Test 199  (Ocular physiology)

1. The following are true:

a. a horopter is a straight line on which an object will 
    stimulate corresponding retinal points

b. objects further or nearer than the horopter to the eyes 
    are always perceived as double

c. objects in the Panum's area are perceived singly

d. objects outside the Panum's are are perceived as 
    double

e. the Panum's area is wider centrally than peripherally

 
Answera.F   b.F  c.T   d.T  e.F
The horopter is a curve. Objects further or nearer than 
the horopter to the eyes can still be perceived singly if they are in the Panum's area. The Panum's area is narrower centrally than in the periphery.

2. Doll's head phenomenon:

a. refers to movement of the eyes in a direction opposite 
    to which the head is suddenly moved

b. elicits both horizontal and vertical vestibuloocular 
    reflexes 

c. is absent in patients with brain stem death

d. is impaired in patients with severe bilateral vestibular 
    deficits

e. can not be elicited in patients with bilateral cortical 
    blindness

 

Answera.T  b.T  c.T  d.T  e.F
Doll's head phenomenon is intact in patients with cortical blindness. It is a brain stem response and used to elicit both horizontal and vertical vestibuloocular reflexes.

 

3. The following are true about ocular circulation:

a. only 4% of the total blood supply to the eye goes to 
    the retina

b. the choroidal blood flow in normal people is ten times 
    that of the grey mater of the brain

c. autoregulation occurs in both retinal and choroidal 
    circulation

d.  a PaCO2 rise of 1 mm Hg induces a 3% rise in retinal 
     blood flow

e. hypoxia causes dilatation of the retinal blood vessels

 
Answer
a.T   b.T  c.F  d.T e.T
85 out of 100% of the total blood supply to the eye
is distributed to the choroid and only 4% to the retina. 
From the remaining 11%, 10% is distributed to the ciliary body and 1% to the iris. Autoregulation is present in the retinal blood vessels but not in the choroidal blood vessels.

 

. 4. The following may explain why a patient who had had a relative
      afferent pupillary defect has normal pupillary reaction to light:

a. removal of a cataract

b. resolution of optic neuritis

c. anterior ischaemic optic neuropathy in both eyes

d. development of bilateral papilloedema

e. instillation of cyclopentolate into the affected eye

Answer
a.F  b.T  c.T  d.F  e.F
A patient with a definite relative afferent pupillary defect
in one eye on the first visit but returning for follow-up and show no relative afferent pupillary defect may indicate one of two things:
a. an improvement in the previously damaged eye. 
b. there is now damage in what was previously the better eye, matching the damage to the other eye

5. In efferent pupillary defect:

a. anisocoria is present

b. the damage may be in the visual cortex

c. the damage may be in the superior colliculus

d. the lesion may be in the ciliary ganglion

e. damage to the iris dilator muscle is a cause

 
Answer
a.T   b.T  c.T  d.T  e.T
Unlike afferent pupillary defect, in efferent pupillary defect anisocoria is present. These are seen in disorders that interfere with the contraction or dilatation of the pupil. The location of damage affecting the pupillary 
response to light, dark, or near may be in the midbrain, along the course of the peripheral nerves supplying the iris dilator or sphincter muscle, or directly in the iris tissue itself. 

 

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