Visual System, Optics and Ophthalmology

Question 1

Describe the optic nerve

Answer 1

CN II that terminates at the optic chiasm, but continuous with optic tract at the chiasm. It is approx. 4cm long and contains over 1 million axons.

Question 2

What is the optic chiasm?

Answer 2

It is formed by the crossing of the optic nerves within the brain.

Axons from the nasal field decussate here, while axons from the temporal field remain ipsilateral

Question 3

Describe the optic tract

Answer 3

• Extends from the optic chiasm to the lateral geniculate nucleus (LGN) in the thalamus (70% of fibres)
• Contains crossed and uncrossed fibres.
• 30% of axons leave the visual pathway before the LGN (i.e. pupillary light reflex - pretectal nuclei)

Question 4

Describe the geniculocalcarine tract

Answer 4

• Axons from the LGN to primary visual cortex
• The part of this tract that carries information from the inferior retina travels through the temporal lobe (Meyer’s Loop)
• The part carrying information from the superior retina travels through the parietal lobe (Baum’s Loop)