Improved refractive targeting can be achieved by optimising IOL A-constants for optical biometry. As formulae for IOL power calculations have been tested with A-scan AL measurements, targets of –0.3 D to –0.5 D are recommended to achieve emmetropia when using optical biometry. AL readings are typically 0.1 mm longer with the IOLMASTER compared to A-scan. A trace with a signal-to-noise ratio (SNR) of ≥2.0 is acceptable however, the higher the SNR, the more accurate the reading. Optical interferometery: noncontact and measures AL to the RPE (rather than the vitreo-retinal interface as in ultrasound).
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