Test 188  (Ocular physiology)

1. The Bell's phenomenon:

a. occurs during normal blinking

b. if absent suggests brain stem disease

c. is absent in Bell's palsy

d. causes the globe to rotate 45⁰ above the horizontal

e. is reduced or absent in patients with thyroid orbitopathy

 
Answera.F   b.F  c.F   d.F  e.T
The Bell's phenomenon occurs during forced eyelid closure in which the globe rotates about 15 degrees above the horizontal. It is absent in 10% of the population. In restrictive orbitopathy such as thyroid eye disease, it is reduced.

2. The following are true about pupil reaction to light:

a. secretion of acetylcholine is responsible for pupil 
    dilatation

b. constriction of the pupil is mediated by nerve fibres 
    travelling in the short ciliary nerve

c. dilatation of the pupil is mediated by nerve fibres 
    travelling in the long ciliary nerve

d. the sympathetic nerve innervates the dilator muscles

e. the sympathetic nerve supply to the iris travels through 
    the cavernous sinus

 

Answera.F  b.T  c.T  d.T  e.T
Secretion of acetylcholine at the post-ganglionic parasympathetic nerve fibres causes miosis.

 
 

3. The following are true about the vestibuloocular reflex:
 

a. it receives input from the semi-circular canal

b. it receives input from the otolith

c. it is suppressed when the object is moving with 
    the subject

d. it keeps the image stable on the retina

e. is impaired in lesion of the medial longitudinal fasciculus

 
Answer
a.T   b.T  c.T  d.T  e.T

 

. 4. The human lens:

a. is innervated by the ophthalmic nerve

b. has a uniform refractive index

c. has a large radius of curvature anteriorly than posteriorly

d. stops growing after birth

e. derives its energy chiefly from anaerobic glycolysis

Answer
a.F  b.F  c.T  d.F  e.T
The lens has no sensory innervation. The cortex and the nucleus have difference refractive indexes. The lens continues to grow throughout life. 80% of the lens glucose is metabolized by anaerobic glycolysis.

5. The following are true about the ERG:

a. in infarction of the choroidal circulation the a-wave 
    of the ERG is reduced or absent

b. the ERG is always abnormal in patients with macular 
    diseases

c. flicker ERG can be used to isolate cone photoreceptors

d. the b-wave of ERG is reduced in dark-adapted eye

e. the ERG is abnormal in patients with glaucoma

 
Answer
a.T   b.F  c.T  d.T  e.F
The a-wave is produced by photoreceptors supplied by the choroidal circulation. Patter ERG but not the normal ERG is abnormal in macular disease. The rods do not respond to high flash frequencies and therefore flicker ERG can be used to isolate cones. The ERG is not affected in glaucoma as the ganglion cells and the optic nerve do not contribute to the ERG wavefronts.

 

More MCQs