Test 195  (Ocular anatomy)

1. The optic nerve:

a. contains no neuronal cell bodies

b. contains no interneurones

c. contains microglial cells which act as resident 
    macrophages

d. contains astrocytes that regulate extracellular potassium

e. contains oligodendrocytes that are responsible for 
    axonal myelination

 
Answera.T   b.T  c.T   d.T  e.T

2. The following are true about the optic chiasm:

a. axons nasal to the optic disc decussate at the chiasm

b. in normal population 47% of the optic nerve fibres 
    decussate at the chiasm

c. decussation of the optic nerve fibres is increased in 
    albinism

d. it is situated beneath the third ventricle

e. a post-fixed optic chiasm is one in which the pituitary 
    gland is anterior to it

 

Answera.F  b.F  c.T  d.T  e.T
Axons nasal to the fovea decussate at the chiasm. About 53% of the optic nerve decussate at the chiasm. The decussation increases in albinism.

 
 

3. The muscle of Riolan:
 

a. is a smooth muscle

b. is the most posteriorly placed orbicularis oculi along 
    the eyelid margin

c. courses the length of the eyelid

d. represents the gray line seen clinically

e. contracts during blinking and shorten the canaliculus 

 
Answer
a.F   b.T  c.T  d.T  e.T
Striated muscle fibres adjacent to the tarsal plate are
known as Riolan 's muscle. It is the posteriorly placed 
orbicularis oculi along the eyelid margin. It together with the pretarsal orbicularis oculi surround the canaliculus and during blinking, they contract and shorten the canaliculus forcing the tear into the lacrimal sac.

 

. 4. The meibomian gland:

a. drains into a central ductule that opens in the 
    mucocutaneous junction

b. secretion increases with age

c. secretes a mixture of lipids that has a melting point of
    35⁰C

d. production is increased with application of topical 
    androgen

e. dysfunction is best measured with Schirmer's test

Answer
a.T  b.T  c.T  d.T  e.F
Unless sebaceous gland in other parts of the body.
The secretion of meibomian gland increases with age. 
Schirmer's test measures mainly the amount of aqueous component of the tear.

5. The inner plexiform layer contains the following cells:

a. photoreceptors

b. Müller cells

c. ganglion cells

d. bipolar cells

e. amacrine cells

 
Answer
a.F   b.T  c.T  d.T  e.T
Inner plexiform layer (IPL) contains bipolar, amacrine, and ganglion cells synapse which synapse with one 
another. Müller cells extend through the whole thickness of the retina.

 

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