Q 1 – What affects retinal nerve fiber layer thickness (RNFL) measured by OCT?
1 Retinal artery coming from the optic disc
2 Retinal veins coming from the optic disc
3 Both 1 and 2
Q 2 – Location of which vessel is a good predictor of the variation in the retinal nerve fiber layer (RNFL) thickness profile?
1 Major nasal blood vessels
2 Major temporal blood vessels
3 Major inferior blood vessels
4 Major superior blood vessels
Q 1 Answer: 3
Blood vessels must influence the RNFL thickness measured with OCT. Retinal arteries coming from,
and veins going to, the optic disc travel in the RNFL and contribute to its thickness. In fact, the presence of these blood vessels can be inferred from the shadows they cast in OCT images, which can be identified easily in normal retinal nerve fiber layer and also when there is significant retinal nerve fiber layer thinning when they become even more prominent and may be responsible for segmentation errors.
Q2 Answer: 2
The RNFL thickness profiles measured with OCT vary across individuals, even when refractive
error and scan quality are taken into consideration.
This variation in RNFL profiles is large relative to that found owing to measurement error, age, or the size of the optic disc.
The location of the major temporal blood vessels can
help us understand this variation. Largely the superotemporal vessels and the inferotemporal vessels indicate the area and course of the thickest part of the RNFL.
Hood DC, Fortune B, Arthur SN, Xing D, Salant JA, Ritch R, Liebmann JM. Blood vessel contributions to retinal nerve fiber layer thickness profiles measured with optical coherence tomography. J Glaucoma. 2008 Oct-Nov;17(7):519-28. doi: 10.1097/IJG.0b013e3181629a02. PMID: 18854727; PMCID: PMC2987575.