Carl Zeiss Meditec IOL Master
Cataract Surgery Arizona

IOLMaster — Keratometer Measurements.

IOLMaster Arizona   IMPORTANT: Now and then, there are reports on different K readings on the IOL Master as compared to other keratometers. Also, discrepancies in IOL powers are reported comparing IOL Master results with those obtained on ultrasound equipment, even when the same input data was used.

Very often, the described problems can be traced down to keratometer indices and/or to peculiarities of corneal power implementations in the IOL formulas of the respective instruments.


Measurement of Corneal Curvature (KER)

1. Activate Keratometer Measurement Mode:

  • clicking on the KER icon
  • pressing the <K> key
  • pressing the <SPACE BAR> in ALM mode (ALM)

2. Tell the patient to focus on the yellow light Cataract Surgery Arizona.

3. Align the IOLMaster.

The 6 peripheral measuring points should be symmetrical to the circular cross-hair and appear optimally focused. The central point is usually not focused and is not evaluated for keratometer measurement. The IOLMaster with Advanced Technology indicates the optimum measurement setting by means of a green traffic light.

IOLMaster Arizona   Note
Ensure that all 6 peripheral points are visible and located in the field between the two auxiliary circles on the display. It is recommended that the patient blink his/her eye shortly before the measurement to produce a continuous tear film. This will improve the reflectivity of the cornea. The measuring points should be circular or ellipsoid. If the measuring points are irregular (i.e. corneal scar), measurement is not possible. Precise measurements are possible only if the 6 peripheral measuring points appear optimally focused on the display.
  IOLMaster Keratometer

4. Take the measurement by pressing the button on the joystick.

Depending on the setting under Program settings/Program, a traffic light will assist in finding the optimum measurement setting. When the optimum measurement position has been reached, the traffic light will change from red to yellow to green. Once the optimum measurement setting (green traffic light) has been reached and remains constant for all three measurements, pressing the knob on the joystick in Automatic mode (Automatic activated) will trigger three consecutive measurements. The automatic measurement procedure will be interrupted if the optimum measurement setting (green light) wavers and is resumed when the optimum setting is reinstated.

Five internal individual measurements are taken for a single keratometer measurement within 0.5 seconds. Following this, the radii or corneal K’s (depending on program settings) of the two main sections will be displayed, together with the respective axial orientation and the astigmatic difference. In the case of a spherical cornea, only the radius or a corneal K will be displayed, but no axial orientation or astigmatic difference. A blue progress bar in the status bar will indicate the progress of computation.

IOLMaster Keratometer  

The size and shape of measurement points are verified by the software. If a measurement point is not correctly identified, a blue flashing dot will appear. In the printout this will be marked by an x. These readings should not be used and a new measurement should be taken as a precaution.

Keratometer measurements may be repeated as often as desired; however, only the last three measurements will be displayed.

IOLMaster Arizona   Note
The number of measurements is crucial here. The IOLMaster requires THREE keratometer measurements to be taken! The message Measure again will thus appear. Only then will a mean value be passed on to the IOL calculation and an evaluation enabled.

IOLMaster Arizona   Note
In some cases (keratoconus, keratoglobus, corneal lesions, etc.) it may not be possible to reach the green traffic light. In such cases the traffic light display can be briefly deactivated, enabling a measurement to be taken even when the light is on yellow or red. To do this, press the <M> key. The Automatic display will disappear. However, now pay attention to the correct setting, as described above. Press the <M> key once again to reactivate automatic. Automatic will always be switched back on for a new patient.

IOLMaster Keratometer


To delete one of the three displayed readings, select it and press the <DEL> key. Now confirm with YES.

If the last three readings differ by > 0.5 D (mean value of the spherical equivalent of the last three measurements) or if the tolerance of the mean radius of the last three readings of 0.08 to 0.1 is exceeded (dependent on n), the Evaluation! message will appear on the screen.

  • In this case, check the tear film of the eye being examined, ask the patient to blink if necessary and repeat the measurements until the results are within the tolerances. The Evaluation! message will then disappear.
  • Potential measuring errors (inaccurate measurements) must be deleted as necessary, since the readings obtained in the Evaluation! state will not be accepted for ACD measurement, IOL calculation and the database for optimization of constants.
IOL Master warning WARNING: To obtain consistent results check the individual keratometer measurements and carry out further measurements if necessary.

The following plausibility tests will be made with the keratometer reading:

  • R > 8.4 mm Cataract Surgery Arizona Possible flat corneal curvature, keratoglobus
  • R < 7.2 mm Cataract Surgery Arizona Very steep corneal curvature
  • R < 7.0 mm Cataract Surgery Arizona Possible keratoconus
  • |R1 - R2| > 0.5 mm Cataract Surgery Arizona High astigmatism

When both eyes have been measured, the difference in the keratometer readings between the right and left eye will be checked. If this exceeds 0.2 mm or 1 D, you will be prompted to check the readings once again.

If this warning appears, be sure to verify that no pathological changes have occurred in the eye. It may be necessary to repeat the measurements. Only confirm the warning with OK if you are certain that the readings are plausible. Otherwise, determine what has caused the implausible readings. A reference to the displayed plausibility test message will be transferred to the comments box.


Be sure to read: Tips for Keratometer


Be sure to read: Tips for Keratometer