Presented by A. Rismanchian MD Farabi Hospital Clinical Aspects
Of OPTICAL COHERENCE TOMOGRAPHY IN GLAUCOMA
Slide 3
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).
Slide 4
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
Slide 5
The operation of OCT is based on the principle of low coherence
interferometry
Slide 6
Light is directed onto a partially reflecting mirror and is
split into reference and measurement beams.
Slide 7
The measurement beam is reflected from the eye with minutely
different time delays depending on its internal
microstructure..
Slide 8
The light in the reference beam is reflected from the mirror at
a variable distance that produces a variable but known time
delay.
Slide 9
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.
Slide 10
When the two light beams coincide, they produce a phenomenon
known as interference, which is measured by a photodetector.
Slide 11
Retina - Histology Ganglion Cell Retinal Pigment Epithelium
(RPE) INL ONL (PR) Nerve fiber layer IPL- 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)
OCT3 Images In previous OCT images, we were able to see four
layers of the retina. Now we are seeing 7, or sometimes 8.
Slide 14
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.
Slide 15
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)
Slide 16
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.
Slide 17
NFL thickness
Slide 18
Retinal Nerve Fiber Layer Analysis Circular scans of 3.4 mm
measures RNFL in the peripapillary region
Slide 19
Stratus OCT Printout RNFL Thickness Average Analysis RNFL 3.4
mm
