Biochem- The eye

Question 1

Where is anaerobic glycolysis the main source of energy in the eye? How about oxidative metabolism?

Answer 1

• Anaerobic in the lens
• Aerobic in the retina and cornea (but only slightly)

Question 2

An accumilation of what substance will cause corneal clouding?

Answer 2

Glycosaminoglycans

(Hurler and Sly syndromes)

Question 3

How is water balance within the cornea maintained?

Answer 3

-by the hypertonic nature of the aqueous humor and active pumping of HCO3- out of the cornea

Question 4

What is the purpose of VEGFR-3 on the anterior epithelial layer of the cornea?

Answer 4

-prevents the growth of blood vessels into the cornea by neutilizing growth factors

Question 5

Why is NADPH so important in the cornea?

Answer 5

-to prevent or reduce photo-oxidation through the GSH (glutathione) reductase pathway

Question 6

How does glucose get to the cornea> How about oxygen?

Answer 6

• Glucose diffuses through the aqueous humor
• Oxygen diffuses through the anterior surface through the tears

Question 7

How does prolonged contact lens wear cause corneal swelling?

Answer 7

-causes hypoxia beneath the lens which results in increased lactate production and decreased corneal pH

Question 8

What is the main purpose of the aqueous humor?

Answer 8

-to bring nutients to the cornea and lense and remove end products to the blood stream

Question 9

How is aqueous humor secreted? Reabsorbed?

Answer 9

• Secreted by ciliary process through secretion of Na, Cl and bicarb which water follows. Glucose, AA, and ascorbic acid are actively transported into the aqueous humor.
• it drains into the blood stream through the canal of schlemm

Question 10

Is the vitreous humor a free flowing fluid?

Answer 10

no. it is a gelatinous mass

Question 11

What is the major makeup of the vitreous humor?

Answer 11

99% water

-mostly Type II collagen, proteoglycans, and hylauronic acid

Question 12

What is posterior vitreous attachment?

Answer 12

-with old age the vitreous becomes more liquid like and can separate from the retina

(floaters and flashes of light)

Question 13

What is the most common cause of glaucoma?

Answer 13

-increased IOP due to a decrease in the drainage of the aqueous humor

Question 14

Can glaucome result from someone who has a normal IOP?

Answer 14

Yes, it is called normal tension glaucoma

Question 15

What is the most common form of glaucoma?

Answer 15

primary open angle glaucoma–> decrease in the rate of drainage of aqueous humor

Question 16

How is open angle glaucoma most commonly treated?

Answer 16

With the use of:

• protaglandin analogues (Xalantan)
• ß-blockers (Timolol)
• and Cholinergic agonists for acute attacks (Pilocarpine)

Question 17

How would a carbonic anhydrase inhibior help in the treatment of open angle glaucoma?

Answer 17

-Decreased secretion of bicarb results in decreased aqueous humor production

Question 18

What is the cuase of closed angle glaucoma? How is it treated?

Answer 18

• the outer edge of the iris protrudes over the drainage canals
• surgical removal of that part of the iris

Question 19

What are som erisk factors for glaucoma?

Answer 19

• African
• family history
• diabetes
• severe myopia
• steroid use
• previous eye injury

Question 20

How does the lens receieve nutients/dump waste?

Answer 20

-through the aqueous humor

Question 21

What is a cataract? What are some risk factors?

Answer 21

• opacity of the lense caused by an aggregation of proteins
• diabetes, galactosemia, radiation, smoking, high fat dies, genetic

Question 22

How does excess sugar in the lense contribute to cataracts?

Answer 22

• Glucose is reduced to sorbitol
• sorbitol accumilation leads to an increased uptake of water–> when the crystallins become more hydrated they become less soluble in the lens

Question 23

What causes cataract formation in a galactosemic infant?

Answer 23

• galactose is reduced to galactitol
• Galactitol has the same effect as sorbitol and draws water into the lense–> reduced crystalline solubility

Question 24

What is the first sign of cataract formation in an individual who has recieved radiation (x-ray)?

Answer 24

-Sharp decrease in reduced glutathione

Question 25

How does oxidative damage lead to the formation of cataracts?

Answer 25

Oxidation of sugars produces compound that can cause the oxidation of glutathione and other proteins and inhibit the pentose phosphate pathway.

Question 26

What is the cause of senile cataracts?

Answer 26

• Old-ness
• modification and breakdown of proteins, reduction in glutathione levels and changes in membrane permeabilities.

Question 27

What is the major inherited mutation leading to cataract formation?

Answer 27

-premature formation from mutations in chaperone proteins which results in misfolded lens proteins

Question 28

What areas of the retina are involved with oxidative metabolism? How about anaerobic metabolism?

Answer 28

• The vascular portions (oxidative)
• Fovea has no vessels as well as the outer segments of rods and cones (anaerobic)

Question 29

What is the leading cause of blindness in the eldery?

Answer 29

-Age related macular degeneration (AMD)

Question 30

What are the two forms of AMD?

Answer 30

Wet and Dry

Question 31

What is Dry AMD?

Answer 31

-cells of the macula slowly breakdown and develop yellow deposits called Drusen

Question 32

What is wet AMD?

Answer 32

blood vessels grow in beneath the macula and leak blood

Question 33

What is the treatment for Dry AMD? how about Wet AMD?

Answer 33

-Dry: no effective treatment (some antioxidant vitamins and minerals may help)

Wet: injections of VEGF inhibitors may arrest the progression of the disease (also Laser)