Optic disc (optic nerve head)
Optic nerve · detail · Enlarged blind spot
The point where unmyelinated ganglion-cell axons converge and turn backwards through the lamina cribrosa, accompanied by the central retinal vessels. It has no photoreceptors, so it produces the physiological blind spot about 15 degrees temporal to fixation.
Traced from the start
- Temporal hemiretinaNasal hemiretinaMacula and papillomacular bundle
- Optic disc (optic nerve head)
Detail
- Blind spot
- About 15 degrees temporal to fixation in each eye's field
- Vessels
- Central retinal artery and vein enter and leave through the disc
- Swelling mechanism
- Raised CSF pressure in the nerve sheath blocks axoplasmic flow at the lamina cribrosa
When it goes wrong
Raised intracranial pressure transmitted along both nerve sheaths (papilloedema)
Bilateral disc swelling with enlarged blind spots and transient visual obscurations; acuity preserved until late and no RAPD unless asymmetric
Chronic open-angle glaucoma damaging axons at the lamina cribrosa
Arcuate scotomas and a nasal step progressing to tunnel vision, with an increased cup-to-disc ratio; central acuity spared until late
Central retinal artery occlusion (embolus, giant cell arteritis)
Sudden painless profound monocular loss with a dense RAPD; an emergency
Practise this structure
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