Purpose To evaluate the effect of signal strength (SS) on optical coherence tomography (OCT) parameters, and devise an algorithm to adjust the effect, when acceptable SS cannot be obtained.
Methods 5085 individuals (9582 eyes), aged ≥40 years from the Singapore Epidemiology of Eye Diseases population-based study were included. Everyone underwent a standardised ocular examination and imaging with Cirrus HD-OCT. Effect of SS was evaluated using multiple structural breaks linear mixed-effect models. Expected change for increment in SS between 4 and 10 for individual parameter was calculated. Subsequently we devised and evaluated an algorithm to adjust OCT parameters to higher SS.
Results Average retinal nerve fibre layer (RNFL) thickness showed shift of 4.11 µm from SS of 5 to 6. Above 6, it increased by 1.72 and 3.35 µm to 7 and 8; and by 1.09 µm (per unit increase) above 8 SS. Average ganglion cell-inner plexiform layer (GCIPL) thickness shifted 5.15 µm from SS of 5 to 6. Above 6, increased by 0.94 µm from 7 to 8; and by 0.16 µm (per unit increase) above 8 SS. When compared with reference in an independent test set, the algorithm produced less systemic bias. Algorithm-adjusted average RNFL was 0.549 µm thinner than the reference, while the unadjusted one was 2.841 µm thinner (p<0.001). Algorithm-adjusted and unadjusted average GCIPL was 1.102 µm and 2.228 µm thinner (p<0.001).
Conclusions OCT parameters can be adjusted for poor SS using an algorithm. This can potentially assist in diagnosis and monitoring of glaucoma when scans with acceptable SS cannot be acquired from patients in clinics.
- optic nerve
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ST and MY are joint first authors.
Contributors ST, MY, C-YC, CC, PYB, TA and TYW conceived and designed the study. ST, MY, YCT and C-YC analysed and interpreted the data. ST, MY, YCT, SM, Z-DS and XLF wrote the manuscript. All authors reviewed and approved the final version of the manuscript.
Funding This study was supported by the National Medical Research Council, Singapore (grant nos: NMRC/CIRG/1417/2015, NMRC/CIRG/1488/2018; and NMRC/OFLCG/004a/2018).
Competing interests None declared.
Patient consent for publication Not required.
Provenance and peer review Not commissioned; externally peer reviewed.
Data availability statement All data relevant to the study are included in the manuscript or uploaded as supplementary material. However, additional data can be made available on reasonable request to the corresponding author. The algorithm mentioned in the manuscript is available at https://seri-seed.shinyapps.io/Cirrus-OCT-SS-Adjustment.
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