Test 189  (Ocular physiology)

1. The bright-flash ERG:

a. comes only from the cones

b. is generated in a fully dark adapted eye by the highest 
    intensity of light

c. can be used to assess the overall retinal integrity in 
    the presence of media opacity

d. is abnormal in patients with age-related macular 
    degeneration

e. is abnormal in optic neuritis.

 
Answera.F   b.T  c.T   d.F  e.F
Bright-flash ERG refers to the ERG response generated in the fully dark adapted eye by the highest intensity light. It is a summation of all rods and cones and gives an indication of overall retinal integrity. It may be of use when the media is so opaque that the retina is not visible (e.g., cataract). The caveat to keep in mind is that while the response may be normal it does not give any information regarding the state of the macula or the optic nerve.

2. The following cells contribute the wavefronts of the flash ERG:

a. retinal pigment epithelium

b. corneal endothelium

c. photoreceptors

d. ganglion cells

e. Müller cells

 

Answera.T  b.F  c.T  d.F  e.T
In flash ERG, the a wave comes from the photoreceptors, b wave from the Müller cells and c wave from the retinal pigment epithelium.

 
 

3. The parameters that are measured clinically in the flash ERG are:
 

a. amplitude

b. excitation time

c. implicit time

d. latency

e. Arden index

 
Answer
a.T   b.F  c.T  d.F  e.F
The two parameters of the ERG that are measured clinically are the amplitude (measured in microvolts, µV) and the implicit time (measured from the onset of the stimulus to the peak of the response in milliseconds). 

 

. 4. The following methods can be used to test solely the rod ERG:

a. a rapidly flickering light

b. red light stimulus

c. low-density blue light in dark adapted eye

d. focal ERG

e. pattern ERG

Answer
a.F  b.F  c.T  d.F  e.F
The rods can not respond to a rapidly flickering light. 
The rods are very sensitive to light from the blue end 
of the spectrum, while the cones are quite insensitive
to this short wavelength light. Thus in a dark-adapted eye, if a low-intensity blue light is used as the stimulus, the resultant response will be indicative of rod function.

5. Pattern ERG (PERG):

a. tests the function of the ganglion cells

b. uses a checkeredboard pattern that changes in luminance

c. gives the same information as visual evoked response
    (VER)

d. is abnormal in glaucoma

e. is affected if the patient's refractive error is not 
    corrected

 
Answer
a.T   b.F  c.T  d.T  e.T
pattern ERG provides a response which is derived from ganglion cells. Using a checkerboard pattern which changes from black-to-white, but does not change in luminance, the luminance change needed to elicit a standard ERG is thus eliminated. This type of ERG gives the same information as VER.
Diseases that affect the ganglion cells such as glaucoma or optic neuritis will give rise to abnormal pattern ERG.

 

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