Retinal nerve fiber layer reflectometry must consider directional reflectance.

Area of Science:

• Ophthalmology
• Biomedical Optics
• Glaucoma Research

Background:

• Retinal nerve fiber layer (RNFL) thickness is a common glaucoma metric.
• RNFL reflectance offers more sensitive glaucoma detection.
• Directional reflectance of RNFL is a significant source of measurement variability.

Purpose of the Study:

• To quantitatively compare RNFL directional reflectance using an angular spread function (ASF).
• To analyze how scattering angle, wavelength, distance from optic nerve head (ONH), and bundle thickness (T) affect ASF parameters (amplitude A, width W).

Main Methods:

• Characterized ASF by amplitude (A) and width (W).
• Expressed internal reflectance as A/T.
• Measured reflectance at varying scattering angles, wavelengths, and distances from the ONH for different bundle thicknesses.

Main Results:

• RNFL amplitude (A) varied significantly with scattering angle and wavelength.
• Internal reflectance (A/T) differed between bundles but was constant along individual bundles.
• ASF width (W) increased near the ONH and at longer wavelengths, independent of scattering angle or T.
• A 4.3° change in incident angle altered reflected intensity by a factor of 2.7.

Conclusions:

• RNFL internal structure varies between bundles but not with distance from the ONH.
• Accounting for directional reflectance is crucial for improving accuracy and reproducibility in RNFL reflectance measurements.
• Directional reflectance analysis enhances glaucoma detection sensitivity over RNFL thickness alone.