When light rays enter the eye, most of the refraction occurs at the 

A student sitting at the back of the classroom cannot read clearly the letters written on the blackboard. What advice will a doctor give to her? Draw ray diagram for the correction of this defect.

A person needs a lens of power $-4.5 \mathrm{D}$ for correction of her vision. What kind of defect in vision is she suffering from?

A person needs a lens of power $-4.5 \mathrm{D}$ for correction of her vision. What is the focal length of the corrective lens?