Exam 2 -- Retina and Lens

Question 1

Name the ten layers of the retina (from outer to inner)

Answer 1

RPE, PRL, ELM, ONL, OPL (contains MLM), INL, IPL, GCL, NFL, ILM

Question 2

What is the role of AII cells?

Answer 2

Carries information from rod bipolars to ganglion cells

Question 3

Ellipsoid and myoid are two portions of photoreceptor inner segment. Which is inner, and which is outer? What does each contain?

Answer 3

Ellipsoid is outer and contains mitochondria, myoid is inner and contains golgi apparatus and ER.

Question 4

Where do dot and blot hemorrhages occur?

Answer 4

They occur in the inner nuclear layer.

Question 5

Approximately how many rods, cones, and ganglion cells do you have in each eye?

Answer 5

80-110 million rods, 4-5 million cones, and 1 million ganglion cells

Question 6

How large is the macula lutea, and where is it in relation to the optic disc?

Answer 6

Diameter is 5.5 mm; its center is 3.5 mm lateral to the edge of the disc and 1 mm inferior to the center of the disc

Question 7

What is the diameter of the fovea?

Answer 7

1.5 mm

Question 8

What is the diameter of the foveola? Thickness?

Answer 8

0.35 mm diameter, and 0.13 mm thickness

Question 9

What is the diameter of the rod-free zone?

Answer 9

0.57 mm

Question 10

What is the diameter of the capillary-free zone?

Answer 10

0.4-0.5 mm

Question 11

What is the width of the parafoveal area?

Answer 11

0.5 mm

Question 12

What is the width of the perifoveal area?

Answer 12

1.5 mm

Question 13

What is the diameter of the optic disc?

Answer 13

1.7 mm horizontally, and 1.9 mm vertically

Question 14

What marks the start of the parafoveal area?

Answer 14

When the INL is 12 cells thick and the GCL is 7 cells thick

Question 15

What marks the start of the perifoveal area?

Answer 15

When the GCL is 4 cells thick (it ends when the GCL is 1 cell thick.

Question 16

In fluorescein angiography, which part of the artery is seen first? Later, which part of the vein is seen first?

Answer 16

Artery: core (then wall); vein: wall (then core)

Question 17

True or false: rod bipolars are all ON

Answer 17

True.

Question 18

Do cone ON bipolars synapse on the flat parts of the pedicles or the invaginating parts?

Answer 18

Invaginating

Question 19

Do cone OFF bipolars synapse on the flat parts of the pedicles or the invaginating parts?

Answer 19

Flat

Question 20

What is the thickness of the unaccommodated lens?

Answer 20

3.5-5.0 mm (increases by 0.02 mm per year

Question 21

What is the diameter of the unaccommodated lens?

Answer 21

6.5 mm in infancy; increases to 9 mm by age 9 and thereafter remains constant

Question 22

Give a brief rundown of the phototransduction activation cascade.

Answer 22

Photon strikes 11-cis-retinal, causing it to isomerize to all-trans-retinal, which causes a conformational change of rhodopsin to metarhodopsin II. Metarhodopsin II activates transducin (a G protein). Transducin in turn stimulates PDE to hydrolyze cGMP, which closes cation channels. This leads to a reduction of glutamate release.

Question 23

Give a brief rundown of the phototransduction deactivation cascade.

Answer 23

G protein receptor kinase activation is increased through recoverin, which became activated through decreased calcium levels. GRK phosphorylates metarhodopsin II at the C terminal. Arrestin can then come and bind to the phosphorylated site to stop all rhodopsin activity. Meanwhile, low levels of calcium allow activation of guanylate cyclase (through GCAP1 and 2), which in turn replenishes cGMP in order to reopen the cation channels and reestablish the dark current.

Question 24

What are the important roles of calcium in the phototransduction process?

Answer 24

Low levels of calcium allows for activation of guanylate cyclase (through disinhibition of GCAP1 and 2), which reactivates cGMP.
Low levels of calcium also lead to activation of GRK (through disinhibition of recoverin), which helps inactivate rhodopsin.
Low levels of calcium also increase affinity of cation channels for cGMP.

Question 25

What do the following forms of vitamin A do in the visual system?

• Retinol
• Retinal
• Retinoic acid
• Retinyl ester

Answer 25

• Retinol = transport
• Retinal = visual transduction
• Retinoic acid = synthesis
• Retinyl ester = storage

Question 26

What are some of the components of the interphotoreceptor matrix?

