T Dada f Imaging Do's and Donts

7/28/2019 T Dada f Imaging Do's and Donts

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ONH and RNFL Imaging

Interpreting Results

Tanuj Dada

Additional Professor

Dr RP Centre for Ophthalmic Sciences

All India Institute of Medical Sciences

New Delhi


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Q.Why do we need Imaging ?


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WGA : New Glaucoma Definition

Progressive Structural

Optic Nerve Damage

is the NEW Gold Standard.


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Undetectable Disease May Progress

to Functional Impairment

VF=visual field.

Adapted from Weinreb et al.Am J Ophthalmol. 2004;138:458-467.

Normal

Acceleration of

apoptosis

Ganglion celldeath/axon loss

RNFL change(undetectable)

RNFL change(detectable)

SWAP VF changes

SAP VF change

VF change (moderate)

VF change (severe)

Blindness


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Does imaging add to clinical care ?

Nearly 50% of glaucoma patients did not have a disc drawing or

photograph taken at the time of initial examination

Fremont AM, Lee PP, Mangione CM, et al. Patterns of care for open-angle glaucoma in managed care. Arch

Ophthalmol. 2003;121:77783.

1. Baseline documentation of the disc changes

2. Evaluation of the disc size

3. Risk Assessment (OHTS CSLO study)

4. Early diagnosis

5. Documentation of progression

x Pallor, Hemorrhage


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WGA Recommendation

The World Glaucoma Association &

American Academy of Ophthalmology

recommend

Imaging as part of routine clinical care


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Q.

With so many high tech. machineswhy is there a problem in

diagnosing glaucoma withimaging ?


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Normal Biological Variability ?

Large variability in optic nerve head

0.7 1.5 million optic nerve axons

This huge Normal Variability

Limits ability to differentiate between

healthy eyes and glaucoma at one point in time


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Patient A presents with 1 million nerve fibers

Q1. Did he start of with 1 million (within normal range)

Q2. Did he start of with 1.4 million (within normal range)

Early Diagnosis : A myth

People in the statistically normal rangemayundergo optic disc and RNFL changes over

time and yet still remain within the normal

range on the basis of any single exam alone.


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Normative Databases are indicators and not

specific enough for definitive diagnosis

Glaucoma Diagnosis

We need to document progressivestructural loss over time

The patient is his own best normal and to

diagnose glaucoma you need to monitor

change over time


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Q.Test Re-Test Variability


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VariabilityScan done on 4rth march 2006 2.51 pm Scan done on 4rthmarch 2006 3.00 pm


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Triple Scan GDx Version 6.0


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Image Quality: Standard

Deviation< 10 m Excellent10 - 20 m Very Good

20 - 30 m Good30 - 40 m Acceptable

40 - 50 m Try to improve

> 50 m Poor quality

documentation

only


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Image Quality Standard

DeviationHigh quality images with low Standard

Deviations (7-30 m) allow us to detect

small changes.Lower quality images i.e. higher Standard

Deviations (30-50+ m) mean there is more

noise and thus changes need to be much

bigger before we can detect them.


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Image Quality

We want to compare similiar quality images to

be more assured that change is real and not

due to fluctuations in image quality

SD 10 SD 11 SD 12 SD 9 SD 10


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Image Quality

We want to compare similiar quality images to

be more assured that change is real and notdue to fluctuations in image quality


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Review Image Quality

Standard Deviations should ideally be

within 5m of each other

Exclude outliers from the Progression Series


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Astigmatism

Astigmatism introduces an optical rotation into theimage, affecting image quality.

This rotation must be corrected for using astigmatic

corrective lenses if the cylinder is more than 1D


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Q.Impact of signal strength ?


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Impact of Signal Strength on RNFL

Differences in signal strength were associated withdifferences in average RNFL thickness

Even under optimal testing conditions, scan quality can

adversely effect the ability to detect change over time

Therefore, caution is warranted when detectingglaucomatous progression using scan series

of different quality

Signal strength of > 7 is mandatory

Vizzeri G, Bowd C, Medeiros FA, Weinreb RN, Zangwill LM.

Am J Ophthalmol. 2009 Aug;148(2):249-255


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Signal Strength

Factors influencing

Lenticular opacification

Posterior capsule opacification

Ocular surface disease dry eye


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62 F CORTICAL

CATARACT OD

SIGNAL STRENGTH

6/10


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patient underwent

cataract surgery

OCT 4 weeks later

Post operative SD-OCT

SIGNAL

STRENGTH 8/10


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GDxVCC parameters pre and post

cataract surgery(Dada T et al. Indian J Ophthalmol. 2010 Sep-Oct;58(5):389-94 )

RNFL Parameters Pre operative Post operative P value

TSNIT average 49.2 14.1 56.5 7.6 0.001

Superior average 51.6 12.2 59.8 7.3 0.004

Inferior average 50.2 13.7 61.5 10.3 0.001

NFI 41.3 15.3 21.6 11.8 0.001


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BEFORE

Phaco IOL

AFTER

Phaco IOL


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Q.

