Medicine – Visual Field Defects and Lesion Localisation

Visual field defects are important neurological and ophthalmological signs because the pattern of visual loss can help localise a lesion along the visual pathway. A useful first distinction is whether the abnormality affects one eye only or corresponding visual fields of both eyes.

In general:

One-eye defects → think retina or optic nerve.

Both-eye field defects → think optic chiasm or structures behind the chiasm.

1. Visual Pathway

Visual information begins in the retina and travels through the:

Retina → optic nerve → optic chiasm → optic tract → lateral geniculate nucleus → optic radiations → primary visual cortex in the occipital lobe.

At the optic chiasm, fibres arising from the nasal retina cross to the opposite side, whereas fibres from the temporal retina remain uncrossed.

This crossing explains the characteristic visual-field defects produced by lesions at different levels.

2. Lesions Affecting One Eye

Visual loss confined to one eye usually indicates pathology anterior to the optic chiasm.

Possible sites include:

Eye itself.

Retina.

Optic nerve.

The precise visual-field abnormality depends on which structure is affected.

3. Complete Monocular Visual Loss

Complete loss of vision in one eye can occur with severe damage to the ipsilateral optic nerve.

A complete optic nerve transection therefore causes:

Complete blindness of the affected eye.

For example:

Right optic nerve transection → complete right monocular blindness.

The opposite eye remains unaffected if the lesion is confined to the right optic nerve.

4. Other Causes of Severe Monocular Visual Loss

Although optic nerve transection is the classic anatomical example, complete or profound monocular visual loss can also result from severe ocular, retinal, or optic nerve disease.

Important possibilities include:

Central retinal artery occlusion.

Severe optic neuropathy.

Retinal detachment involving the macula.

Major ocular trauma.

Therefore, monocular blindness does not automatically mean that the optic nerve has literally been transected.

5. Central Scotoma

A scotoma is a localized area of reduced or absent vision surrounded by relatively preserved vision.

A central scotoma affects the central part of the visual field and may be experienced as a blurred, dark, or missing area directly in front of the patient.

Central scotomas are particularly associated with diseases affecting the optic nerve or macula.

6. Optic Neuritis

Optic neuritis is an important cause of a central or centrocaecal scotoma.

Typical features include:

Reduced visual acuity.

Central visual-field loss.

Reduced colour vision, particularly red desaturation.

Pain on eye movement.

Relative afferent pupillary defect when unilateral or asymmetric.

Optic neuritis is particularly associated with demyelinating disorders such as multiple sclerosis.

7. Constricted Visual Field

A constricted visual field means that the peripheral visual field progressively narrows while central vision may initially remain relatively preserved.

This may eventually produce tunnel vision.

Important causes include:

Chronic glaucoma.

Chronic papilloedema with secondary optic nerve damage.

Another important cause of progressive peripheral field constriction is retinitis pigmentosa.

8. Chronic Glaucoma

In chronic glaucoma, progressive optic nerve damage produces characteristic visual-field abnormalities.

Early defects may include:

Paracentral scotomas.

Nasal steps.

Arcuate scotomas.

As disease becomes advanced, the remaining visual field may become markedly constricted, producing:

Tunnel vision.

Therefore:

Advanced chronic glaucoma → severe peripheral field constriction.

9. Chronic Papilloedema

Long-standing papilloedema from raised intracranial pressure can eventually damage optic nerve axons.

Early papilloedema often causes an enlarged blind spot, while visual acuity may initially remain relatively preserved.

If papilloedema persists:

Chronic disc swelling → optic nerve damage → secondary optic atrophy → progressive visual-field loss.

Advanced disease can therefore produce substantial field constriction and permanent visual impairment.

10. Lesions Affecting Both Eyes

When a lesion affects corresponding parts of the visual fields of both eyes, pathology at the optic chiasm or behind the chiasm should be considered.

Important sites include:

Optic chiasm.

Optic tract.

Lateral geniculate nucleus.

Optic radiations.

Occipital visual cortex.

The exact field defect helps localise the lesion.

11. Bitemporal Hemianopia

Bitemporal hemianopia means loss of the temporal half of the visual field in both eyes.

This pattern strongly suggests a lesion involving the optic chiasm.

Therefore:

Bitemporal hemianopia → think optic chiasm.

12. Why Chiasmal Lesions Cause Bitemporal Hemianopia

The nasal retinal fibres cross at the optic chiasm.

