Occipital pole	Congruous homonymous central scotomas	Trauma, watershed infarction

Rules that help you localize

A defect that respects the vertical meridian means a lesion at or behind the chiasm. One that respects the horizontal meridian suggests optic nerve or retinal disease, such as the altitudinal defect of ischemic optic neuropathy.
Congruity increases from the optic tract (incongruous) to the occipital cortex (highly congruous).
Macular sparing points to the occipital cortex, where the macular area often has a dual blood supply from the posterior and middle cerebral arteries.
Visual acuity is usually normal with a one-sided lesion behind the chiasm, because half of each macula still works.
The temporal crescent — the far temporal field of one eye, seen by that eye alone — is represented in the most anterior occipital cortex, so it can be spared or affected on its own.

Testing the visual fields at the bedside

Sit about 1 m opposite the patient at the same eye level. The patient covers their left eye while you close your right eye, so that you compare the patient's field with your own.
Ask the patient to keep looking at your open eye.
Test each quadrant with finger counting or a moving finger held midway between you, then compare the redness of a red target across the vertical meridian.
Present targets in both halves of the field at the same time to check for visual extinction.
Confirm any defect with formal perimetry, such as automated static perimetry.

Practice it on the virtual patient

Open the visual pathway simulator.
Place a lesion on the optic nerve, chiasm, optic tract, Meyer's loop, parietal radiations and occipital cortex in turn, and watch the field chart of each eye.
Work through the lessons to review the anatomy behind each pattern.
Test yourself with the case quiz.

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Frequently asked questions

What causes a bitemporal hemianopia?

A lesion of the optic chiasm, most often a pituitary adenoma pressing from below, which usually affects the upper temporal fields first. Craniopharyngioma and meningioma are other causes.

What does "pie in the sky" mean?

"Pie in the sky" is a contralateral homonymous superior quadrantanopia caused by a lesion of Meyer's loop in the temporal lobe. A parietal lesion causes the opposite, "pie on the floor": a contralateral homonymous inferior quadrantanopia.

Why is the macula often spared in an occipital stroke?

The macular cortex at the occipital pole often receives blood from both the posterior and middle cerebral arteries, and central vision has a very large cortical representation, so a posterior cerebral artery stroke frequently spares central vision.

Where is the lesion in a right homonymous hemianopia?

Behind the optic chiasm on the left side: the left optic tract, left lateral geniculate nucleus, left optic radiations or left occipital cortex. How congruous the defect is and the associated signs help narrow it down.