posterior segment of the eye Flashcards
the posterior segment of the eye comprises the back two-thirds of the eye, including:
- the vitreous humor
- the retina
- the choroid
- the optic disc
what is vitreous
- transparent elastic hydrogel
- occupies ~80% of volume of the eye
- increased liquefaction with age
what is the vitreous composed of
water (99%), collagen, hyaluronic acid, hyalocytes
what are the functions of the vitreous
- vascularization of the lens (during embryogenesis)
- maintains ocular volume volume and shape
- can be surgically removed (by vitrectomy)
layers of retina from outside in
- nerve fiber layer
- ganglion cell layer
- inner plexiform layer
- inner nuclear layer
- outer plexiform layer
- outer nuclear layer
- photoreceptor layer
- retinal pigment epithelium
optical coherence tomography
non-invasive imaging of the retinal layers
what are photoreceptors
- cells that initiate vision
- light activates opsin molecules that are stacked in discs in the outer segment
cones
vision in bright light, color detection, visual acuity
rods
vision in dim light
what is phototransduction
- conversion of light into a change in the electrical potential across the photoreceptor cell membrane
- it turns OFF the circulating dark current in photoreceptors
- results in inhibition of glutamate release
what is the retinoid cycle
- photon capture causes isomerization of 11-cis-retinal to all-trans-retinal
- the retinoid (=visual) cycles regenerate 11 cis-retinal through a series of enzymatic reactions
what are areas of specialization in the retina
- central areas of high RGC and cone density subserve higher visual acuity
- fovea and macula
what is the choroid
- posterior component of the uvea
- layer of blood vessel and connective tissue
- located between retina and sclera
- provides nutrients and O2 to outer layers of the retina via the fenstrated capillary bed (choriocapillaris)
what is the tapetum lucidum
a biologic reflector system to enhance visual sensitivity in dim illumination
what is the optic disc
also called optic nerve head
- myelination/shape varies across species
- retinal arterioles and veins emerge from its surface
- site where axons of RGCs exit the eye to form the optic nerve
- the lamina cribrosa is a collagen structure that provides a structural support to RGC axons as they leave the eye