These nasal retinal fibres carry information from the temporal visual fields.

Compression of the central optic chiasm therefore preferentially damages the crossing nasal fibres.

The result is:

Loss of temporal visual field in both eyes → bitemporal hemianopia.

13. Causes of Chiasmal Lesions

Important causes include:

Pituitary adenoma.

Craniopharyngioma.

Meningioma.

Intracranial aneurysm, depending on its location.

Other suprasellar masses may also compress the optic chiasm.

14. Pituitary Adenoma

A pituitary adenoma is a classic cause of bitemporal hemianopia.

The pituitary gland lies beneath the optic chiasm.

As a pituitary tumour expands upward from the sella turcica, it may compress the inferior aspect of the optic chiasm.

Therefore:

Pituitary mass → optic chiasm compression → bitemporal visual-field loss.

Endocrine abnormalities may coexist depending on whether the tumour secretes hormones or interferes with normal pituitary function.

15. Craniopharyngioma

Craniopharyngiomas are tumours arising in the sellar or suprasellar region.

Because of their proximity to the optic chiasm, they can cause:

Visual-field defects.

Reduced visual acuity.

Endocrine abnormalities.

Symptoms of raised intracranial pressure, particularly with larger lesions.

Bitemporal hemianopia may occur from chiasmal compression.

16. Homonymous Visual-Field Defects

A homonymous visual-field defect affects the same side of the visual field in both eyes.

For example:

Right homonymous hemianopia → loss of the right visual field of both eyes.

This indicates a lesion behind the optic chiasm on the opposite side.

Therefore:

Right homonymous field loss → left retrochiasmal lesion.

Left homonymous field loss → right retrochiasmal lesion.

17. Homonymous Quadrantanopia

A homonymous quadrantanopia means loss of the same quarter of the visual field in both eyes.

This commonly results from a lesion involving part of the optic radiations.

The two important patterns are:

Superior quadrantanopia → temporal lobe lesion.

Inferior quadrantanopia → parietal lobe lesion.

18. Superior Homonymous Quadrantanopia

Fibres carrying information from the superior visual field travel through the inferior optic radiations, which loop anteriorly through the temporal lobe.

This loop is known as Meyer’s loop.

A temporal lobe lesion therefore produces a contralateral superior homonymous quadrantanopia.

A useful memory phrase is:

Temporal lesion → “pie in the sky.”

For example:

Left temporal lobe lesion → right superior homonymous quadrantanopia.

19. Inferior Homonymous Quadrantanopia

Fibres carrying the inferior visual field travel more superiorly through the parietal lobe.

A parietal optic-radiation lesion therefore causes:

Contralateral inferior homonymous quadrantanopia.

A useful memory phrase is:

Parietal lesion → “pie on the floor.”

For example:

Left parietal lesion → right inferior homonymous quadrantanopia.

20. Homonymous Hemianopia

Homonymous hemianopia means loss of the same half of the visual field in both eyes.

It results from a retrochiasmal lesion.

Possible sites include:

Optic tract.

Lateral geniculate nucleus.

Optic radiations.

Occipital cortex.

21. Optic Tract Lesion

An optic tract lesion produces a contralateral homonymous hemianopia.

The defect is often relatively incongruous, meaning that the field defects in the two eyes are not exactly identical in shape or extent.

For example:

Left optic tract lesion → right homonymous hemianopia.

22. Congruity and Lesion Location

As lesions occur farther posteriorly along the visual pathway, homonymous field defects generally become more congruous.

Congruous means that the field defects in the two eyes closely resemble each other.

Therefore, as a general rule:

Anterior retrochiasmal lesion → more incongruous.

Posterior retrochiasmal lesion → more congruous.

This is a useful localisation principle rather than an absolute rule.

23. Lateral Geniculate Lesions

The lateral geniculate nucleus/body is a relay station between the optic tract and optic radiations.

Lesions here can cause a contralateral homonymous visual-field defect, sometimes with characteristic sectoral patterns depending on vascular anatomy.

The original note associates a congruous homonymous hemianopia with a lateral geniculate lesion, but congruity alone does not precisely localise the lesion.

24. Occipital Cortex Lesions

The final part of the visual pathway is the primary visual cortex in the occipital lobe.

An occipital cortex lesion typically causes a highly congruous contralateral homonymous hemianopia.

