Vision 1,2,3,4

Front 1

12 major functions of the eye?

Back 1

1. phototopic vision (day vision): 6.8 million cones, central, color, high resolution
2. scotopic vision (night vision): 125 million rods, black/white, peripheral, low resolution
3. control amount of light entering eye (miosis or mydriasis)
4. keep visual world in focus (near synkinesis)
5. keep eyes focussed on point during head movement (vestibular input)
6. sense light cycles for circadian rhythms
7. interpret "where and what"
8. calculate depth perception (stereopsis)
9. fusion (eyes looking straight ahead; sensory loop and motor loop)
10. conjugate eye movements
11. creates retinotopic map
12. create darkroom via melanin

Front 2

What is the vitreous body?

Back 2

-4 ml, consistency of raw egg whites
-mostly water, strands of collagen type i, polymers of hyaluronic acid
-extends from inner surface of stratified neural retina to posterior capsule of lens
-with normal aging, becomes liquefied so that retinal detachments are more prevalent in the elderly

Front 3

RPE vs. neural retina

Back 3

-RPE- retinal pigment epithelium is the "life line" of the neural retina
-RPE located at back of eye, just below choroid layer; neural retina then begins with many layers
-RPE functions:
1) create the blood-photoreceptor barrier and become the nutrient barrier for the outer retina
2) daily phagocytoss of outer segment discs
3) vit A metabolism (reisomerization from trans back to cis for rods; cones can do it themselves)
4) melanin production for high visual acuity
5) neovascular barrier to hold back the constant desire of the choroidal vasculature to neovascularize into the subretinal space
neural retina is 0.1 mm thick and stratified with photoreceptors, horizontal cells, bipolar cells, amacrine cells, X,Y,Z ganglion cells, and muller cells

Front 4

What is the near synkinesis reflex?

Back 4

1. accommodation (parasympathetic CN III)
2. convergence (CN III on medial recti muscles)
3. miosis (parasympathetic CN III)

Front 5

7 innervation cites of CN III?

Back 5

medial rectus, inferior rectus, superior rectus, inferior oblique, levator palpebrae, ciliary body for accommodation, circular contrictor muscle

Front 6

List the morphologic facts which explain the high resolution of the foveola in the retina.

Back 6

The foveola is the point of highest visual acuity because it concentrates tiny, small diameter cones for higher resolution and because the neural retina is thinnest here (least amnt of light distortion). All retinal neurons are tiny compared to other cns neurons otherwise the eye would be the size of a grape fruit. Light does not have to dodge the inner retinal vasculature or second or thir order neurons to reach the foveolar cones because they are laterally displaced. In addition, there is little convergence; one photoreceptor synapses with one bipolar cell which synapses with one ganglion cell.

Front 7

What holds the neural retina adjacent to the apical surface of the RPE preventing retinal detachments?

Back 7

1. RPE microvilli interdigitate with photoreceptor outer segments
2. a mucopolysaccharide matrix glue in the subretinal space
3. a cone outer segment domain of mucus
4. a water flux from the vitreous across the cellular resistance of the neural retina into the choroidal vessels driven by the RPE ionic pumps
5. the jelly-like nature of the vitreous body

Front 8

Describe the ERG.

Back 8

Electroretinogram appraises photopic and scotopic vision in whole or part of retina. An electrode is placed on sclera and another on forehead. With a pulse of light, revleals 3 aspects:
-a wave depression relates to photoreceptor function
-b wave relates to bipolar function
-c wave relates to RPE function

Front 9

Describe the two sources of vasculature in the retina.

Back 9

The outer retina (to photoreceptors) supplied by the choroidal vessels (from long posterior ciliary artery); entire inner retina (bipolar and ganglion) supplied by the inner retinal vasculature (supplied by central retinal artery)

Front 10

Contrasting points of photoreceptors and hair cells:

Back 10

1. second messages vs. brownian motion: photoreceptors become activated by a series of messages (rhodopsin, gtp, glutamate) whereas the hair cells use no second messages. Thus, the photoreceptors require extensive vasculature whereas the hair cells require scarce vasculature.
2. connecting cilia vs. the kinocilium: photoreceptors have 9+0 cilia with no motor proteins that connect the outer and inner segments. Its function is critical in organizing disc formation at the base of the outer segment. This is in contrast to the 9+2 immotile cilia of hair cells that determine the axis of bilateral symmetry, height of the hair bundle, and diameter of stereocilia.
3. Outer segment discs vs. the hair bundle: outer segment discs have eternal youth: We make 100 new discs (each of rod and cone types) per day; the oldest 100 rod discs are phagocytized and degraded by the RPE every morning and the oldest cone discs are phagocytized and degraded by the RPE each night. In contrast, we make hair cells once in our life and have to rely on 5 enzymes to maintain them.
4. RPE vs. accessory structures:
RPE functions:
1) create the blood-photoreceptor barrier and become the nutrient barrier for the outer retina
2) daily phagocytoss of outer segment discs
3) vit A metabolism (reisomerization from trans back to cis for rods; cones can do it themselves)
4) melanin production for high visual acuity
5) neovascular barrier to hold back the constant desire of the choroidal vasculature to neovascularize into the subretinal space

This contrasts with the inert accessory structures above the hair bundles (cupula in critae, otolithic membrane with otoconia above the macula of the utricle and the macula of the saccule, tectorial membrane)

Front 11

What are the pathologies related to the two vasculatures of the retina?

Back 11

choroidal vasculature-retinal detachment will kill photoreceptors quickly since they have a high metabolic demand (due to the ellipsoid mitochondria) provided by the choroidal vessels

inner retinal vasculature- capillary bed breaks down during diabetic retinopathy

Front 12

Describe amplification in the retina

Back 12

Light activates rhodopsin which ctivates transducin to bing GTP. This activates phosphodiesterase which catalyzes conversion of cGMP to 5'-GMP.

cGMP usually keeps Na channels open so that photoreceptors are tonically depolarized and releasing glutamate>with drop in concentration of cGMP, Na channels close, photoreceptors hyperpolarizes and electrical pathways within retina are activated for vision

called amplification because one rhodopsin molecule causes hundreds of outer segment Na channels to close

Front 13

Describe the 3 types of ganglia

Back 13

X/parvocellular/p pathway- 40% of ganglion neurons; tiny dendritic field; used for fine detail, high acuity, color; synapse in LGN; code for "what" vision in temporal lobe

Y/magnocellular/M pathway- 40% of ganglions; medium sized dendritic field; detect motion and general shape, "primal sketch"; synapse in LGN; code for "where" of vision in frontal lobe

W pathway- 20% of ganglions; enourmous denritic field; detect light levels, not visual acuity; synpase in either suprachiasmatic nucleus of hypothalamus for circadian rhythms, or pretectal/superior colliculus area bilaterally to drive Edinger-Westphal nucleus to control pupil size

Front 14

Cause and result of age-related macular degeneration?

Back 14

phagocytized disc material called drusen aka "lysosomal shit" drains and accumulates at basal surface of RPE (btw RPE and choroid)

Results in death of RPE then cones then neovascularization intosubretinal space which kills more photoreceptors