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Measuring a Cataract of Mild to Moderate Density

In measuring a cataract of mild to moderate density, the IOL Master axial length display should show the above characteristics. However, with increasing cataract density, and decreasing signal-to-noise ratio, the secondary maxima often disappear into the baseline. As long as the primary maxima is narrow, and has a well-defined and centered terminal peak, the measurement is considered valid.

If the signal-to-noise ratio of the eye to be measured is borderline (2.0 to 1.6), focusing in, or focusing out, in such a way that that focusing spot enlarges to about the same size as the measurement reticule, will sometimes significantly improve the quality of the axial length display. This is possible with the IOL Master because axial length measurements by partial coherence interferometry are distance independent.

Remember to use the Best Measurement Technique and sample several areas around the center of the measurement reticule until the best display is obtained. The important components of accuracy with the IOL Master are: correct alignment with the fixation light, measurement consistency, and a correct display pattern. Experience has shown that this general rule applies to signal-to-noise ratios as low as 1.6.