One particularly important feature is:

Macular sparing.

25. Macular Sparing

Macular sparing means that central vision is preserved despite loss of the surrounding homonymous visual field.

This is classically associated with an occipital cortex lesion, particularly an occipital infarction.

One explanation is that the occipital pole representing central vision may have overlapping vascular supply, although the mechanism is more complex than a simple fixed dual blood supply in every patient.

Therefore:

Homonymous hemianopia + macular sparing → strongly suggests occipital cortex involvement.

26. Visual Field Defects – Note Form

Complete monocular visual loss: severe ipsilateral retinal or optic nerve lesion; complete optic nerve transection is the classic anatomical example.

Central scotoma: optic nerve or macular disease; optic neuritis is an important cause.

Constricted visual field: chronic glaucoma, chronic papilloedema with optic nerve damage, or retinitis pigmentosa.

Bitemporal hemianopia: optic chiasm lesion.

Chiasmal causes: pituitary adenoma, craniopharyngioma, meningioma and other suprasellar masses; some aneurysms may also compress the chiasm.

Superior homonymous quadrantanopia: contralateral temporal lobe/Meyer’s loop lesion.

Inferior homonymous quadrantanopia: contralateral parietal optic-radiation lesion.

Homonymous hemianopia: contralateral lesion behind the optic chiasm.

Incongruous homonymous hemianopia: suggests a relatively anterior retrochiasmal lesion, such as the optic tract.

Increasingly congruous field defects: generally suggest progressively more posterior lesions.

Homonymous hemianopia with macular sparing: classically suggests an occipital cortex lesion.

27. Easy Localisation Sequence

Think of the visual pathway from front to back:

One eye only → retina or optic nerve.

Temporal fields of both eyes lost → optic chiasm.

Same side of visual field lost in both eyes → opposite retrochiasmal pathway.

Superior quadrant lost → opposite temporal lobe.

Inferior quadrant lost → opposite parietal lobe.

Very congruous homonymous hemianopia ± macular sparing → opposite occipital cortex.

Key Clinical Pattern

The most useful rule is:

PRE-CHIASM → ONE EYE.

CHIASM → BITEMPORAL HEMIANOPIA.

POST-CHIASM → CONTRALATERAL HOMONYMOUS FIELD LOSS.

For the optic radiations:

Temporal lobe → superior quadrantanopia → “pie in the sky.”

Parietal lobe → inferior quadrantanopia → “pie on the floor.”

And finally:

Occipital cortex → highly congruous homonymous hemianopia, often with macular sparing.

1. Visual Pathway Visual information begins in the retina and travels through the: Retina → optic nerve → optic chiasm → optic tract → lateral geniculate nucleus → optic radiations → primary visual cortex in the occipital lobe. At the optic chiasm, fibres arising from the nasal retina cross to the opposite side, whereas fibres from the temporal retina remain uncrossed. This crossing explains the characteristic visual-field defects produced by lesions at different levels. 

2. Lesions Affecting One Eye Visual loss confined to one eye usually indicates pathology anterior to the optic chiasm. Possible sites include: Eye itself. Retina. Optic nerve. The precise visual-field abnormality depends on which structure is affected. 

3. Complete Monocular Visual Loss Complete loss of vision in one eye can occur with severe damage to the ipsilateral optic nerve. A complete optic nerve transection therefore causes: Complete blindness of the affected eye. For example: Right optic nerve transection → complete right monocular blindness. The opposite eye remains unaffected if the lesion is confined to the right optic nerve. 

4. Other Causes of Severe Monocular Visual Loss Although optic nerve transection is the classic anatomical example, complete or profound monocular visual loss can also result from severe ocular, retinal, or optic nerve disease. Important possibilities include: Central retinal artery occlusion. Severe optic neuropathy. Retinal detachment involving the macula. Major ocular trauma. Therefore, monocular blindness does not automatically mean that the optic nerve has literally been transected. 

5. Central Scotoma A scotoma is a localized area of reduced or absent vision surrounded by relatively preserved vision. A central scotoma affects the central part of the visual field and may be experienced as a blurred, dark, or missing area directly in front of the patient. Central scotomas are particularly associated with diseases affecting the optic nerve or macula. 

