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SPECTRALIS® Glaucoma Module
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Clinical Mismatch
Mismatch between clinically
visible disc margin &
SD-OCT-based disc margin
SD-OCT BMO
Clinically Visible
Optic Disc Margin
Image Courtesy Dr. Balwantray C. Chauhan, Halifax, Canada and
Dr. Claude F. Burgoyne, Portland, USA.
Variable Rim Tissue
 Internally oblique
 Externally oblique
 Non-oblique
BMO
Image Courtesy Dr. B.C. Chauhan, Halifax, Canada.
Reis et al. Ophthalmology 119:738-747,2012.
Clinical
disc margin
Clinical Disc Margin
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
Overestimation of Rim Tissue
Consequences
 Inconsistent definition of the
disc margin can mean an
underestimation of rim tissue.
 Using Bruch´s membrane opening (BMO)
DM
BMO
Image Courtesy Dr. B.C. Chauhan, Halifax, Canada.
as a stable landmark provides a more
accurate measurement of the ONH rim tissue.
Invisible BMO
 Bruch's Membrane Opening is a consistent landmark,
but it is usually clinically and photographically invisible.
BMO
Image Courtesy Dr. B.C. Chauhan, Halifax, Canada.
Geometric Orientation
 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.
BMO-MRW
Reis et al. Invest Ophthalmology Vis Sci. 53: 1852-1860, 2012.
Basic Information
Correct Rim Measurement
 Neuroretinal rim measurement
from BMO to nearest point on
internal limiting membrane (ILM)
BMO-MRW
 Shortest distance measurement
 Quantification of perpendicular
cross section of nerve fibers
exiting the eye
Reis et al. Invest Ophthalmology Vis Sci. 53: 1852-1860, 2012.
 Taking into account their varying
trajectory at all 48 points of
measurement
Cross Section of RNF
Current Reality
 Current sectorial analysis
is made with fixed horizontal
and vertical axes on the image.
AIF Horizontal (N/T) Axis
AIF Vertical (S/I) Axis
Acquired Image Frame (AIF)
Range of Variability of FoBMO Axes
 Inter-individual variability in the axis connecting the
Fovea and Bruch’s Membrane Opening (BMO) center
<
+ 2°
to
- 18°
*
* Examples taken from the HDEng
SPECTRALIS normative data collection
Anatomically Normalized Eyes
 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.
Anatomic Positioning System - APS
BMO
Fovea
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
 Consistent
 Individual / Customized
 Reliable
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BMO Rim Analysis
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Current Sectors
Garway-Heath Sectors
Advantages
90°
110°
 Sector orientation aligned
with nerve fiber bundle
trajectory
 Better structure-function
correlation
 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.
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Current Classification
New Display
Percentile:
 Percentage of normal eyes
have a rim this thin or thinner
Actual thickness
(Mean thickness value)
Actual thickness
(Percentile)
 Different eyes – different displays
 Remember HRT !!!
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Internally
oblique at
nasal side
Externally
oblique at
temp. side
Within normal limits
Borderline
Outside normal limits
BMO Overview
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Progression
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BMO Size: 1.85 mm2
BMO Size: 1.85 mm2
BMO-MRW OU Report
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BMO-MRW & RNFL Single Eye Report