What an OCT scan is, and why we do it
Dr. Swati Goyal · 10 September 2024 · 4 min
OCT — optical coherence tomography — is an advanced test that tells us about the optic nerve and the retina. In everyday speech it is sometimes called a colour X-ray of the eye.
The retina is a structure of ten layers, and the naked eye cannot see that level of detail. That is why this test is advised — to catch disease before it announces itself.
What it shows
A colour fundus photograph is taken alongside, which helps in following the progression later. The OCT itself helps chiefly with two things — disorders of the retina, and the progression of glaucoma.
On the retina it shows whether fluid is collecting within the normal layers and contour; whether drusen or calcific or cholesterol deposits have formed; and if fluid has collected, how deep and how widespread it is.
Why it is repeated
Depending on how severe the condition is, the scan is repeated at six months or a year. Comparing the new scan against the old one tells us how well the treatment is working, and whether the disease is stable or progressing.
It is on all this that we decide how the treatment should go forward.