6. Optic Neuritis Optic neuritis is an important cause of a central or centrocaecal scotoma. Typical features include: Reduced visual acuity. Central visual-field loss. Reduced colour vision, particularly red desaturation. Pain on eye movement. Relative afferent pupillary defect when unilateral or asymmetric. Optic neuritis is particularly associated with demyelinating disorders such as multiple sclerosis. 

7. Constricted Visual Field A constricted visual field means that the peripheral visual field progressively narrows while central vision may initially remain relatively preserved. This may eventually produce tunnel vision. Important causes include: Chronic glaucoma. Chronic papilloedema with secondary optic nerve damage. Another important cause of progressive peripheral field constriction is retinitis pigmentosa. 

8. Chronic Glaucoma In chronic glaucoma, progressive optic nerve damage produces characteristic visual-field abnormalities. Early defects may include: Paracentral scotomas. Nasal steps. Arcuate scotomas. As disease becomes advanced, the remaining visual field may become markedly constricted, producing: Tunnel vision. Therefore: Advanced chronic glaucoma → severe peripheral field constriction. 

9. Chronic Papilloedema Long-standing papilloedema from raised intracranial pressure can eventually damage optic nerve axons. Early papilloedema often causes an enlarged blind spot, while visual acuity may initially remain relatively preserved. If papilloedema persists: Chronic disc swelling → optic nerve damage → secondary optic atrophy → progressive visual-field loss. Advanced disease can therefore produce substantial field constriction and permanent visual impairment. 

10. Lesions Affecting Both Eyes When a lesion affects corresponding parts of the visual fields of both eyes, pathology at the optic chiasm or behind the chiasm should be considered. Important sites include: Optic chiasm. Optic tract. Lateral geniculate nucleus. Optic radiations. Occipital visual cortex. The exact field defect helps localise the lesion. 

11. Bitemporal Hemianopia Bitemporal hemianopia means loss of the temporal half of the visual field in both eyes. This pattern strongly suggests a lesion involving the optic chiasm. Therefore: Bitemporal hemianopia → think optic chiasm. 

12. Why Chiasmal Lesions Cause Bitemporal Hemianopia The nasal retinal fibres cross at the optic chiasm. These nasal retinal fibres carry information from the temporal visual fields. Compression of the central optic chiasm therefore preferentially damages the crossing nasal fibres. The result is: Loss of temporal visual field in both eyes → bitemporal hemianopia. 

13. Causes of Chiasmal Lesions Important causes include: Pituitary adenoma. Craniopharyngioma. Meningioma. Intracranial aneurysm, depending on its location. Other suprasellar masses may also compress the optic chiasm. 

14. Pituitary Adenoma A pituitary adenoma is a classic cause of bitemporal hemianopia. The pituitary gland lies beneath the optic chiasm. As a pituitary tumour expands upward from the sella turcica, it may compress the inferior aspect of the optic chiasm. Therefore: Pituitary mass → optic chiasm compression → bitemporal visual-field loss. Endocrine abnormalities may coexist depending on whether the tumour secretes hormones or interferes with normal pituitary function. 

15. Craniopharyngioma Craniopharyngiomas are tumours arising in the sellar or suprasellar region. Because of their proximity to the optic chiasm, they can cause: Visual-field defects. Reduced visual acuity. Endocrine abnormalities. Symptoms of raised intracranial pressure, particularly with larger lesions. Bitemporal hemianopia may occur from chiasmal compression. 

16. Homonymous Visual-Field Defects A homonymous visual-field defect affects the same side of the visual field in both eyes. For example: Right homonymous hemianopia → loss of the right visual field of both eyes. This indicates a lesion behind the optic chiasm on the opposite side. Therefore: Right homonymous field loss → left retrochiasmal lesion. Left homonymous field loss → right retrochiasmal lesion. 

17. Homonymous Quadrantanopia A homonymous quadrantanopia means loss of the same quarter of the visual field in both eyes. This commonly results from a lesion involving part of the optic radiations. The two important patterns are: Superior quadrantanopia → temporal lobe lesion. Inferior quadrantanopia → parietal lobe lesion. 

18. Superior Homonymous Quadrantanopia Fibres carrying information from the superior visual field travel through the inferior optic radiations, which loop anteriorly through the temporal lobe. This loop is known as Meyer’s loop. A temporal lobe lesion therefore produces a contralateral superior homonymous quadrantanopia. A useful memory phrase is: Temporal lesion → “pie in the sky.” For example: Left temporal lobe lesion → right superior homonymous quadrantanopia. 

