Retina in Cross Section
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Vitreous Cavity:
- Filled with clear gel called “vitreous humor”
- Vitreous humor (usually just called “vitreous”) made up of hyaluronic acid, collagen fibers, and dilute salt water solution
- Collagen is thickest in peripheral portion called “vitreous cortex”
- Vitreous cortex has firm attachments to anterior retina and border of optic disc
- With aging, inflammation, high myopia, or trauma, vitreous degenerates into lakes of water that place stress on its attachments to retina, and…
- Vitreous detaches itself from optic disc, leaving floater, and…
- Peripheral vitreous cortex detaches from retina, sometimes tearing hole in retina
- If fluid seeps under retinal hole, retina may detach
- Retinal detachment must be emergently repaired surgically to preserve vision
Lens:
- protein-rich, bean-shaped structure suspended by zonular ligaments
- responsible for 1/3 of refracting power of eye (the cornea accounts for 2/3)
- opacification (cataract) occurs with advancing age, inflammation, or trauma
- can be removed surgically without harming eye and replaced with clear artificial implant ("intraocular lens’)
Ganglion Cell:
- Conveys visual signals through optic nerve to lateral geniculate body in thalamus
Bipolar Cell:
- Way station in neural pathway from rods and cones to ganglion cells
Rod:
- Photoreceptor that transduces light into neural signals responsible for vision in low light situations
Cone:
- Photoreceptor that transduces light into neural signals responsible for high-resolution and color vision
Retinal pigment epithelium:
- Single layer of hexogonal cells that provides metabolic support to rods and cones (photoreceptors)
- Tight junctions between retinal pigment epithelial cells form outer blood-retinal barrier, which prevents macromolecules that escape from choroidal vessels from entering retina
Macula:
- Retinal region containing high density of cones and ganglion cells specialized in visual acuity and color vision
Choroid:
- Vascular nutrient layer of outer retina (including retinal pigment epithelium and rods and cones)
Sclera:
- Collagenous outer layer of wall of eye
- Superficial portion, called episclera, has rich vascular network.
- Bilirubin accumulates in episclera to stain sclera yellow ("icterus").
- Becomes inflamed in connective tissue diseases. See Common Ophthalmic Manifestations of Various Rheumatic (connective tissue) Diseases.
Optic nerve:
- Contains retinal ganglion cell axons travelling to optic chiasm and on to lateral geniculate body
Fovea:
- Central depression within macula in which retina consists only of cones
- Foveal pit comes about because other retinal tissue is pushed aside so light can travel directly to cones
Retinal artery & vein:
- Vessels that travel in innermost retinal layer
- Arteries nourish only retinal ganglion cells and their axons (deeper layers get blood from choroid)
Retina:
- Inner layer of posterior wall of eye
- Nutrient retinal pigment epithelial forms outer portion and neurosensory layers form inner portion
Choroid:
- Vascular nutrient layer of outer retina (including retinal pigment epithelium and rods and cones)
Sclera:
- THIS ONE! Collagenous outer layer of wall of eye
- Superficial portion, called episclera, has rich vascular network.
- Bilirubin accumulates in episclera to stain sclera yellow ("icterus").
- Becomes inflamed in connective tissue diseases. See Common Ophthalmic Manifestations of Various Rheumatic (connective tissue) Diseases.