Retinal nerve fibre layer thickness floor and corresponding functional loss in glaucoma

Area of Science:

• Ophthalmology
• Medical Imaging
• Glaucoma Research

Background:

• Glaucoma is a leading cause of irreversible blindness.
• Retinal nerve fibre layer (RNFL) thickness is a key indicator in glaucoma diagnosis and monitoring.
• Understanding the limits of RNFL measurement is crucial for accurate glaucoma assessment.

Purpose of the Study:

• To determine the minimum measurable retinal nerve fibre layer (RNFL) thickness in glaucoma patients.
• To correlate RNFL thickness floor with corresponding visual field (VF) sensitivity loss.
• To compare RNFL measurement floors between Spectralis and RTVue devices.

Main Methods:

• Review of visual field (VF), Spectralis RNFL, and RTVue RNFL data from glaucoma patients and healthy subjects.
• Application of two Bayesian change point models to estimate global and quadrant residual RNFL thicknesses.
• Correlation of estimated RNFL thicknesses with corresponding VF losses.

Main Results:

• RNFL thinning reached a measurement floor at different visual field loss levels for Spectralis and RTVue devices.
• Nasal and temporal RNFL quadrants consistently showed thinner residual layers compared to superior and inferior quadrants.
• No significant differences were found in post-change point residual RNFL thicknesses between the two models used.

Conclusions:

• The Spectralis device indicated a lower visual field loss threshold for RNFL thinning floor compared to RTVue.
• RNFL measurements below determined minimums provide limited clinical value.
• Findings highlight the importance of device-specific interpretation of RNFL thickness in glaucoma management.