In September 1999, the first automated non-invasive optical biometry device became available for clinicians – the IOLMaster from Carl Zeiss Meditec. The ZEISS IOLMaster operates as a modified Michelson interferometer and uses infrared laser light (wavelength 780 nm) to provide repeatable and precise measurements of the AL,4 curvature of the anterior corneal surface,5 ACD,6 and the horizontal visible iris diameter (white-to-white diameter, WTW).7
The technique underlying ZEISS IOLMaster biometry is partial coherence interferometry: A signal is produced as a result of the interference between the light reflected by the tear film and that reflected by the retinal pigmentary epithelium. Several studies comparing the ZEISS IOLMaster device to contact and/or ultrasonographic techniques have demonstrated repeatability and accuracy of measurements (Connors et al 2002, Sheng et al 2004).8 9
One reason for this accuracy is the reduced dependence of the biometric measurement on the examiner's experience, as only the alignment of the device to the patient´s eye is required while the rest of the process is automated.
The only limitation of optical biometers has been the inability to measure AL and ACD in eyes with densely opacified media. In the ZEISS IOLMaster 500 this can be overcome by connecting it to an ultrasound probe that can provide AL measurements in those eyes with very dense corneal leukomas and/or cataracts.10 Additionally, other values can be entered manually. Thus, almost any type of eye can be measured with this combined technology. Moreover, with the newly available ZEISS IOLMaster 700, featuring SWEPT Source OCT measurement, it has been shown that necessary ultrasound cases could be reduced by 92%, achieving a cataract penetration rate of 99%. 11
Accurate biometry measurements and IOL calculations can be performed quickly and easily.