2 OPTICAL COHERENCE TOMOGRAPHY IN GLAUCOMA OCT3WelcomeClinical Aspects OfOPTICAL COHERENCE TOMOGRAPHY IN GLAUCOMAPresented byAkram Rismanchyin MDIsfahan University2008Anatomy 101 for Regional Managers
3 Glaucoma is an optic neuropathy characterized by a Typical parrem of visual field loss and optic nerve damage due to retinal gan'glion cell death caused by a number of differentdisorders that affect the eye: Most of these disorders are associated with elevated intraocular pressure (lOP), which is the most important risk factOr for glaucomatOus damage.
4 Although clinical examination of the optic nerve head has beenn considered to be the most sensitive test for detecting glaucomatOus damage, evidence suggests that examination of the retinal nerve fiber layer (RNFL)may provide important diagnostic information
5 Standard clinical techniques for assessing glaucOluatous changes, such as optic nerve head and NFL examination or visual fteld testingt lack sensitivity and reproducibility.
6 Visual evaluation of the optic nerve head by direct examination or by stereoscopic fundus photography is subjective, and the variability among experienced observers is often great
7 Visual field testing depends on patient cooperation and may also be influenced by non-glaucomatous vision Loss.Additionally) significant retiliainerve fiber layer loss mey precede both the development of visual field defects and identifiable cupping
9 Optical coherence tomography (OCT; Zeiss-Humphrey) Introduced in 1991Provides high-resolution cross-sectional imaging of the retina and the NFL.Is analogous to ultrasound B-scan imaging.A short coherence length diode source (850 nm).
11 Resolution Conventional ultrasound: 150 mic UBM 20 mic (penetration depth of4 mm)CTS and MRI several hundred micOCT I, II : micOCT III : 8-10 micUltra- High resolution OCT : 2-3 mic
12 ResolutionCorrelation between OCT and histopathologic examination revealed agreement for RNFL thicknesses within10 μmOCT may underestimate histological NFL thickness by an average of 37%(Jones et al, 2001)
13 The operation of OCT is based on the principle of low coherence interferometry
14 Light is directed onto a partially reflecting mirror and is split into reference and measurement beams.
15 The measurement beam is reflected from the eye with minutely different time delays depending on its internal microstructure..
16 When the two light beams coincide, they produce a phenomenon known as interference, which is measured by a photodetector.
20 OCT3 ImagesIn previous OCT images, we were able to see four layers of the retina. Now we are seeing 7, or sometimes 8.
21 We Now Believe That the Best Way to View OCT3 Images is in the B & W Mode. It Appears to Give More Details.OCT3 Images
22 Types of measurment in Glaucoma NFL thickness in the peripapillary regioncircular (3.4mm) linear tomogramOptic nerve head profileMacular volume (has a reverse correlation with glaucoma damage)
23 Other Clinical applications Corneal thickness (Hoerauf et al. 2000)Anterior chamber depth (Hoerauf et al. 2000) for the diagnosis of angle closure glaucoma.Iris thickness and profile (Hoerauf et al. 2000), potentially useful for plateau iris, pigment dispersion and angle closure glaucoma.
30 Scan ImageThe image with the lowest signal strength or with a data message will be shown to facilitate operator review.
31 Signal Strength Numbers range from 0 (weak) to 10 (strong). images with a signal strength below 5 should not be used.
32 Sector Averages Quadrant Averages Comparison to normative data in each sector is indicated with stoplight color scheme.Values are displayednumerically.Quadrant AveragesComparison to normative data in each quadrant isindicated with stoplight color scheme.Values are displayednumerically.
33 OCT3 Analysis ProgramThe NEW OCT3 Analysis program is a software addition, providing normative data and statistical analysis for both retina and glaucoma applications. Data was collected on over 1200 eyes, at four centers in the US. The protocol of this study enabled Zeiss Humphrey Systems to establish an age-related normative database for Macular thickness and Retinal Nerve Fiber Layer thickness.
34 The mean RNFL thickness alone has a sensitivity of 84% and a specificity of 98% if its value is abnormal at the 5% level.If 1 clock-hours or 1 quadrants are abnormal at the 5% level, the sensitivity for glaucoma is 89% and the specificity is 92% to 95%, respectively
35 OD/OS GraphTSNIT line graph displays RNFL thickness in both eyes.Asymmetry may be indicative of glaucomatous loss.
36 LegendNormative data is displayed in stoplight color code, described in detail on insideback cover.
37 Best parameters for Sratus OCT >or=1 quadrants abnormal p<5%>or=1 clock hours abnormal at p<5%
38 OCT RNFL Thickness Analysis – OU Overlay OD in BlueOS in Green“Normal” eyes =Similar shapeAbnormal eyes =Dissimilar shapeLoss of RNFL in OS Superior “Hump” May be an Indication of Pathology
39 For each eye, values are compared to normative data and displayed in Tabular DataFor each eye, values are comparedto normative data and displayed instoplight color code, described in detailon inside back cover.
40 OCT Differentiates glaucomatous from non-glaucomatous eyes Normal NFL thickness (with 3.4mm circular) (133+/- 17) Inferior(130+/- 18) Superior(80+/- 18) Nasal (75+/- 17) Temporal(105 +/- 11) meanBut the normal and abnormal ranges overlap
41 In new versions of OCT it is evaluated about symmetry of NFL (nerve fiber layer symmetry test) Superior and inferior half divided to 3 to 5 segment and thickness of NFL compare with each other in each segment
42 ABILITY TO DETECT CHANGE Change analysis software has recently been introducedHowever, statistical units of change probability are not providedIt is difficult to differentiate true physiologic change from test-retest variability.
43 RNFL Thickness Serial Analysis Comparative analysis of RNFL thickness over time. Can be applied to up to 4 OD and/or 4 OS scan groups
44 Optic Nerve Head Analysis Objectively finds Margin of Disk using signal from end of Retina Pigment EpitheliumNot accurate on:- Peripapilary Atrophy- Staphyloma
45 Optic Nerve Head Analysis Radial line scans through optic disc provide crosssectional information on cupping and neuroretinal rim areaDisc margins are objectively identified using signal from end of RPEKey parameters include cup-to-disc ratio and horizontal integrated rim volume
46 Optic Nerve Head Analysis Objectively finds Cup and calculates volumes and areas of the ONHUser can modify placement of diskDoes not require reference plane as with other technologies
69 OCT Advantages Noninvasive Non-contact High resolution High sensitivityNot affected by axial length and refractionNot affected by moderate nuclear sclerotic cataracts.
70 ADVANTAGES Objective, quantitative, reproducible In contrast with other imaging techniques, direct measurements of the RNFLAn anterior segment compensator is unnecessary and structural information is independent of a reference plane.
71 DISADVANTAGES High cost Posterior subcapsular and cortical cataracts impairs performanceCurrently change analysis software lacks statistical units of change probability, making it difficult to differentiate biological change from measurement variability.
72 Imaging versus examination The quantitative methods HRT, SLP, and OCT were no better than qualitative assessment of ONH by experienced observers at distinguishing normal eyes from those with early to moderate glaucoma.
73 In SummaryIt is not recommended that clinical decisions be based on the results of any single imaging test, as with visual field testing.Clinical correlation is essential and management must be tailored to each individual patient.