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

1/1/2005 Chapter 8 Corneal Curvature and Topography page 8-2
(1) Attach the steel ball holder (Lensco-meter) to the upright support of the
forehead rest, at approximately the canthus mark, if present. Angle the steel ball holder
toward the barrel of the instrument so that the steel calibration ball is approximately at
the plane that the eye would be during routine keratometry.
(2) Take a reading from each steel ball (40.50 D, 42.50 D, and 44.75 D) in both the
vertical and horizontal meridians.
(3) If the keratometer is more than 0.25 D out of calibration, recalibrate the
keratometer by adjusting the measuring wheels. This is accomplished by loosening the
two set screws and rotating the wheels into the appropriate positions.
8.2.3 Keratometry Measurement Procedure
Keratometry is performed at each CLEK Study Visit as follows:
(1) Ask the patient to place his/her chin in the chin rest and forehead against the
headrest.
(2) With the keratometer in the straight ahead position, sight down the outside of
the instrument and adjust the instrument vertically until the leveling sight is aligned
with the patient’s temporal canthus.
(3) Occlude the eye not being tested. Release the knob for locking the instrument
and rotate the instrument until it points directly at the eye to be tested. Instruct the
patient to look into the instrument where he/she may see a reflection of his/her own
eye.
(4) Adjust the focus of the instrument until the image of the mires is clear.
(5) Make fine vertical and horizontal adjustments necessary to place the reticule
cross near the center of the lower right mire image.
(6) Rotate the instrument (to locate the horizontal or near horizontal principal
meridian) until the horizontal bars of the two crosses to the left of the focusing mire are
aligned. Maintain clarity of the image during this step by continual refinement of the
focus.
(7) Turn the horizontal measuring knob (on the left of the instrument) until these
two crosses are superimposed.