2 Clinical MismatchMismatch between clinically visible disc margin & SD-OCT-based disc marginSD-OCT BMOObvious mismatch between clinician´s opinion and the SD-OCT-based disc margin. Where is the clinician looking for? Brightness changes (reflectivity), scleral ring (pale band), bending vessels, symmetry considerations.How does the SD-OCT define the disc margin? Are there anatomical landmarks the instrument is using as referring points? > Bruch´s Membrane Opening (BMO)Clinically Visible Optic Disc MarginImage Courtesy Dr. Balwantray C. Chauhan, Halifax, Canada and Dr. Claude F. Burgoyne, Portland, USA.
3 Variable Rim Tissue Internally oblique Non-oblique Externally oblique Image Courtesy Dr. B.C. Chauhan, Halifax, Canada.Clinical disc marginBMOReis et al. Ophthalmology 119: ,2012.
4 Clinical Disc Margin Conclusion The clinical optic disc margin is hard to identifyIn practice the clinician is looking at 3 different tissues when defining the disc marginBMO (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 rimEach individual ONH can have regions of internally and / or externally oblique border tissuesClinician sees BMO (1), some aspect of border tissue of Elschnig (2) or indetermined structures of border tissue or Elschnig(3).Most predominant structure recognized as DM is some aspect of border tissue.BMO mostly invisible for clinician and by photography. Only SD-OCT able to detect deeper, relevant anatomical landmarks. Current disc margin delineation often inconsistent, inter-individually not always reproducible.
5 Overestimation of Rim Tissue ConsequencesInconsistent 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.DMBMOImage Courtesy Dr. B.C. Chauhan, Halifax, Canada.An overestimation of rim tissue means the patient appears to be healthier than he/she actually is. The image to the right shows a significant mismatch of the clinical DM and the SD-OCT based DM. Clinical DM underestimates the remaining rim; whereas SD-OCT based disc margin is far outside.
6 Invisible BMOBruch's Membrane Opening is a consistent landmark, but it is usually clinically and photographically invisible.BMOONLY SD-OCT makes the BMO visible.No more vague interpretations of disc marginoperator-independentreproducibleImage Courtesy Dr. B.C. Chauhan, Halifax, Canada.
7 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.Reis et al. Invest Ophthalmology Vis Sci. 53: , 2012.BMO-MRW
8 Correct Rim Measurement Reis et al. Invest Ophthalmology Vis Sci. 53: , 2012.BMO-MRWNeuroretinal rim measurement from BMO to nearest point on internal limiting membrane (ILM)Shortest distance measurementQuantification of perpendicular cross section of nerve fibers exiting the eyeTaking into account their varying trajectory at all 48 points of measurementBasic InformationCross Section of RNF
9 Current RealityCurrent sectorial analysis is made with fixed horizontal and vertical axes on the image.AIF Horizontal (N/T) AxisAIF Vertical (S/I) AxisAcquired Image Frame (AIF)
10 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
11 Anatomically Normalized Eyes Anatomically consistent landmark in all human eyesBMO is a true anatomic boundary of the RGC axonsBMOcentroid is the center of BMOFovea is the anatomic center of the retinaRGC axons organized relative to the FoBMO axisGeometric perspectives:The justification of choosing FoBMO axis is based on the anatomy.Both fovea and BMO centroid are anatomically consistent landmarks in human eyes.D. Hood and colleagues: retinal ganglion cell axons organized in a way along the FoBMO axisFigure 15.Changes in the RNFL bundle projections with different locations of the optic disc. (A) A digitally red-filtered fundus photo with tracings of 3 RNFL bundles in red. (B) Tracings as in panel A for 11 eyes. The green square with the red dot is the center of the optic disc. The open green square is the location on the disc associated with the RNFL originating at the 3 o'clock position on the red circles around the fovea. (C) Tracings from panel B after scaling and rotating to align the centers of the optic discs.From: D. Hood et al., Glaucomatous Damage in the Macula, Prog Retin Eye Res 2013; 1-21.
12 Anatomic Positioning System - APS BMOFoveaFoBMO - Axis
13 Anatomic Positioning System - APS Locates points in the eye using two fixed, structural landmarkscenter of the fovea andcenter of the Bruch’s Membrane Opening (BMO)Automatic detection of landmarks during initial APS scanAutomatic alignment of scans relative to patient’s individual Fovea to - Bruch’s Membrane Opening (FoBMO) center axisConsistent, accurate placement of subsequent scans and sectors for data analysisAutomatic adjustment for head tilt during acquisitionKey Feature !!!
14 Anatomic Positioning System - APS Without SPECTRALIS APSSame eye scanned on separate visits (no APS or AutoRescan)Head tilt causes significant variability of classification results
15 Anatomic Positioning System - APS With SPECTRALIS APSConsistent positioning for each individual’s anatomyTwo 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
16 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 AnalysisEasy correlation between analysis methodsUnique to SPECTRALIS !!!
17 Anatomic Positioning System - APS AdvantagesAutomaticIndividual / CustomizedConsistentReliableNo other OCT offers this functionality !!!
18 SPECTRALIS Glaucoma Module Premium Edition Rim analysis: IR image + SD-OCT B-scanClassification into WNL, Borderline and ONLBMO Rim Analysis
19 SPECTRALIS Glaucoma Module Premium Edition Garway-Heath Sectors40°110°90°Same eye – different sector distributionCurrent SectorsReferences:Garway-Heath DF et al. Mapping the Visual Field to the Optic Disc in Normal Tension Glaucoma Eyes. Ophthalmology 2000; 107: 1809–1815.AdvantagesSector orientation aligned with nerve fiber bundle trajectoryBetter structure-function correlation
20 SPECTRALIS Glaucoma Module Premium Edition New DisplayDifferent eyes – different displaysActual thickness(Percentile)Current ClassificationPercentile:Percentage of normal eyes have a rim this thin or thinnerActual thickness(Mean thickness value)Remember HRT !!!
21 SPECTRALIS Glaucoma Module Premium Edition Internally oblique atnasal sideExternally oblique attemp. sideBMO Overview gives information on the overall status of the ONH. Color of arrows (BMO-MRW) dependent on classification of corresponding sector.Corresponding fundus camera image can be loaded and displayed in center instead of IR image showing disc margin based on SD-OCT image.Within normal limitsBorderlineOutside normal limitsBMO Overview
22 SPECTRALIS Glaucoma Module Premium Edition „Beyond one´s own nose“Progression