Optical Coherence Tomography (OCT)

Gella Laxmi2009PHXF013P

Introduction

OCT

Determining and visualizing structure that absorb and scatter light

Noninvasive in vivo analysis of retinal tissue

1 mm 1 cm 10 cm

Penetration depth (log)

1mic

10mic

100micronm

Resolution (log)

Ultrasound

OCTConfocalmicroscopy

Standardclinical

CT and MRI

Principle

Michelson Interferometer

Beam splitter

Diode 820

Reference beam

Patients eye

DVD

OCT software

Detector

Combination of multiple A scans to produce…..

Time Domain OCT

CHORIOCAPILLARISCHORIOCAPILLARIS

NFLNFLGCLGCL

FOVEOLAFOVEOLA

IPLIPL

INLINL

OPLOPL

ONLONL

RPERPE PHOTORECEPTORSPHOTORECEPTORS ELMELM

Spectral Domain OCT

Features of SD-OCT

Better anatomic representation

High resolution (6 microns)

Fewer movement artifacts

Live cross-sectional movies of various details

High Signal to noise ratio

Scanning speed 25, 000 A-scans per second

3D imaging

Vs

Histological retina Vs SD-OCT

Retinal Structures on SD-OCT

Horizontally oriented structures – hyperreflective

Vertically oriented structures (layers containing nuclei) – hypo reflective

Choriocapillaris: Innermost limit of the

vascular layer of the eye

Thin and hyper-reflective

layer

Larger vessels of choroid

– hyporeflective

Inconsistently identified

Bruch’s membrane: Not visible on SD-OCT

VV

VVV

CCRPECCRPE

V

CCRPE

Retinal Pigment Epithelium:

RPE-CC complex divided into 3 parallel strips

2 are thick, hyperreflective separated by thin

hyporeflective line

Verhoef’s membrane

Photoreceptors:

Rods and cones contain inner and

outer parts

Inner part: nuclei (outer nuclear layer)

Outer part: inner and outer segment

Connection b/w inner and outer

segment forms a hyper-reflective strip

(result of diff in RI)

Sharply raised at the foveola

External limiting membrane

Outer plexiform layer: Visual cells connect to the bipolar cells

Horizontal axons of the horizontal cells

Hyper-reflective strip

Inner nuclear layer: Nuclei of bipolar, horizontal, muller and amacrine

cells

Hyporeflective layer

Inner plexiform layer: Synapses b/w ganglion cells and amacrine cells Hyper-reflective owing to their horizontal

structure

Ganglion cell layer Bulky cells are multilayered Hyper-reflective

Nerve fiber layer Nerve axons Very high reflective layer

RNFLGCLIPL

Internal limiting membrane

Difficult to distinguish

Hyaloid and vitreous

Various pathologic structures clearly visible

Reporting SD-OCT

Comment on each layer

Reflectivity

Morphological features

Measurements of thickness

Take-home message

Retinal anatomy and virtual histology can be

studied with the SD-OCT

The SD-OCT shows more detail at the

vitreoretinal interface, and there is better

delineation of all retinal layers

References

Bruno Lumbroso. SD-OCT Reveals Details of Posterior Segment Structures. Cataract & refractive surgery today Europe. June 2008. Pg 27-28

Wolfgang Drexler, et al. State-of-the-art retinal optical coherence tomography. Progress in retina and eye research. 2008.Jan; 27(1): 45-88

Bruno Lumbroso, et al. Understanding Spectral OCT. I.N.C Innovation-News-Communication. 2007.

Michael R. Hee, et al. Optical Coherence Tomography of the Human Retina. Arch Ophthalmol. 1995; 113: 325-332.