Referring to the picture above.

a. What is the name of this instrument?

b. Is the axial length measured with this instrument longer
    or shorter than the conventional ultrasound biometry.

c. Name three advantages of this instrument over
    ultrasound biometry.

 
Answer a
Laser interferometric biometry. It is used to measure axial length based on the principle of partial coherence interferometry. 
 

Answer b
Longer than ultrasound biometry.
Two reasons for this:
a. it is non-applating.
b. it measures up to the pigment epithelium unlike ultrasound that measures to the inner limiting membrane. 

 

Answer c
Advantages are:
better comfort for the patient.
no need for local anaesthesia 
minimized risk of corneal infection 
better precision 
better resolution
less dependent on the experience of user.