Test 172 (modified from MRCOphth Questions, 2003)

1. The following are true about cones: 

a. they are taller and thinner in fovea 

b. they are absent in the optic disc

c. 90% of the cones in the retina is situated outside 
    the central 5 degrees of the macula

d. the red and green pigments are encoded on the 
    long arm of X chromosome

e. the chromophore of each cone pigment exists as 
    11-trans-retinal
 

Answera.T   b.T  c.T   d.T  e.F
The cones are found throughout the retina but has 
the highest density in the fovea or central 5 degrees. However, 90% of the cone population is outside the fovea. The chromophore of each cone likes that of rod exists as 11-cis-retinal.

2. Myelin of the nerves is produced by:

a. fibroblast

b. macrophage

c. Schwann cell

d. oligodendrocyte

e. Müller cells
 

Answera.F  b.F  c.T  d.T  e.F
Myelin of the peripheral nerve is produced by Schwann cells whereas that of the central nervous system is produced by oligodendrocytes.
 
 

3. The following are true about human chromosomes:

a. chromosome 21 is bigger than chromosome 22

b. X chromosome is bigger than Y chromosome

c. the p arm of a chromosome is bigger than the q arm

d. acrocentric chromosome has very small short arm

e. 13q14 deletion means that band 13 on the long arm 
    of chromosome 14 is deleted.
 

Answer
a.F   b.T  c.F  d.T  e.F
The autosomes are numbered according to their sizes with the exception of chromosome 21 and 22. 
Chromosome 22 is bigger than chromosome 21.
p stands for 'petit' meaning small. 13q14 deletion means deletion of band 14 on the long arm of chromosome 13 ie. occurring in some forms of retinoblastoma.

 

. 4. The following antibiotics are useful for treating chlamydial
      infection:

a. tetracycline

b. penicillin

c. sulphonamide

d. erythromycin

e. metronidazole
 

Answer
a.F  b.F  c.T  d.F  e.T
Erythromycin and the tetracycline block chlamydial protein synthesis by inhibition of the 50S and 30S ribosomal subunits, respectively. The other antibiotics are ineffective.

5. The retinal pigment epithelium:

a. contains both tight and gap junction

b. contains melanin on its apical surface

c. produces c wave of the ERG (electroretinogram)

d. produces part of the Bruch membrane

e. is not permeable to sodium fluorescein molecules
 

Answer
a.T   b.T  c.T  d.T  e.T
A continuous series of tight junctions encircle the cells and forms the blood retina barrier between the choriocapillaris and the retina. Adjacent RPE cells are also joined by gap junctions that electrically couple the cells together.

 

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