KERATOMETER MEASURING TECHNIQUE

Making the Power Measurement

Once the horizontal lines of the plus signs are 
aligned, rotate the horizontal power drum (on 
left side) until the vertical lines of the plus signs 
are overlapping.  Next rotate the vertical power 
drum (right side) until the minus signs overlap.  
Be sure to overlap the mires as accurately as 
possible.  It is often necessary to refocus the 
mires during the measurement and between 
reading the horizontal and vertical meridians.

                                                                                                    If the drum(s) are rotated 
                                                  to their full extent and 
                                                  the mires still do not align
                                                  (the cornea is steeper or  
                                                   flatter than the range  
                                                   of the instrument), the                       
                                                   range of the instrument 
                                                   must be extended.