Answer 26

Sulfated glycosaminoglycans*
Interphotoreceptor binding protein
Basic fibroblast growth factor
Hyaluronan, hyaluronan binding proteoglycans
MMPs

Question 27

In both the lens and the retina, the majority of glucose is anaerobically metabolized. True or false: in the retina, anaerobic glucose metabolism produces the majority of ATP, but in the lens, aerobic metabolism produces most of the ATP.

Answer 27

False. Retina ATP production from anaerobic metabolism is relatively low at 13%, even though the anaerobic metabolism is 60% of the glucose. In the lens, anaerobic metabolism does indeed produce the most ATP (60% ATP production, 80% glucose usage).

Question 28

The RPE is associated with a lot of growth factors. What is PEDF, where is it expressed, and what does it do?

Answer 28

Pigment epithelium-derived factor; it is expressed on the neural side of the RPE; it protects neurons against glutamate-induced or hypoxia-induced apoptosis. It is an antiangiogenic factor that inhibits endothelial cell proliferation.

Question 29

The RPE is associated with a lot of growth factors. What is VEGF, where is it expressed, and what does it do?

Answer 29

Vascular endothelial growth factor; it is expressed on the choriocapillary side of the RPE; it prevents endothelial cell apoptosis and is essential for intact choriocapillaris endothelium. It is also a permeability stabilizing factor for the fenestrations of the endothelium.

Question 30

The apical side of the RPE contains more potassium and has the sodium-potassium pumps, making this side more positive. The basolateral side has chloride channels, making this side more negative. True or false: RPE transports water and ions toward the choriocapillaris and glucose and other nutrients (vitamin A) toward the retina.

Answer 30

True.

Question 31

What is the lens capsule made of? What is its function? What syndrome affects one of these components?

Answer 31

Laminin and collagen IV. It functions as an anchor point for lens epithelial cells and also provides signals for these cells to proliferate, migrate, and differentiate. Alport syndrome is caused by a genetic mutation in the genes that regulate collagen synthesis.

Question 32

What are the characteristics of Alport syndrome?

Answer 32

Glomerulonephritis, hearing loss, lenticonus. (It can also present with dot and fleck retinopathy.)

Question 33

True or false: the microcirulation of the lens is characterized by flow in through the equator and out through the poles.

Answer 33

False; entry is at the poles and exit is at the equator.

Question 34

True or false: iron is good for the lens

Answer 34

False; higher levels of iron are associated with more reactive oxygen species that can contribute to cataract formation. Inflammation can increase iron concentration. (Iron is transported by transferrin and stored by ferritin.)

Question 35

What does ascorbate do?

Answer 35

It plays a role in protecting the lens against oxidants. Its concentration is higher in the lens than in the plasma.

Question 36

Crystallin protein is found in the lens. There is alpha, beta, and gamma types, and alpha has two subtypes (A and B). Which of the alpha subtypes is more abundant in the lens fibers, and which is in the epithelial cells? What do these subtypes do?

Answer 36

Alpha-A is in the fibers, and Alpha-B is in the epithelial cells. These acts as heat-shock proteins and ensure proper folding of proteins. They also inhibit apoptosis. (Alpha-B has been shown in Lewy bodies, which are associated with Parkinson’s and Alzheimer’s diseases.)

Question 37

How do Beta and Gamma crystallins work together? Which of these is more prone to oxidative stress?

Answer 37

They form dimers together (having a Greek key motif), functioning to allow dense packing of proteins in order to minimize light scatter. Gamma has a lot of cysteines that can potentially form disulfide bonds, so it is more prone to oxidative stress.

Question 38

What are the different types of post-translational modifications that can occur with crystallins?

Answer 38

Ser, Thr, Tyr phosphorylation
Arg and Lys methylation
Lys acetylation
Met, Tyr, and Trp oxidations

Question 39

Which of the crystallin types (Alpha, Beta, or Gamma) is the largest? Which is the most abundant?

Answer 39

Alpha is the largest; Beta is the most abundant.

Question 40

In terms of cataracts, you can have (in terms of prevalence) nuclear sclerotic, cortical cataract, and subcapsular cataract (usually found posterior). What causes posterior subcapsular cataracts?

Answer 40

Epithelial cells that fail to properly differentiate into fibers. Steroids can cause posterior subcapsular cataracts, as can diabetes and defects of galactose metabolism.