The two patients above are undergoing two different electrophysiology tests.

a. What electrophysiology is performed in A?

b. What electrophysiology test is performed in B?

c. Suggest one ocular condition each that may be detected with A and B 
    before the onset of symptoms and signs.

a
Answer a
ERG (electroretinogram). A contact lens is used in this test.
 

Answer b
EOG (electrooculogram).
 

Answer c
ERG can be used to detect retinitis pigmentosa before the onset of signs and symptoms and EOG for early stage of Best's disease.