Clinical Aspects Of OPTICAL COHERENCE TOMOGRAPHY IN GLAUCOMA

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

Optical coherence tomography (OCT; Zeiss-Humphrey) n n 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).

Resolution n n n 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

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

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

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

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

n The 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.

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

Tissues with high reflectivity => white or red (RPE, NFL) Those with low reflectivity => blue or green (choroid, gang cells, photoreceptors) No reflectivity : black ( vitreous) Retina - Histology Nerve fiber layer IPLOPLPR OSChoroid -Choriocapillaris -Large choroidal vessels Ganglion Cell INL ONL (PR) Retinal Pigment Epithelium (RPE)

RNFLRetina - Histology Ganglion Cell Bodies Photo Receptors RPE

OCT 3 Images In previous OCT images, we were able to see four layers of the retina. Now we are seeing 7, or sometimes 8.

We Now Believe That the Best Way to View OCT 3 Images is in the B & W Mode. It Appears to Give More Details. OCT 3 Images

Types of measurment in Glaucoma n n n NFL thickness in the peripapillary region circular (3. 4 mm) linear tomogram Optic nerve head profile Macular volume (has a reverse correlation with glaucoma damage)

Other Clinical applications n n n 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 Fiber Layer Analysis Circular scans of 3. 4 mm measures RNFL in the peripapillary region

Stratus OCT Printout RNFL Thickness Average Analysis RNFL 3. 4 mm

Patient information scan information n

Fundus Image To verify scan placement. n