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Chapter-10 Optical Coherence Tomography

BOOK TITLE: Uveitis: Text and Imaging

Author
1. Gupta Amod
2. Gupta Vishali
3. Velthoven Mirjam EJ van
4. Garcia Patricia MT
5. Rosen Richard B
6. deSmet Marc D
ISBN
9788184484915
DOI
10.5005/jp/books/11002_10
Edition
1/e
Publishing Year
2009
Pages
43
Author Affiliations
1. Advanced Eye Centre, Postgraduate Institute of Medical, Education and Research, Chandigarh, India, Postgraduate Institute of Medical, Education and Research, Chandigarh, India
2. Advanced Eye Centre, Postgraduate Institute of Medical Education and Research, Chandigarh (India), King Khaled Eye Specialist Hospital, Riyadh, KSA, Postgraduate Institute of Medical, Education and Research, Chandigarh, India, Postgraduate Institute of Medical, Education and Research (PGIMER), Chandigarh, India
3. Academic Medical Centre, Amsterdam, The Netherlands
4. New York Eye and Ear Infirmary, New York, USA
5. New York Eye and Ear Infirmary, New York, USA
6. University of Amsterdam The Netherlands Vitreo-retinal and Uveitis Services, ZNA Middelheim Campus, Antwerp, Belgium
Chapter keywords
optical coherence tomography, tomographic cross-sectional image, fundus photography, indocyanine green angiography, haemorrhage, retinal oedema, choroidal rupture scars, disciform scars, neurosensory retina, inflammatory lesion

Abstract

This chapter provides an overview of optical coherence tomography, which gives a tomographic crosssectional image of the retina, RPE-choriocapillaris in the axial direction, that complements the standard topographic imaging techniques like fundus photography, fluorescein and indocyanine green angiography. The principle of OCT is essentially similar to ultrasound B-scan, except light (low-coherence) is used instead of sound. The images are obtained by measuring the time delay of the light rays from different microstructures in the eye. A beam splitter is placed in front of the light source that is emitting a continuous beam of low-coherence light. The machine hardware essentially consists of a patient module with a chin rest, focus adjustment knob, joystick and a computer unit with a flat screen video monitor, keyboard, mouse and printer. The hardware mounts on a motorised table. It is preferable to dilate pupil before examination as small pupils of less than 3 mm may result in images that are truncated or are of poor quality due to lack of image intensity. The hard exudates are seen as hyper-reflective shadows in the neurosensory retina that completely block the reflections from the underlying retina. Blood causes increased scattering. In cases of small and thin haemorrhage, hyper-reflectivity is seen, whereas if the haemorrhage is thick, it might block the reflections from the underlying structures. All the fibrotic lesions including disciform scars, choroidal rupture scars, healed choroiditis, etc. are hyper-reflective. Retinal oedema is the commonest cause of reduced backscattering and one can localise the site of fluid accumulation. The serous fluid that is devoid of any particulate matter produces an optically empty space with no backscattering. OCT is able to define the extent, depth and thickness of the inflammatory lesion. It helps to localize the level of retina-choroid harbouring the lesion. This localisation is helpful in not only diagnosing the disease but also in monitoring the response to treatment.

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