Difference between a constant in optical and immersion
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Answer:
Immersion Vector-A/B-scan Biometry
A-scan biometry by immersion has better reproducibility, which leads to an overall increase in accuracy. The immersion technique can be performed rapidly and with greater confidence than the applanation method. Making the change from the applanation to immersion is well worth the small learning curve.
However, all forms of ultrasound based biometry have two basic limitations. First, they use a rather large 10-MHz sound wave to measure a relatively small distance. Second, the area around the center of the macula is not flat, but thinnest at the fovea, with thicker shoulders. In order to overcome these two accuracy barriers, axial length must be measured by partial coherence interferometry using the Carl Zeiss Meditec IOLMaster.
By the applanation biometry method, an ultrasound probe is placed directly on the cornea, which slightly indents the surface. More desirable, by the immersion technique the ultrasound probe does not come into direct contact with the cornea, but instead uses a coupling fluid between it and the probe, preventing compression.
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