OPTICAL COHERENCE TOMOGRAPHY in Glaucoma

Presented by A. Rismanchian MD Farabi Hospital Clinical Aspects Of OPTICAL COHERENCE TOMOGRAPHY IN GLAUCOMA

1Anatomy 101 for Regional ManagersOptical 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).

2ResolutionConventional ultrasound: 150 mic UBM 20 mic (penetration depth of 4 mm) CTS and MRI several hundred mic

OCT I, II : 12-15 micOCT III : 8-10 micUltra- High resolution OCT : 2-3 mic

3The operation of OCT is based on the principle of low coherence interferometry

4Light is directed onto a partially reflecting mirror and is split into reference and measurement beams.

5The measurement beam is reflected from the eye with minutely different time delays depending on its internal microstructure..

6The light in the reference beam is reflected from the mirror at a variable distance that produces a variable but known time delay.

7The light from the eye, consisting of multiple echoes, and the light from the reference mirror, consisting of a single echo with a known delay are combined and detected.

8When the two light beams coincide, they produce a phenomenon known as interference, which is measured by a photodetector.

9Retina - Histology

Ganglion CellRetinal Pigment Epithelium (RPE)INLONL (PR)Nerve fiber layerIPL-OPL-PR OS-Choroid-Chorio- capillaris-Large choroidal vessels

Tissues with high reflectivity => white or red (RPE, NFL)Those with low reflectivity => blue or green (choroid, gang cells, photoreceptors)No reflectivity : black ( vitreous)

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Retina - Histology

RNFLRPEGanglion Cell BodiesPhoto Receptors

OCT3 ImagesIn 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 GlaucomaNFL thickness in the peripapillary region circular (3.4mm) linear tomogram Optic nerve head profileMacular volume (has a reverse correlation with glaucoma damage)

14Other Clinical applicationsCorneal 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.

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NFL thickness

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Retinal Nerve FiberLayer Analysis

Circular scans of 3.4 mm measures RNFL in the peripapillary region

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Stratus OCT PrintoutRNFL Thickness Average Analysis RNFL 3.4 mm

18Patient information scan information

19Fundus ImageTo verify scan placement.

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