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A TEXTBOOK OF PHYSIOLOGY 



about 6 metres away, and endeavours to read the types. Defective 

 vision is usually recorded by stating the distance from the type as 

 numerator, and the distance at which the last line read by the subject 

 should normally be read as the denominator. Normal vision (V) 



FIG. 307. THE PEKIMETKR. 



is that is, the 6-metre type can be read at 6 metres. V=/ ff 

 signifies that at 6 metres' distance the subject only succeeded in 

 reading type which should normally be read at 36 metres. 



It is customary to employ an instrument called a perimeter to 

 obtain accurate details of the extent of the field of vision. The 



