FLOOR EFFECT ON OCT

 

In advanced glaucoma, OCT of the optic nerve head (ONH)/retinal nerve fiber layer (RNFL) can give rise to various errors and may not be an ideal investigation for such patients.

As glaucoma advances, RNFL measurement continues to decrease, but it doesn’t go to zero. This is known as the “floor effect.”

The “floor effect” is defined as the point at which no further structural damage can be measured.

This happens because the architectural support made up of Müller cells, astroglia, microglia, and blood vessels doesn’t degenerate completely with retinal ganglion cell axons.

This floor effect, possibly due to the presence of residual tissue (e.g., glial cells, blood vessels) or failure of tissue segmentation algorithms (i.e., an artefactual floor), is thought to be a serious problem for monitoring structural changes in eyes with advanced glaucoma.

Even though the patient with advanced disease may be progressing, it is often challenging to detect any observable change with optical imaging. In these eyes, monitoring of disease must rely on standard automated perimetry (SAP) or other visual function tests. Although SAP is a standard clinical test, SAP measurements of visual sensitivity are notoriously variable, particularly as glaucoma severity increases.

This patient was observed to have 0.9 C:D R in both eyes on slit-lamp examination. However, the OCT shows 0.9 in the left eye only and 0.56 in the right eye. This is likely from the floor effect, as the scan is eccentric and not assessing the floor of the cup.

FURTHER INFO:

https://www.aao.org/eyenet/article/estimating-oct-structural-measurement-floors-to-de#:~:text=In%20retinal%20imaging%2C%20the%20%E2%80%9Cfloor,floor%20in%20patients%20with%20glaucoma.