A doctor who recently began his ophthalmic training was trained to perform A scan for patient's biometry. An audit
performed on his biometry showed that 70% of the patients had a post-operative refraction of >-1.00DS of spherical equivalent from what the surgeons intended. 

a. What is the most likely reason for his error during A-scanning?

b. Name two methods which may be used to improve the biometry results. 

 
Answer a
Under-estimating the axial length due to indentation of the cornea.

Indentation of the cornea gives an axial length which is shorter than

expected. The post-operative refraction will be more myopic than expected.
 

Answer b
Immersion technique for the A scan or
Partial coherence interferometry.