Influence of coherence length, signal-to-noise ratio, log transform, and low-pass filtering on layer thickness assessment with OCT in the retina

Abstract

Optical coherence tomography (OCT) images of the retina are inevitably affected by the finite width of the coherence function and noise. To make low-reflective layers visible, the raw OCT signal is log transformed; to reduce the effect of noise the images can be low-pass filtered. We determined the effects of these operations on layer thickness assessment, as a function of signal-to-noise ratio (SNR), by performing measurements in a phantom eye and modeling. The log transform appeared to be the key factor in a SNR-dependent overestimation of peak widths and a less predictive bias in the widths of low-reflective layers.

Influence of optic disc-fovea distance on macular thickness measurements with OCT in healthy myopic eyes

“…Most of the subjects included in our study were young myopic subjects (Table 1 ). It has been reported that the image quality of OCT scans affects the observed retinal layer thicknesses 37 – 39 , and image quality decreases with an increase in myopia 40 . Consistent with Lee et al .…”

Testing a phantom eye under various signal-to-noise ratio conditions using eleven different OCT devices

“…Similarly, thickness measurements of low-reflective layers underestimate the real thickness. This over-and underestimation are less pronounced, and should theoretically disappear completely, if the analysis is based on linear-scale images [19]. The phantom layer addressed in the current study is neither a high-reflective nor a low-reflective layer, but is preceded by a layer with a lower reflectivity and followed by a layer with higher reflectivity [Figs.…”

“…Images may also be compressed to fit the commonly used 8-bit depth of monitors. In order to get unbiased thickness estimates, however, the untransformed, referred to as linear-scaled image in this article, data are needed [19].…”

Ultra-high resolution polarization-sensitive optical coherence tomography for imaging of the retinal nerve fiber layer

“…retina could be carefully be quantified, again of a large area around the optic nerve. Recent measurements on a retinal phantom however, have shown that these measurements may not be reliable [8][9][10] , as the thickness of the retinal nerve fiber layer cannot be determined reliably. Another issue is caused by glial content.…”