Where is the central retinal artery (CRA) seen with a fundoscope?

Location of the Central Retinal Artery on Fundoscopic Examination

The central retinal artery is seen at the optic disc where it emerges from the center of the disc and branches into superior and inferior divisions that further divide to supply the four quadrants of the retina. 1

Anatomical Considerations

The central retinal artery (CRA) has a specific anatomical course before it becomes visible on fundoscopic examination:

• The CRA originates from the ophthalmic artery, which is the first branch of the internal carotid artery 1
• It enters the optic nerve sheath approximately 18.6 mm distal to the optic canal 2
• More than 70% of CRAs penetrate near the midline of the lower surface of the optic sheath 2
• After traveling within the optic nerve, the CRA emerges at the center of the optic disc 1

Fundoscopic Appearance

When examining the fundus with an ophthalmoscope, the CRA can be identified by these characteristics:

• The CRA emerges from the center of the optic disc 1
• It immediately divides into superior and inferior branches at the optic disc 1
• These branches further divide into nasal and temporal branches, creating four main branches that supply the four quadrants of the retina 1
• The arteries appear bright red and narrower than the accompanying veins 1
• The arteries can be distinguished from veins by their:
  • Brighter red color
  • Smaller caliber
  • More distinct vessel wall reflection
  • Less tortuosity compared to veins

Clinical Significance

Understanding the normal appearance and location of the CRA is critical for diagnosing several conditions:

• Central retinal artery occlusion (CRAO) presents with:

  • Retinal whitening (edema)
  • Cherry red spot at the fovea
  • Attenuated (narrowed) retinal arteries 1
  • Poor visual prognosis with low chance of spontaneous visual recovery 3

• Branch retinal artery occlusion affects only one branch of the CRA, causing segmental retinal whitening 1

• Emboli (Hollenhorst plaques) may be visible within the CRA or at arterial bifurcations 1

  • These appear as bright refractile bodies within the vessel lumen
  • Their presence should prompt evaluation for systemic atherosclerotic disease 1, 4

Anatomical Variants

Important variants to be aware of when examining the fundus:

• In approximately one-third of eyes, a cilioretinal artery is present 1

  • This artery originates from the posterior ciliary circulation, not the CRA
  • It often supplies the fovea, which is critical for central vision
  • When present, it may preserve central vision in cases of CRAO 1, 5

• In some cases, the upper and lower retinal arteries may emerge separately from the optic disc rather than as branches of a single central trunk 5

Understanding the normal appearance and location of the CRA is essential for prompt recognition of vascular occlusions that require urgent evaluation and management, as CRAO is considered an ocular emergency equivalent to cerebral stroke 6, 3.