Bruch's membrane opening-minimum rim width and visual field loss in glaucoma: a broken stick analysis

Area of Science:

• Ophthalmology
• Neuroscience

Background:

• Glaucoma is a progressive optic neuropathy characterized by visual field (VF) loss.
• The Bruch's membrane opening-minimum rim width (BMO-MRW) is a key anatomical parameter in glaucoma diagnosis and progression.
• Identifying the threshold of BMO-MRW loss that precedes detectable VF damage is crucial for early intervention.

Purpose of the Study:

• To determine the specific tipping point of Bruch's membrane opening-minimum rim width (BMO-MRW) loss at which visual field (VF) damage becomes statistically detectable.
• To investigate the relationship between BMO-MRW reduction and VF defects in glaucoma patients.

Main Methods:

• Spectral-domain optical coherence tomography (SD-OCT) was used to measure BMO-MRW in 85 normal subjects and 83 glaucoma patients.
• Visual field examinations were performed, and deviation values were mapped to corresponding sectors.
• A "broken-stick" statistical model analyzed the relationship between BMO-MRW measurements and VF loss to identify a tipping point.

Main Results:

• A global BMO-MRW loss of 25.9% from normative values was required for detectable VF loss.
• Sectorally, inferotemporal BMO-MRW thinning of 33.1% and superotemporal thinning of 8.9% were necessary for VF loss detection.
• VF loss was significantly related to BMO-MRW loss below the tipping point, but unrelated beyond it (P≤0.002).

Conclusions:

• Substantial BMO-MRW loss is a prerequisite for detectable visual field damage in open-angle glaucoma using standard achromatic perimetry.
• This indicates a critical structural threshold that must be breached before functional deficits become apparent.