Optic Tract

Optic Tract

The optic tracts are important components of the visual pathway, transmitting visual information from the optic chiasm to the lateral geniculate nucleus of the thalamus. After fibres from the nasal retina cross within the optic chiasm, the optic tracts carry visual information from the contralateral visual field to higher visual processing centres. Integrity of the optic tracts is essential for normal visual perception, and damage can result in characteristic visual field deficits. Because of their critical role in visual function, accurate delineation of the optic tracts is important when assessing and minimizing radiation dose to the visual pathway. Careful contouring can support treatment planning, toxicity evaluation, and research into radiation-induced visual complications.

For contouring, the left and right optic tract should be delineated separately. Co-registration with a T1-weighted MRI is recommended to facilitate accurate identification of the structure. The optic tract originates at the posterolateral aspect of the optic chiasm and extends posteriorly towards the lateral geniculate nucleus. On MRI, it typically appears as a slender linear structure coursing posteriorly, lateral to the hypothalamus and medial to the anterior perforated substance.

Key anatomical landmarks include:

• Anterior border: posterolateral aspect of the optic chiasm.
• Medial border: hypothalamus.
• Lateral border: anterior perforated substance.
• Posterior extent: towards the lateral geniculate nucleus within the thalamic region.

The optic tract is generally best visualized close to the optic chiasm. Visibility often decreases beyond the first 10–15 mm of its course. Contouring should therefore continue only while the structure can be confidently identified on imaging. Posteriorly, the contour may extend towards the thalamus but should be stopped once the optic tract is no longer clearly distinguishable from the surrounding tissues.

The accompanying video demonstrates a step-by-step approach for identifying and contouring the optic tract using anatomical landmarks on MRI. This educational resource is intended to support consistent, accurate, and reproducible delineation for clinical and research applications.

Please site as follows:

Hofstede, D., Di Perri, D., Roelofs, E., Postma, A., Troost, E., & Eekers, D. EPTN International Neurological Contouring Atlas (INCA) instruction videos. CancerData, 2022. doi:10.17195/candat.2022.02.1