KERATOMETER MEASURING TECHNIQUE

The keratometer measures the curvature 
of the cornea by reflecting mires 
(images) from the cornea and takes 
readings from two points on the corneal 
surface using a doubling technique (see 
How the Keratometer Works ).  Since the 
measurement is made from just these 
two small points, the keratometer only 
gives an approximation of the central 
curvature and does not give information 
about the whole surface. 

The separation of the two points 
on the cornea will vary with the 
corneal curvature.  For the 
average corneal curvature the 
separation is about 3.2 mm.