Three-dimensional Neuroretinal Rim Thickness and Visual Fields in Glaucoma: A Broken-stick Model

Area of Science:

• Ophthalmology
• Medical Imaging
• Glaucoma Research

Background:

• Open-angle glaucoma (OAG) is a leading cause of irreversible blindness.
• Early detection of visual field (VF) damage is crucial for timely intervention in OAG.
• Neuroretinal rim tissue thickness, measurable by optical coherence tomography (OCT), is a key indicator of optic nerve health.

Purpose of the Study:

• To identify the specific threshold of neuroretinal rim tissue thickness below which visual field defects become detectable in open-angle glaucoma patients.
• To establish the relationship between structural measurements (MDB thickness, RNFL thickness) and functional deficits (VF damage).

Main Methods:

• Retrospective cross-sectional study involving 57 healthy and 100 OAG patients.
• Utilized spectral-domain OCT for retinal nerve fiber layer (RNFL) and optic nerve volumetric scans.
• Calculated minimum distance band (MDB) neuroretinal rim thickness using custom algorithms and performed broken-stick regression to determine tipping points.

Main Results:

• Visual field damage became detectable when global MDB thickness fell below 31% of normal.
• Specific thresholds for superior and inferior MDB thickness were identified as 36.8% and 43.6%, respectively.
• The structure-function relationship showed significantly steeper slopes below these thresholds, indicating accelerated VF loss.

Conclusions:

• Neuroretinal rim tissue thickness, specifically MDB thickness measured by OCT, is a reliable predictor of early visual field damage in open-angle glaucoma.
• A threshold of approximately one-third of normal MDB thickness signifies the onset of detectable VF defects.
• Findings support the use of OCT-derived MDB thickness for monitoring glaucoma progression and assessing functional loss.