Test 20 (ocular physiology)

1. The retinal pigment epithelium (RPE):

a. is sensitive to hypervitaminosis A

b. isomerizes all-trans-retinal to 11-cis-retinol

c. does not undergo mitosis in response to injury

d. secrets the outer layer of the basal lamina that forms the Bruch's membrane.

e. has multiple apical villi into which the outer segment of the photoreceptor 
    outer segments are embedded.

answera.F   b.T   c.F   d.F   e.T
Vitamin A in RPE is stored in ester form and therefore less toxic to the cells. Only the inner layer of the basal lamina is secreted by the RPE
 
 

2. The following are found in higher concentration in the tear than in the serum:

a. sodium

b. potassium

c. Ig G

d. glucose

e. chloride

answera.F   b.T   c.F   d.F   e.T
Sodium in tear is the same concentration as those in the serum but the chloride and potassium are much higher.  Serum Ig G is higher than that in the tear.
 
 

3. The corneal stroma:

a. measures 500 um thick

b. transmits 90% of the incoming light

c. derives most of its oxygen from the precorneal tear film

d. is acellular which accounts for its transparency

e. contains collagen fibrils which forms obliquely oriented lamellae in the 
    posterior third of the cornea

answera.T   b.F   d.F   d.F   e.F
It transmits 98% of the light.
The oxygen is derived mainly from the aqueous.
The stroma contains keratocytes which are important in the repair of stroma.
In the anterior third, the collagen fibrils forms obliquely oriented lamellae and in the posterior two-third they are parallel.

p
4. The following proteins found in the tear of a normal person have antibacterial activity:

a. lysozyme

b. lymphokines

c. betalysin

d. immunoglobulin M

e. lactoferrin

answera.T   b.F   c.T   d.F   e.T
Lymphokines and immunoglobulin M are not normally found in the tear of normal person. The four main proteins found in the tear with antibacterial activities are lysozyme, betalysin, Ig A and lactoferrin.

y
5. The following are true about electro-retinography?

a. flicker ERG can be used to test cone function

b. ERG is normal in patient with macular degeneration

c. the a-wave of ERG is produced by the ganglion cells

d. the b-wave is produced by the photoreceptor cells

e. c-wave is produced by the RPE cells

answera.T   b.T   c.F   d.F   e.T
Flicker ERG can be used to test cone function as rods do not respond to flashes with greater 15Hz frequencies.
The a-wave is produced by the photoreceptor cells and the b-wave by the bipolar and Muller's cells.

 
 

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