I

II

The ERGs above are elicited with full-field white 30-Hz flashes. Patient I is a normal subject and patient II has ocular problem.

a. What are responsible for the negative and positive 
    deflections?

b. Suggest a possible cause for the tracing in patient II.

 

Answer to a
The negative 'a' wave is due to repolarization of 
the photoreceptors and a positive 'b' wave arising from the bipolar cells.
 

Answer to bRetinitis pigmentosa. 
In patient II, the tracing shows reduced amplitude and 
is seen in a variety of retina conditions such as retinitis 
pigmentosa. As the disease progresses, the tracing eventually becomes flat.