Test 72     (Ocular physiology)

1. During accommodation:

a. the distance between the lens and the ciliary body is 
    decreased
b. the tension in the suspensory ligament is increased
c. the tension of the lens capsule is increased
d. the refractive power of the lens is increased
e. there is an increased sympathetic outflow to the ciliary
     muscle

Answera.T   b.F  c.F   d.T   e.F
During accommodation:
the tension in the suspensory ligament is reduced.
the tension of the lens capsule is decreased
there is an increased parasympathetic outflow to the ciliary muscle.

2. True statements about accommodation:

a. it does not occur in the absence of convergence
b. it occurs equally in both eyes
c. the range of accommodation decreases with age
d. the amplitude of accommodation is about 30D at birth
e. it is impaired by phenylephrine

Answera.F  b.T   c.T   d.F   e.F
Although accommodation is accompanied by convergence and pupil constriction. It can occur in the absence of convergence.
The amplitude of accommodation in the new born is about 14D.
Phenylephrine is a mydriatic but not a cycloplegic, therefore accommodation is not impaired.

3. The visual acuity is affected by:

a. pupil size
b. illumination of the target
c. red-green colour blindness
d. contrast
e. posterior subcapsular cataract more than anterior 
    subcapsular cataract

Answera.T   b.T   c.F   d.T   e.T
A smaller pupil size reduces chromatic and spherical aberration. 

4. The following are true about pupillary reaction to light:

a. it is impaired in damage of the Edinger-Westphal 
    nucleus
b. it is impaired in damage of the ciliary ganglion
c. it is impaired in damage of the superior cervical ganglion
d. the pupil does not respond to light with a frequency of 
    greater than 5 Hz
e. the latent period for pupillary reaction to light is shorter 
    than that for accommodation.

Answera.T   b.T   c.F   d.T   e.T
Pupillary reaction to light is controlled by the parasympathetic nervous system. Therefore damage to the superior cervical ganglion (as in Horner's syndrome) does not impair the pupillary reaction.
The latent period for pupillary reaction to light is between 0.2 to 0.5s shorter than that for accommodation.

5. The following are true:

a. heroin causes miosis by increasing the release of 
    acetylcholine.
b. botulinum toxin causes mydriasis by inhibiting the 
    release of acetylcholine
c. phenylephrine causes mydriasis by stimulating the 
    a receptors
d. amphetamine causes mydriasis by inhibiting 
    noradrenaline reuptake
e. carbachol causes miosis by increasing the release of 
    acetylcholine

Answera.F   b.T   c.T   d.F   e.T
Heroin causes miosis by removing the cortical inhibition of Edinger-Westphal nucleus.
Amphetamine causes mydriasis by increasing the release of noradrenaline from the nerve pre-synaptic neurones.

 
 

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