Precise biometry is essential for accurate outcomes in cataract and refractive surgeries. The measurement of axial length by ultrasound was the gold standard for many years. With the introduction of optical biometry in the United States in the year 2000, this technology has become more and more popular and is now the most common method for the measurement of axial length. Optical biometry presents an accurate alternative for precise ocular measurements, used not only for axial length, but anterior chamber depth, lens thickness, pachymetry and retinal thickness measurements.
Haag Streit LENSTAR®
Carl Zeiss Meditec IOLMaster®
Optical biometry uses a partially coherent wave that has approximately 9x the resolution of a 10 MHz sound wave, making the measurement of axial length very precise. The measurement technique also helps to avoid operator variations in the measurements. Also increasing the accuracy is the fact that contact with the cornea is not needed, eliminating variations due to compression on the cornea. Since optical biometry measures to the center of the macula, it gives the refractive axial length versus the anatomic axial length achieved with ultrasound biometry.
Haag Streit - LENSTAR® allows measurements of not only axial length and keratometry, but it provides the white–to-white, pachymetry, lens thickness, anterior chamber depth, pupillometry, eccentricity of the visual axis, and retinal thickness. The LENSTAR® also defines anterior chamber depth more accurately as the distance from the posterior surface of the cornea to the anterior surface of the lens, rather than the anterior surface of the cornea to the anterior surface of the lens like many others do. The LENSTAR® takes keratometric readings at 1.65mm and 2.3mm, combining them via an iteration process for improved consistency.
All of the standard IOL prediction formulas (Holladay I, SRK-T, Haigis and Hoffer Q) are built into the software – with potential for future formulas to be added. Since the LENSTAR® measures more parameters of the eye than the traditional IOL formulas use, the system is ready to incorporate future generations of IOL formulas as they are developed. As a recent addition, the Olsen formula can now be used for calculations. Constants for use with the Olsen formula are available from data acquired by Dr. Olsen. Furthermore, constants for the toric IOL are available from IOL manufacturers. Download the LENSTAR® User Manual.
Carl Zeiss Meditec - Zeiss IOLMaster® The IOLMaster® was the first optical biometry model on the market since 1999. Since then, many advances have been made in this technology, although the IOL Master still provides accurate measurements, but uses slit imagery for some while others have progressed to optical biometry. Improvements have been made on this unit since its first development. For instance, Zeiss improved the ability to cut down on background noise when measuring through dense cataracts. The IOLMaster® has a very fast computer for the quick and reproducible acquisition of keratometry information. According to Carl Zeiss, the IOLMaster® is consistently accurate to within 0.02 mm (vs. 0.10mm to 0.12mm with A-scans). Download the IOLMaster® User Manual.