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Optic Nerve Imaging. Management of Glaucoma

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(1)

Optic Nerve Imaging

in the Diagnosis and

in the Diagnosis and

Management of Glaucoma

Scott D. Smith, MD, MPH

Associate Professor of Clinical Ophthalmology Associate Professor of Clinical Ophthalmology

Director, Glaucoma Service Columbia University, New York, NY

Glaucoma Diagnosis

• Involves numerous

• Involves numerous diagnostic modalities

– IOP measurement – Optic disk examination – Visual field testing

• Inter-individual variability in optic disk makes early diagnosis difficult

(2)

Glaucoma Progression

• Detection of glaucoma progression has • Detection of glaucoma progression has

numerous obstacles

– Lack of standardized definition of progression

– Test-retest variability (visual fields)

– Subjective assessment of serial disk photos

Imaging and Glaucoma

• Technological advances in ophthalmic • Technological advances in ophthalmic

imaging offer potential improvement in identification of structural abnormalities caused by glaucoma

– Optic nerve head

(3)

Imaging and Glaucoma

• Multiple instruments each based on • Multiple instruments each based on

different imaging principles

– Confocal scanning laser ophthalmoscopy • Heidelberg Retinal Tomograph

– Scanning laser polarimetry • GDx

– Optical coherence tomography

Reproducibility

• To be useful any new imaging • To be useful, any new imaging

instrument must be reproducible

– Improved in some cases by averaging of multiple scans

E h h b h t h d

– Each has been shown to have good reproducibility

(4)

HRT

• Diode laser (670 nm)

– 15 x 15 degree scan (384 x 384 point grid) – Resolution: • 300 µm axial • 10 µm transverse • 3-D image of ONH – Series of 16 to 64 2-dimansional scans

HRT

• Operator defined • Operator defined optic disk margin

(5)

HRT

• Contour line defines • Contour line defines

the “reference plane”

HRT

• HRT measurements are strongly related • HRT measurements are strongly related

to the reference plane location

(6)

HRT III

• Improved software • Improved software

• Single image analysis does not depend upon user-identified optic disk margin • Improved progression analysis

(7)

HRT

• Indirect measure of RNFL thickness • Indirect measure of RNFL thickness

– Confounding by non-glaucomatous variation in optic nerve head anatomy – Poor performance in distinguishing

glaucoma from normal in population-based studies

studies

• Sensitivity 65% • Specificity 83%

(8)

GDx

• GDx measures thickness of retinal NFL • Scanning laser polarimetry

– Measures birefringence of RNFL – Birefringence

varies with RNFL thickness RNFL thickness

(9)

GDx

• Uses diode laser light source (780 nm) • Uses diode laser light source (780 nm) • 20 x 20 degree measurement area • Data displayed as 256 x 256 pixel grid

GDx

• Artifact in NFL thickness measurement • Artifact in NFL thickness measurement

introduced by birefringence of other ocular structures

– Cornea

• Older generation of instrument adjusted g j for expected corneal birefringence

(10)

GDx VCC

• Variable Corneal Compensation (VCC) • Variable Corneal Compensation (VCC)

– Allows measurement of individual corneal birefringence

– Compensates for individual differences – Improves reliability and detection of early

l

(11)
(12)

Optical Coherence Tomography

• OCT • OCT

– Optical equivalent of B-scan ultrasonography

(13)

3.4 mm Diameter

(14)

Recent Developments in OCT

• OCT is an evolving technology • OCT is an evolving technology

Spectral Domain OCT

• Uses spectroscopy rather than time • Uses spectroscopy rather than time

delay to detect depth information • Dramatically reduces scan time

(15)

Wollstein G, et al. Ophthalmology 2005; 112:229-237

(16)

Spectralis OCT (Heidelberg)

SD-OCT vs. Stratus OCT

• Fewer artifacts • Fewer artifacts

– Ho et al., Ophthalmology 2009; 116:1960-1970

• Better reproducibility

– Cirrus: Leung C, et al. Ophthalmology 2009; 116:1257-1253

(17)

SD-OCT vs. Stratus OCT

• Better sensitivity/specificity in detecting • Better sensitivity/specificity in detecting

perimetric glaucoma

– Chang RT, et al. Ophthalmology 2009; e-pub ahead of print.

• Similar sensitivity/specificity in detecting perimetric glaucoma

– Jeoung JW, Park KH. IOVS; 2009: e-pub ahead of print.

SD-OCT vs. Stratus OCT

• Principal advantages are improved • Principal advantages are improved

reproducibility

– Easier to detect progression

• Ability to measure RNFL thickness in entire peripapillary retinap p p y

– High scan speed

• Better progression software still needed on all SD-OCT devices

(18)

How can new imaging technologies

How can new imaging technologies

influence clinical practice?

Problems in Early Detection

• IOP • IOP

– Diurnal variation – Corneal thickness

– Variable sensitivity to IOP-related damage

• Inter-individual variability of optic disksy p

(19)

Problems in Early Detection

• Visual Fields • Visual Fields

– High degree of variability, even in reliable patients

– Many patients are not so reliable

Problems in Early Detection

• Suspicious vs definitive findings • Suspicious vs. definitive findings

(20)

Imaging and Glaucoma

• Provides another parameter to increase • Provides another parameter to increase

or decrease suspicion of glaucoma (or glaucoma progression)

Imaging and Glaucoma

• Don’t over react

• Don t over react – Imaging abnormality

in isolation is not enough to diagnose glaucoma

• Look for image quality and artifact

(21)

Imaging and Glaucoma

• Useful in clinical practice in conjunction • Useful in clinical practice in conjunction

with clinical exam and visual fields • Cannot interpret results of imaging in

isolation

Imaging and Glaucoma

• Each instrument has its advantages and • Each instrument has its advantages and

disadvantages

• No instrument proven to be clinically superior to others

• Initial studies suggest superiorInitial studies suggest superior reproducibility and diagnostic

performance of SD-OCT over Stratus-OCT

(22)

Evolving Technology

• HRT and GDx are nearing maturity • HRT and GDx are nearing maturity • OCT has potential for significant

improvement

– Scan speed – Resolution

Evolving Technology

• Improved software for detection of • Improved software for detection of

optic nerve abnormality and glaucoma progression needed to take advantage of higher resolution of SD-OCT

– Numerous manufacturers in the market f

References

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