Cranial Nerve II – Optic Nerve & Visual Pathways

A comprehensive set of flashcards covering anatomy, pathways, clinical examination, and common pathologies related to Cranial Nerve II and visual function.

Which cranial nerve is responsible for the special sense of vision?

Cranial Nerve II – the Optic nerve.

What type of tissue is the retina considered to be?

A direct extension of cerebral tissue.

What do rods in the retina primarily detect?

Differences between light and dark (brightness).

Where are cones most densely concentrated?

In and near the fovea centralis.

Which retinal quadrants perceive the right visual field?

The left retinal quadrants (superior & inferior).

Where do all retinal ganglion cell axons converge before exiting the eye?

At the optic disc.

Through which bony canal does each optic nerve leave the orbit?

The optic canal of the sphenoid bone.

At the optic chiasm, which retinal fibres cross?

Nasal (medial) retinal fibres.

After the chiasm, what does the right optic tract contain?

Visual information from the right retinal fields of both eyes.

Which thalamic nucleus receives input from the optic tract?

The lateral geniculate nucleus (LGN).

What are the two parts of the dorsal optic radiations?

Baum’s loop (superior) and Meyer’s loop (inferior).

Baum’s loop carries information from which retinal quadrants and visual fields?

From superior retinal quadrants → inferior visual fields.

Meyer’s loop carries information from which retinal quadrants and visual fields?

From inferior retinal quadrants → superior visual fields.

Where do optic radiations terminate?

Primary visual cortex on either side of the calcarine sulcus.

Which part of the calcarine sulcus maps peripheral vision?

More anterior (proximal) regions.

What pupil characteristic might suggest posterior synechiae (uveitis)?

Abnormally shaped pupil (not round).

Anisocoria that is more pronounced in bright light suggests what lesion?

Oculomotor nerve palsy (larger pupil is abnormal).

Anisocoria more obvious in the dark suggests what syndrome?

Horner’s syndrome (smaller pupil is abnormal).

Standard distance for a Snellen chart visual-acuity test?

6 metres (20 feet).

What does improvement with a pinhole test indicate?

A refractive error is contributing to poor vision.

Give three common causes of decreased visual acuity.

Refractive errors, cataract, optic neuritis (others: amblyopia, macular degeneration).

Define the direct pupillary light reflex.

Constriction of the illuminated pupil when light is shone into it.

Define the consensual pupillary light reflex.

Constriction of the opposite pupil when light is shone into one eye.

Which midbrain nucleus is the afferent relay for the light reflex?

The pre-tectal nucleus.

Which parasympathetic nucleus provides efferent fibres for pupil constriction?

Edinger-Westphal nucleus (via CN III).

What clinical test detects a relative afferent pupillary defect (RAPD)?

The swinging light test.

What is another name for a relative afferent pupillary defect?

Marcus-Gunn pupil.

List two optic-nerve–related causes of RAPD.

Optic neuritis, advanced unilateral glaucoma (also central retinal artery/vein occlusion).

How does an isolated oculomotor nerve palsy affect the pupil?

Ipsilateral pupil is dilated and non-reactive, but consensual reflex in the other eye remains.

What tool is standard for colour-vision screening?

Ishihara plates.

Name an acquired cause of red-green colour vision loss.

Optic neuritis (other: vitamin A deficiency, chronic solvent exposure).

What neurological condition often causes visual neglect?

Parietal lobe injury (e.g., post-stroke).

How is visual extinction demonstrated during a neglect test?

Patient misses one moving finger when both sides are stimulated simultaneously but sees each when tested alone.

During confrontation testing, what does bitemporal hemianopia indicate?

Lesion at the optic chiasm (often pituitary tumour).

Homonymous hemianopia results from lesions located where?

Posterior to the optic chiasm (optic tract, radiations, or occipital cortex).

Define scotoma.

An island of vision loss surrounded by areas of normal vision.

What physiological reason creates everyone’s blind spot?

Lack of photoreceptors where the optic nerve exits at the optic disc.

Give one retinal and one optic-nerve cause of an enlarged blind spot.

Retinal detachment; optic neuritis (others: glaucoma, macular degeneration).

Why is fundoscopy performed in a cranial-nerve II exam?

To inspect the optic disc for pathology such as papilloedema.