Welcome

Presented by

Akram Rismanchyin MD

Isfahan University

2008

OCT3

Clinical Aspects Of

OPTICAL COHERENCE TOMOGRAPHY IN

GLAUCOMA

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 different

disorders 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.

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

Standard clinical techniques for assessing glaucOluatous changes, such as optic nerve head and NFL examination or visual fteld testingt lack sensitivity and reproducibility.

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

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

HRT (cslo)

Structural diagnosis GDX (sip)

OCT

Optical coherence tomography (OCT; Zeiss-Humphrey) Introduced in 1991 Provides 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).

OCT / B-Scan

Resolution Conventional ultrasound: 150 mic UBM 20 mic (penetration depth of 4 mm) CTS and MRI several hundred mic OCT I, II : 12-15 mic OCT III : 8-10 mic Ultra- High resolution OCT : 2-3 mic

Resolution

Correlation between OCT and histopathologic examination revealed agreement for RNFL thicknesses within

10 μm OCT may underestimate histological NFL

thickness by an average of 37%

(Jones et al, 2001)

The operation of OCT is based on the principle of low coherence interferometry

Light is directed onto a partially reflecting mirror and is split into reference and measurement beams.

The measurement beam is reflected from the eye with minutely different time delays depending on its internal microstructure..

When the two light beams coincide, they produce a phenomenon known as interference, which is measured by a photodetector.

Retina - HistologyRed Blue/Brown

Ganglion Cell

Retinal Pigment Epithelium (RPE)

INLONL (PR)Nerve fiber

layer

IPL-OPL-

PR OS-Choroid-Chorio- capillaris-Large choroidal

Retina - Histology

Ganglion Cell

Retinal Pigment Epithelium (RPE)

INLONL (PR)

Nerve fiber layer

IPL-OPL-

PR OS-Choroid-Chorio- capillaris-Large choroidal vessels

Retina - Histology

RNFL

RPE

Ganglion Cell Bodies

Photo Recept

ors

OCT3 Images

In previous OCT images, we were able to see four layers of the retina. Now we are

seeing 7, or sometimes 8.

OCT3 Images

We Now Believe That the Best Way to View OCT3 Images is in the B & W Mode. It

Appears to Give More Details.

Types of measurment in Glaucoma

NFL thickness in the peripapillary region

circular (3.4mm) linear tomogram

Optic nerve head profile Macular volume (has a reverse

correlation with glaucoma damage)

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.

NFL thickness

Retinal Nerve FiberLayer Analysis

Circular scans of 3.4 mm measures RNFL in the peripapillary region

Stratus OCT PrintoutRNFL Thickness Average Analysis RNFL 3.4 mm

Patient information scan information

Fundus Image

To verify scan placement.

Scan Image The image with the lowest signal strength or with a data

message will be shown to facilitate operator review.

Signal Strength

Numbers range from 0 (weak) to 10 (strong).

images with a signal strength below 5 should not be used.

Sector Averages Comparison to

normative data in each sector is indicated with stoplight color scheme.

Values are displayednumerically.

Quadrant Averages Comparison to normative

data in each quadrant isindicated with stoplight color scheme.

Values are displayednumerically.

OCT3 Analysis Program

The 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.

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

OD/OS Graph TSNIT line graph displays RNFL

thickness in both eyes. Asymmetry may be indicative of

glaucomatous loss.

Legend Normative data is displayed in stoplight

color code, described in detail on insideback cover.

Best parameters for Sratus OCT

>or=1 quadrants abnormal p<5%

>or=1 clock hours abnormal at p<5%

OCT RNFL Thickness Analysis – OU Overlay

OU Overlay

OD in Blue

OS in Green

“Normal” eyes =

Similar shape

Abnormal eyes =

Dissimilar

shape

Loss of RNFL in OS Superior “Hump” May be

an Indication of Pathology

Tabular Data For each eye, values are compared

to normative data and displayed instoplight color code, described in detailon inside back cover.

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) mean But the normal and abnormal ranges overlap

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

ABILITY TO DETECT CHANGE Change analysis software has

recently been introduced However, statistical units of change

probability are not provided It is difficult to differentiate true

physiologic change from test-retest variability.

RNFL Thickness Serial AnalysisComparative analysis of RNFL thickness over time. Can be applied to up to 4 OD and/or 4 OS scan groups

Optic Nerve Head Analysis

Objectively finds Margin of Disk using signal from end of Retina Pigment Epithelium

Not accurate on:

- Peripapilary Atrophy

- Staphyloma

Optic Nerve Head Analysis Radial line scans through optic disc provide

crosssectional information on cupping and neuroretinal rim area

Disc margins are objectively identified using signal from end of RPE

Key parameters include cup-to-disc ratio and horizontal integrated rim volume

Optic Nerve Head Analysis

Objectively finds Cup

and calculates

volumes and areas

of the ONH

User can modify

placement of

disk

Does not require

reference plane

as with other

technologies

ONH Indices

ONH measurements with OCT

Compared with ONH measurements, RNFL thickness may be a better indicator of retinal ganglion cell function and disease progression.

Macular Thickness Analysis`Thinning of the macula may reflect

glaucomatous loss

Stoplight Color Scheme

Healthy eye The anterior and posterior highly reflecting

layers (shown in red), representing the RNFL and RPE

Glaucomatous eye A broad focal defect in the superotemporal quadrant

with thinning of the RNFL to less than 50 μm.

Shows a baseline and follow-up image of an uncontrolled glaucomatous eye after a 16-month interval.

Thinning of the RNFL in the inferotemporal quadrant

Superior Arcuate Scotoma

NORMAL GLAUCOMA

OCT Advantages Noninvasive Non-contact High resolution High sensitivity Not affected by axial length and refraction Not affected by moderate nuclear sclerotic

cataracts.

Objective, quantitative, reproducible In contrast with other imaging techniques,

direct measurements of the RNFL An anterior segment compensator is

unnecessary and structural information is independent of a reference plane.

ADVANTAGES

High cost Posterior subcapsular and cortical

cataracts impairs performance Currently change analysis software

lacks statistical units of change probability, making it difficult to differentiate biological change from measurement variability.

DISADVANTAGES

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.

In Summary

It 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.