Light versus sound

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As more practitioners obtain OCT devices, many will have access to anterior OCT measurement capability. As well as offering a view of the cornea in cross-section (along with the pre-tear film and contact lens if present) and views of the filtration angle, such measurements are also able to give pachymetry readings. In essence, instead of bouncing sound off reflecting layers perpendicular to the sound wave transmission and therefore calculating the thickness of any structure by analysis of the difference in time between receiving the echo from the front and the back surface, an OCT will measure the thickness by looking at the reflection of light from the two surfaces and calculating thickness in terms of the reflection delay from the more distant surface. I was interested to see if there was any significant difference between the two techniques.