You examine the fundi of a patient's retina with an indirect ophthalmoscope using first a 20D and then a 28D. With either lens, the optic disc increases in size as you move the lens away from the patient's eye.

a. What are the differences in the image size and field of vision between 20D and 28D?

b. What is the refractive status of this patient?

 

Answer to a
20D lens gives a higher angular magnification than 28D (2.97X vs 2.16X). 
A 20D lens has a smaller field of vision than 28D (26 degrees vs 55 degrees).
 

Answer to b
Myopia. 
With indirect ophthalmoscope, the image size is the same irrespective 
of the position of the lens if the patient is emmetropia. If the patient is myopia,
the image increases in size as the lens is moved away from the eye but decreases 
as the lens is moved closer. The reverse is true for hypermetropia.