Optic Pathway & Visual Fields

Contralateral projection to retinaThe visual field for each eye can be split into two part s: nasal field and temporal field. Each will project to the opposite side of the retina

RIGHT

LEFT VISUAL FIELD

Medial/Nasal

Temporal

the optic pathway

Understanding optic nerve anatomy and visual pathways is key to appreciating how focal lesions of the brain cause visual field defects.

Optic NerveThe optic nerve (CNII) will transmit the special sensory infomation for vision for each ipsilateral eye.

Pre-chiasmal

Optic ChiasmLeft and right optic nerves converge at the optic chiasm, located directly above the sella turcica of the sphenoid bone. Here fibres from the nasal aspect of each retina decussate to the contralateral optic tract, while fibres from the temporal retina remain on their respective sides.

Chiasmal

Optic TractsThe optic tracts extend from the chiasm to the thalamus, and contains contralateral nasal fibers and ipsilateral temporal fibers.

Pre- tectal nucleus

Lateral Geniculate Nucleus (Thalamus)The optic tracts terminate in the lateral geniculate nucleus (LGN) of the thalamus, where afferent sensory nerves from the eye synapse with the second-order sensory neurones that radiate dorsally to the calcarine sulcus of the occipital lobe.

Post-chiasmal

Superior Colliculus (midbrain)

Optic RadiationsCourse between the LGN to the ipsilateral primary visual cortex (calcarine sulcus) Optic radiations loop either through the parietal lobe or through the temporal lobe

Calcarine sulcus (occipital lobe)Optic radiations terminate in the calcarine sulcus, where the cortical visual centre is situated. Radiations coursing through the parietal lobe correspond to upper half of the retina/lower visual field, while Meyer's loop (temporal lobe) correspond to the bottom half of the retina/upper visual field

CALCARINE SULCUS PROJECTIONS

VISUAL FIELD deficits

Click on each location or structure implicated by a lesion, to learn about the visual deficit

RIGHT

LEFT VISUAL FIELD

Medial/Nasal

Temporal

1. Left Optic Nerve Lesion

Deficit: Left anopia (total vision loss in the left (ipsilateral) eye)

Pre-chiasmal

Want to learn about the causes of an OPTIC CHIASM lesion?? Click on the star icon

2. Optic Chiasm (Central)

Deficit: Bitemporal hemianopiaLoss of vision in the temporal fields (both eyes)

Chiasmal

3. Left Optic Tract

Deficit: Right homonymous hemianopia (Posterior to chiasm, deficits are contralateral)

Post-chiasmal

4. Left Optic Radiations

Deficit: Right homonymous quadrantanopiaMeyer's Loop - upper quadrantanopia (“pie in the sky”) Parietal Loop - lower quadrantanopia (“pie on the floor”)

Lesion to Meyer's loop = upper homonymous quadrantanopia

Lesion to Parietal radiations = lower homonymous quadrantanopia

5. Left Calcarine Cortex

Deficit: Right homonymous hemianopia with sparing of the macula (Macular vision is spared given the dual blood supply by PCA and MCA)

Location of Lesions

Pre-chiasmal

Lesions that occur anterior to the optic chiasm, will result in vision loss of the ipsilateral affected eye (right eye example)

Chiasmal

Lesions that occur at the level of the optic chiasm, will cause vision loss in the temporal fields of both eyes

Lesions that occur posterior to the optic chiasm (e.g. optic tracts, LGN, optic radiations or visual cortex) will cause homonymous visual defects - where the same region in the visual field of each eye is affected (quadrants or halves)

Post-chiasmal

Pituitary Adenoma (Tumour)

Compression of the optic chiasm, due to a pituitary adenoma as seen in the MRI (or suprasellar aneurysm), can cause bilateral temporal hemianopsia due to disruption of the pathways transporting information from the nasal part of the retina. The nasal part of the retina receives sensory info from the temporal vision fields.

Sensory information from the lower visual field, projects to the upper retina. This will travel along fibres which course through the parietal lobe, to synapse above the calcarine sulcus (green)

Sensory information from the upper visual field, projects to the lower retina. This will travel along fibres which course around the inferior horn of the lateral ventricle in the temporal lobe, via Meyer's loop, to synapse below the calcarine sulcus (blue)