Retinal Nerve Fibre Layer Thickness Increases with Decreasing Spectralis OCT Signal Strength in Normal Eyes.

Area of Science:

• Ophthalmology
• Medical Imaging
• Retinal Imaging

Background:

• Optical coherence tomography (OCT) is crucial for measuring retinal nerve fibre layer (RNFL) thickness.
• Previous studies using Cirrus and Stratus OCT suggested signal strength affects RNFL measurements.
• Understanding factors influencing RNFL measurements is vital for accurate diagnosis and monitoring of eye conditions.

Purpose of the Study:

• To investigate the impact of signal strength on mean RNFL thickness measurements.
• To determine the relationship between signal strength (Q value) and RNFL thickness using Spectralis OCT.
• To compare findings with previous observations from other OCT devices.

Main Methods:

• Thirty healthy subjects underwent imaging with Spectralis OCT.
• Variable Bangerter foils were used to systematically reduce signal strength (Q value).
• Statistical analysis was performed to assess the correlation between Q value and RNFL thickness.

Main Results:

• A statistically significant linear relationship was observed between Q value and RNFL thickness (R = 0.8643, p < 0.01).
• A decrease in Q value (signal strength) correlated with an increase in mean RNFL thickness (1 unit Q decrease = 0.181 µm RNFL increase).
• Contrary to prior studies, RNFL thickness did not decrease with decreasing signal strength in Spectralis OCT.

Conclusions:

• Spectralis OCT demonstrates a unique behavior where RNFL thickness increases as signal strength decreases.
• This finding contrasts with previous reports from Cirrus and Stratus OCT devices.
• Clinicians should be aware of this inverse relationship when interpreting Spectralis OCT RNFL measurements.