19. Inferior Homonymous Quadrantanopia Fibres carrying the inferior visual field travel more superiorly through the parietal lobe. A parietal optic-radiation lesion therefore causes: Contralateral inferior homonymous quadrantanopia. A useful memory phrase is: Parietal lesion → “pie on the floor.” For example: Left parietal lesion → right inferior homonymous quadrantanopia. 

20. Homonymous Hemianopia Homonymous hemianopia means loss of the same half of the visual field in both eyes. It results from a retrochiasmal lesion. Possible sites include: Optic tract. Lateral geniculate nucleus. Optic radiations. Occipital cortex. 

21. Optic Tract Lesion An optic tract lesion produces a contralateral homonymous hemianopia. The defect is often relatively incongruous, meaning that the field defects in the two eyes are not exactly identical in shape or extent. For example: Left optic tract lesion → right homonymous hemianopia. 

22. Congruity and Lesion Location As lesions occur farther posteriorly along the visual pathway, homonymous field defects generally become more congruous. Congruous means that the field defects in the two eyes closely resemble each other. Therefore, as a general rule: Anterior retrochiasmal lesion → more incongruous. Posterior retrochiasmal lesion → more congruous. This is a useful localisation principle rather than an absolute rule. 

23. Lateral Geniculate Lesions The lateral geniculate nucleus/body is a relay station between the optic tract and optic radiations. Lesions here can cause a contralateral homonymous visual-field defect, sometimes with characteristic sectoral patterns depending on vascular anatomy. The original note associates a congruous homonymous hemianopia with a lateral geniculate lesion, but congruity alone does not precisely localise the lesion. 

24. Occipital Cortex Lesions The final part of the visual pathway is the primary visual cortex in the occipital lobe. An occipital cortex lesion typically causes a highly congruous contralateral homonymous hemianopia. One particularly important feature is: Macular sparing. 

25. Macular Sparing Macular sparing means that central vision is preserved despite loss of the surrounding homonymous visual field. This is classically associated with an occipital cortex lesion, particularly an occipital infarction. One explanation is that the occipital pole representing central vision may have overlapping vascular supply, although the mechanism is more complex than a simple fixed dual blood supply in every patient. Therefore: Homonymous hemianopia + macular sparing → strongly suggests occipital cortex involvement. 

26. Visual Field Defects – Note Form Complete monocular visual loss: severe ipsilateral retinal or optic nerve lesion; complete optic nerve transection is the classic anatomical example. 

Central scotoma: optic nerve or macular disease; optic neuritis is an important cause. 

Constricted visual field: chronic glaucoma, chronic papilloedema with optic nerve damage, or retinitis pigmentosa. 

Bitemporal hemianopia: optic chiasm lesion. 

Chiasmal causes: pituitary adenoma, craniopharyngioma, meningioma and other suprasellar masses; some aneurysms may also compress the chiasm. 

Superior homonymous quadrantanopia: contralateral temporal lobe/Meyer’s loop lesion. 

Inferior homonymous quadrantanopia: contralateral parietal optic-radiation lesion. 

Homonymous hemianopia: contralateral lesion behind the optic chiasm. 

Incongruous homonymous hemianopia: suggests a relatively anterior retrochiasmal lesion, such as the optic tract. 

Increasingly congruous field defects: generally suggest progressively more posterior lesions. 

Homonymous hemianopia with macular sparing: classically suggests an occipital cortex lesion. 

27. Easy Localisation Sequence Think of the visual pathway from front to back: One eye only → retina or optic nerve. 

Temporal fields of both eyes lost → optic chiasm. 

Same side of visual field lost in both eyes → opposite retrochiasmal pathway. 

Superior quadrant lost → opposite temporal lobe. 

Inferior quadrant lost → opposite parietal lobe. 

Very congruous homonymous hemianopia ± macular sparing → opposite occipital cortex. 

Key Clinical Pattern The most useful rule is: PRE-CHIASM → ONE EYE. CHIASM → BITEMPORAL HEMIANOPIA. POST-CHIASM → CONTRALATERAL HOMONYMOUS FIELD LOSS. For the optic radiations: Temporal lobe → superior quadrantanopia → “pie in the sky.” Parietal lobe → inferior quadrantanopia → “pie on the floor.” And finally: Occipital cortex → highly congruous homonymous hemianopia, often with macular sparing.