ABSTRACT
The Zeiss IOLMaster is a noncontact optical device that measures axial length of the eye by partial coherence interferometry, with a consistent accuracy of 0.02 mm (less than 0.10 diopter), or better. It also does automated keratometry, measures anterior chamber depth, the horizontal corneal diameter, and calculates intraocular lens powers, all in a single sitting.1-6
The IOLMaster employs a modified Michelson interferometer to divide, and phase delay, a 780 nm partially coherent beam of light. One beam is reflected from the corneal surface, while the other is reflected from the retinal pigment epithelium. A photodetector and on-board computer translate the interference pattern produced by the two beams into a highly accurate measurement of axial length. Calibrated against the ultra-high resolution 40-MHz Greishaber Biometric System, an internal algorithm then approximates the distance to the vitreo-retinal interface, for the equivalent of the ultrasonic axial length. Considering the fact that axial length measurements by A-scan ultrasonography (using a standard 10-MHz transducer) have a typical resolution of 0.10 mm to 0.12 mm, axial length measurements by the IOLMaster represent a fivefold increase in accuracy.
