Retina & Optic Nerve Through Ophthalmoscope
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Physiologic cup:
- Central depression within optic disc containing no retinal ganglion cell axons
- Encircled by neuroretinal rim tissue carrying retinal ganglion cell axons
- Floor bridged by sieve-like scleral lamina cribrosa
- Ratio of cup diameter to total disc diameter called “cup-to-disc ratio”
- Cup-to-disc ratio very variable, but does not normally exceed 0.5
- When cup-to-disc ratio exceeds 0.5, consider glaucoma
Fovea:
- Depression in retina surface consisting only of cone photoreceptors
- Damage leads to reduction in visual acuity and sometimes color vision
- Common disorders are age-related macular degeneration and diabetes
Macula:
- Retinal region centered at fovea and extending nearly to optic disc and temporal vascular arcades
- Contains high density of cones and ganglion cells specialized in visual acuity and color vision
- Often damaged by age-related macular degeneration, diabetes, and many other disorders
- Damage often visible as change in color from orange to red, yellow, white, or black
Retinal artery:
- Nourishes retinal ganglion cells and axons (deeper retinal layers are fed by choroidal arteries)
- Occlusion often caused by hypertension, arteriosclerosis, diabetes, hypercoagulable disorders, and embolism from cervical carotid artery
- Occlusion causes patchy change in color from orange to white in retinal region served by occluded vessel (“ischemic retinal whitening”)
Retinal vein:
- Drains blood from superficial retina nourished by retinal artery
- Occlusion often caused by hypertension, arteriosclerosis, diabetes, and hypercoagulable disorders
- Occlusion visible as patches of blood scattered across retinal surface
Neuroretinal rim:
- Optic disc tissue that surrounds physiologic cup
- Carries axons of retinal ganglion cells
- May be damaged by inflammation (“optic neuritis”), ischemia (“ischemic optic neuropathy”), increased intracranial pressure (“papilledema”), toxins, medications, metabolic disorders, orbital or intracranial tumors, congenital disorders, and glaucoma
- Inflammation, ischemia, and increased intracranial pressure usually cause swelling
- Orbital and intracranial tumors usually cause pallor
- Congenital disorders usually cause reduced size (“hypoplasia”)
- Glaucoma usually causes enlargement of physiologic cup as neuroretinal rim tissue withers (“pathologic cupping”)