posterior segment of the eye

Question 1

the posterior segment of the eye comprises the back two-thirds of the eye, including:

Answer 1

• the vitreous humor
• the retina
• the choroid
• the optic disc

Question 2

what is vitreous

Answer 2

• transparent elastic hydrogel
• occupies ~80% of volume of the eye
• increased liquefaction with age

Question 3

what is the vitreous composed of

Answer 3

water (99%), collagen, hyaluronic acid, hyalocytes

Question 4

what are the functions of the vitreous

Answer 4

• vascularization of the lens (during embryogenesis)
• maintains ocular volume volume and shape
• can be surgically removed (by vitrectomy)

Question 5

layers of retina from outside in

Answer 5

• nerve fiber layer
• ganglion cell layer
• inner plexiform layer
• inner nuclear layer
• outer plexiform layer
• outer nuclear layer
• photoreceptor layer
• retinal pigment epithelium

Question 6

optical coherence tomography

Answer 6

non-invasive imaging of the retinal layers

Question 7

what are photoreceptors

Answer 7

• cells that initiate vision
• light activates opsin molecules that are stacked in discs in the outer segment

Question 8

cones

Answer 8

vision in bright light, color detection, visual acuity

Question 9

rods

Answer 9

vision in dim light

Question 10

what is phototransduction

Answer 10

• 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

Question 11

what is the retinoid cycle

Answer 11

• 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

Question 12

what are areas of specialization in the retina

Answer 12

• central areas of high RGC and cone density subserve higher visual acuity
• fovea and macula

Question 13

what is the choroid

Answer 13

• 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)

Question 14

what is the tapetum lucidum

Answer 14

a biologic reflector system to enhance visual sensitivity in dim illumination

Question 15

what is the optic disc

also called optic nerve head

Answer 15

• 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