Monday, 26 February 2018

Near infrared optical coherence tomography

I recently had a bit of a false alarm, or a false positive in data terms, with my eyes. A routine eye test threw up a structural condition that could result in glaucoma and so I was sent off to visit a specialist eye clinic. As I said, the problem wasn't actually there, but in the course of the test I came across a use of near-infrared light that was new to me: OCT or Optical Coherence Tomography.

The test experience was somewhat like that slit-scan sequence from the movie 2001, with me seeing moving rectangles and triangles expanding and contracting in my field of view. The result was a cross-sectional view of my retinas looking something like this:

This is an OCT scan of the cross-section of a retina at 800nm with an axial resolution of 3µm. Near infrared will easily penetrate a few millimetres into human tissue and by using a pulsed laser and a lot of computing an image of this type (described as being like 'visual ultrasound') can be built up. If you want to see the techicalities (and some maths) then check out the Wikipedia entry. The particular equipment used for my test was by a company named Optovue.

[Image is copyright: GNU-FDL, origin medOCT-group, Dept of Med. Physics, Med. Univ. Vienna, Austria, 2004 via Wikipedia]

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