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SD-OCT BMO

Clinically Visible Optic Disc Margin

Image Courtesy Dr. Balwantray C. Chauhan, Halifax, Canada and Dr. Claude F. Burgoyne, Portland, USA.

Clinical Mismatch

Mismatch between clinically

visible disc margin &

SD-OCT-based disc margin

Variable Rim Tissue Internally oblique

Non-oblique

Reis et al. Ophthalmology 119:738-747,2012.

Externally oblique

Image Courtesy Dr. B.C. Chauhan, Halifax, Canada.

Clinical disc margin

BMO

Conclusion

The clinical optic disc margin is hard to identify In practice the clinician is looking at 3 different tissues when defining

the disc margin

BMO (1), RPE tips (endings; 2), some aspect of border tissue of Elschnig (3)

The clinical disc margin is inconsistent as an anatomical landmark

for the outer border of the rim

Each individual ONH can have regions of internally and / or externally

oblique border tissues

Clinical Disc Margin

Consequences

Inconsistent definition of the

disc margin can mean an

underestimation of rim tissue.

Using Bruch´s membrane opening (BMO)

as a stable landmark provides a more

accurate measurement of the ONH rim tissue.

DMBMO

Image Courtesy Dr. B.C. Chauhan, Halifax, Canada.

Overestimation of Rim Tissue

Invisible BMO

Bruch's Membrane Opening is a consistent landmark,

but it is usually clinically and photographically invisible.

Image Courtesy Dr. B.C. Chauhan, Halifax, Canada.

BMO

Even if BMO is used as a stable landmark by SD-OCT,

we still need to measure the neuroretinal rim in the correct

geometric orientation.

Geometric Orientation

Reis et al. Invest Ophthalmology Vis Sci. 53: 1852-1860, 2012.

BMO-MRW

Correct Rim Measurement

Bas

ic In

form

atio

n

Neuroretinal rim measurementfrom BMO to nearest point on internal limiting membrane (ILM)

Shortest distance measurement

Quantification of perpendicular cross section of nerve fibers exiting the eye

Taking into account their varyingtrajectory at all 48 points of measurement

Reis et al. Invest Ophthalmology Vis Sci. 53: 1852-1860, 2012.

BMO-MRW

Cross Section of RNF

Current Reality

Current sectorial analysis

is made with fixed horizontal

and vertical axes on the image.

AIF Vertical (S/I) Axis

Acquired Image Frame (AIF)

AIF Horizontal (N/T) Axis

Inter-individual variability in the axis connecting the

Fovea and Bruch’s Membrane Opening (BMO) center

Range of Variability of FoBMO Axes

+ 2° to

- 18° *<* Examples taken from the HDEng SPECTRALIS normative data collection

Anatomically consistent landmark in all human eyes

BMO is a true anatomic boundary of the RGC axons BMOcentroid is the center of BMO Fovea is the anatomic center of the retina RGC axons organized relative to the FoBMO axis

From: D. Hood et al., Glaucomatous Damage in the Macula, Prog Retin Eye Res 2013; 1-21.

Anatomically Normalized Eyes

Anatomic Positioning System - APS

Fovea

BMO

FoBMO - Axis

Anatomic Positioning System - APS Locates points in the eye using two fixed, structural landmarks

center of the fovea and center of the Bruch’s Membrane Opening (BMO)

Automatic detection of landmarks during initial APS scan

Automatic alignment of scans relative to patient’s individual Fovea to - Bruch’s Membrane Opening (FoBMO) center axis

Consistent, accurate placement of subsequent scans and sectors for data analysis

Automatic adjustment for head tilt during acquisition

Anatomic Positioning System - APS

Without SPECTRALIS APS

Same eye scanned

on separate visits

(no APS or AutoRescan)

Head tilt causes significant variability of classification results

Anatomic Positioning System - APS

With SPECTRALIS APS Consistent positioning for

each individual’s anatomy

Two eyes with different

anatomical positions of

fovea relative to the center

of the BMO (A and B)

Scan orientation automatically aligned along the individual’s FoBMO axis

Anatomic Positioning System - APS

Accurate geometric relations between nerve fiber defects can be established,

which are observed in ONH, RNFL and the Posterior Pole Asymmetry Analysis

Easy correlation between analysis methods

Anatomic Positioning System - APS

Advantages Automatic

Individual / Customized

Consistent

Reliable

BMO Rim Analysis

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Current Sectors Garway-Heath Sectors

40°

110°90°

40°40°

40°

Same eye – different sector distribution

References:Garway-Heath DF et al. Mapping the Visual Field to the Optic Disc in Normal Tension Glaucoma Eyes. Ophthalmology 2000; 107: 1809–1815.

Advantages

Sector orientation aligned

with nerve fiber bundle

trajectory

Better structure-function

correlation

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Current Classification

Percentile: Percentage of normal eyes

have a rim this thin or thinner

Actual thickness(Mean thickness value)

New Display

Different eyes – different displays

Actual thickness(Percentile)

Remember HRT !!!

BMO Overview

Within normal limits

Borderline

Outside normal limits

Internally oblique at nasal side

Externally oblique at temp. side

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Progression

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BMO-MRW OU Report

BMO Size: 1.85 mm2 BMO Size: 1.85 mm2

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BMO-MRW & RNFL Single Eye Report