How to increase the

signal strength ?


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Increasing Signal StrengthEnsure the Ocular Lens is Clean

Adjust Focus

Optimize PolarizationInstruct the patient not to blink during optimization

Ensure the scan is not too low horizontally

Stable Tear film ask patient to blink before scan is acquired

In case of media opacity , move the pupil alignment off-center by

clicking in a different spot on the pupil in the iris viewer or

adjusting the chinrest position.


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Q.Effect of Disc Size?


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False Positive HRT

Large Disc CD Ratio = 0.85: 1


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Disc Size : MRA, GPS

Jindal S, Dada T et al .Indian J Ophthalmol. 2010 Nov-Dec;58(6):487-92.Comparison of the diagnostic ability of Moorfield's regression analysis

and glaucoma probability score using Heidelberg retinal tomograph III in

eyes with primary open angle glaucoma (n =50)

The sensitivity increased with increasing disc sizefor both MRA and GPS and vice versa

There was a poor agreement between the overall

MRA and GPS classifications.


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Q.Effect of centration ?


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Before you

comment on

Progression

Check

Centration


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Q.Effect of IOP?


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IOP lowering can impact ONH

Check IOP from exam to exam

Changes of 2 or 3 mm Hg not significant

Changes of 10 mm Hg could be significant


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Q.Glaucoma with ARMD ?


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Scanning Laser Polarimetry (780 nm)

with variable corneal compensation

Is based on the principle that polarized light ischanged as it passes through the Retinal Nerve

Fiber Layer

Variable Corneal Compensation eliminates

the effect of Corneal Polarization

GDx VCC


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GDx VCC

Macular scan is performed

Henle fibers = uniform

birefringence

Abnormal Birefringence pattern

of Henle s Layer yields corneal

birefringence

Corneal birefringence is then

eliminated to give actual

RNFL thickness measurement

Macular birefringence

note bow tie pattern

without compensation


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Parameter Protocol I (a) Protocol II (b)p value

a vs. bProtocol I (c) Protocol II (d)

Normal Abnormal Macula

TSNIT Average 51.9 4.7 52.8 5.1 0.02 78.6 33.3 53.9 8.4

Superior Average 63.1 7.1 66.1 6.9 0.003 82.7 32.1 62.0 12.1

Inferior Average 58.8 7.5 59.9 6.7 0.2 77.7 31.9 59.9 10.7

NFI 22.7 9.2 19.3 8.6 0.01 14.2 14.1 25.8 16.9

Dada T , Dave V ARVO 2010


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Standard

Scan

Protocol

Irregular

Scan

Protocol


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Q.Effect of Peripapillary Atrophy?


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False Negative

Supra - Normal

Peripapillary

Atrophy

Problems with

GDxVCC


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J Glaucoma (2009)

3 scan diameter scans

2.4 - 3.2 mm

3.2 - 4.0 mm

4.0 - 4.8 mm


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Q.

Correlate fundus examination

with imaging and perimetry ?


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Correlation of structure & function


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Does an Abnormal Scan

indicates Glaucoma ?


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44 yr male open angle, CCT 530, IOP 20-22 mmHg


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A Word of Caution !

Imaging

Does not replace your clinical examination

Provides additional clinical information which is

useful in the diagnosis and management ofyour patients


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Take Home Message

Imaging is critical in diagnosis and

management of glaucoma

Expert operator and expert interpreter

Use your own eyes and brain in

conjunction with machinery

Check image quality at each visit and correlate

structural changes with functional deficits

Thank You


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Thank You


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Q.How to identify Progression ?

How to Diagnose :


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How to Diagnose :

Glaucoma progression

Exam 1 : RNFL thickness = 100 microns

December 2010


July 2011

Logical Conclusion = 3 microns loss of RNFL thickness

Patient has progressed : Initiate or escalate treatment


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Glaucoma progression

Must know test re-test variability




Truth : Normal Test Re-Test Variability is 6 microns

so you cannot take 3 micron loss as progression


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Baseline Imaging Exam

Must do test re-test variability to

establish range of variability

If change during follow up is more than

test re-test variability -

Only then can you call it a progression

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T Dada f Imaging Do's and Donts