Test 56  (Ocular physiology)

1. The Pulfrich phenomenon:

a. occurs in patients with bilateral macular degeneration

b. occurs in optic neuritis

c. refers to the perception of photopsia 

d. refers to the illusion of abnormal motion

e. can occur with a swinging pendulum

Answer
a.F    b.T   c..F   e.T   e.T
Pulfrich phenomenon refers to the illusion of abnormal motion .
It occurs in unilateral optic neuritis.
It can be illustrated with a swinging pendulum. In patients with optic nerve abnormalities,  the pendulum which swings in a straight line is perceived as if it were in an elliptical pattern. 

2. The following are true about the contrast sensitivity:

a. Pelli-Robson chart tests the contrast sensitivity

b. is a measure of the ratio of brightness to darkness

c. a contrast of 1 means that there is no contrast

d. is highest at middle range frequencies

e. is reduced in macular degeneration but not in cataract

Answer
a.T   b.T   c.F   d.T   e.F
Contrast sensitivity refers to a person's ability to see differences in contrast across different spatial frequencies.
It is measured with Pelli-Robson chart and Vistech wall chart.
It is highest at the middle range frequencies.
A contrast of 1 means white on black whereas 0 means there is no contrast.
It is reduced in cataract as well as macular degeneration.
 

3. The following are true:

a. depth of perception only occurs in patients with 
    normal visual acuities in both eye

b. Hering's law states that increased innervation to an 
    extraocular muscle is accompanied by a decrease 
    in innervation to its antagonists. 

c. objects on the Panum's area fall on simultaneous 
    areas of the retina

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

e. objects on the horopter are seen as single

Answera.F   b.F   c.F   d.T   e.T
Hering's law states that equal and simultaneous innervation flows to muscles that act in the same direction of gaze ie. syngergists.
Objects on the Panum's area fall on disparate areas of the retina

4. The following are yoke muscles:

a. right medial rectus and left lateral rectus

b. right inferior rectus and left superior rectus

c. right superior rectus and left inferior oblique

d. right superior oblique and left inferior rectus

e. right inferior rectus and left inferior oblique

Answera.T   b.F   c.T   d.T   e.F
Yoke muscles refer to two muscles one in each eye which when contract move the eyes to a certain position.
Therefore the correct pairing should be:
right inferior rectus and left superior oblique
right inferior rectus and left superior oblique

5. The following are true about fluorescein sodium:

a. it is 60% bound to the plasma protein

b. it  leaks out of the choriocapillaris readily

c. is excreted mainly by the kidney

d. it is excited by green light

e. it has a emission peak of 530nm

Answera.F   b.T   c.T   d.F   e.T
It is 85% bound to the serum protein.
The choriocapillaris is fenestrated and therefore fluorescein leaks out of it readily.
It is excited by blue light.
The excitation peak is 490nm and emission peak is 530nm.