The colour on an OCT deviation map is not a measurement of the patient's optic nerve. It is a comparison against a normative database, and those databases are built predominantly from eyes of average axial length. An eye that is markedly long or markedly short is being compared with eyes it does not resemble.
So before acting on a red sector, look at the axial length and the refraction, and ask whether the pattern makes anatomical sense. Then look at the raw B-scan, not just the map. Segmentation errors, tilted discs, peripapillary atrophy and vitreous opacity all produce colour, and all are visible on the underlying scan if you open it.
The practical rule is that structure must agree with something else before it changes management — the disc appearance, the visual field, or a second scan over time. A single abnormal deviation map in a long eye is a reason to look harder, not a reason to start treatment.
- Read the axial length and refraction before interpreting any deviation map
- Open the B-scan and check segmentation before believing a colour-coded sector
- Look for tilted disc and peripapillary atrophy, which generate colour in normal eyes
- Require agreement between structure and disc appearance or field before changing management
- In a long eye, treat an isolated abnormal map as a prompt to repeat and correlate, not to treat
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