OM t of c.iii - Vision Research Coordinating Center - Washington ...

1/1/2005 Chapter 8 Corneal Curvature and Topography page 8-3
(8) The orientation of the keratometer drum may have to be changed to align the
mires for the vertical meridian. This represents irregular astigmatism, ie, the two
principal meridians are not oriented exactly 90° apart, and they should be recorded as
they appear on the keratometer.
(9) Direct your attention to the two horizontal lines above the focusing mire and
turn the vertical measuring knob (on the right of the instrument) until these lines are
superimposed.
(10) Record the dioptric value of the flatter and steeper curvatures to the nearest
0.12 D, and the meridians of each curvature as indicated on the instrument scale.
(11) Move the vertical and horizontal measuring knobs away from the final
measurement, and repeat steps 7-9 on the right eye and record a second set of
keratometric readings.
(12) Repeat procedure steps 1 through 10 for the left eye.
8.2.4 Extending the Keratometer’s Range
If the patient’s cornea is steeper than 52.00 D (i.e., off the scale) in either
meridian, the range of the keratometer will need to be extended as follows:
(1) Insert the supplied +1.25 D lens to the keratometer target (objective side).
(2) Table 8-1 should be consulted to convert the readings with the +1.25 D lens in
place to actual readings.
(3) If the patient’s cornea is off the scale of the keratometer in either meridian
with the +1.25 D lens in place, steps 1-2 above should be repeated with the +2.25 D lens
in place, consulting Table 8-2 for the conversion of the drum reading to the actual
reading.
(4) If the patient’s cornea is off the scale of the keratometer in either meridian
with the +2.25 D lens in place, record the keratometric meridian in that meridian as “>
68.30,” inserting the “>“ sign just to the left of the keratometry reading boxes on the
CLEK Examination Form.