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A coherent interpretation of OCT

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Angelica Ly
BOptom(Hons) GradCertOcTher
Senior Staff Optometrist, PhD candidate, Centre for Eye Health NSW

 

Optical coherence tomography (OCT) has emerged in a short 26 years to become a mainstay of optometric practice.

The technology has been heralded as a revolutionary and indispensable adjunct to clinical practice, profoundly advancing our ability to recognise, monitor and manage ocular diseases, especially subtle conditions. As a reflection of its clinical value, the ability to use and interpret results from OCT is now an entry-level optometric competency standard.1

Fundamentally, OCT is a diagnostic imaging technology that provides cross-sectional, in vivo imaging of ocular tissues using low coherence interferometry.2-4 It has been likened to an optical biopsy and is non-invasive, efficient even in a clinical context and utilises infrared wavelength light, so may be performed undilated. A high resolution, high density scan of the macula is typically acquired in seconds, through pupils as small as 2 mm diameter, with an optical axial resolution approximating 5 µm.

Modern instruments also carry improved sensitivity and signal-to-noise over predecessor technologies, allowing for better clarity and visualisation of previously invisible interfaces, such as the vitreoretinal interface or choroid sclera junction.5

 

Step-by-Step Guide to OCT Interpretation

 

OCT has revolutionised our understanding of ocular disease and provides unparalleled insight into macular health. The technology is best utilised through a combination of deliberate practice, an applied understanding of normal and ocular disease and anatomy, a systematic approach to the interpretation of images and an awareness of the instrument’s limitations. Lesions identified on any OCT B-scan may be co-localised against the accompanying fundus image source,6 typically a fundus photograph or infrared image (line scanning laser image, scanning laser ophthalmoscopy image or summed voxel projection) and should be considered in the context of the overall clinical presentation.

The step-by-step guide will provide an overview of how to interpret OCT in macular disease and is accompanied by a sample atlas of common macular presentations. It has been designed as a pull-out chairside reference to support the busy clinician in practice and is brought to you by the Centre for Eye Health.

Acknowledgement

The author thanks Michael Yapp and Paula Katalinic for reviewing the material.

1. Kiely PM, Slater J. Optometry Australia Entry-level Competency Standards for Optometry 2014. Clin Exp Optom 2015; 98: 65-89.

2.  Huang D, Swanson EA, Lin CP et al. Optical coherence tomography. Science 1991; 254: 1178-1181.

3.  Thomas D, Duguid G. Optical coherence tomography: a review of the principles and contemporary uses in retinal investigation. Eye (Lond) 2004; 18: 561-570.

4.  Coscas G. Optical coherence tomography in age-related macular degeneration: OCT in AMD: Springer Science & Business Media, 2009.

5.  Staurenghi G, Sadda S, Chakravarthy U, Spaide RF, International Nomenclature for Optical Coherence Tomography. Proposed lexicon for anatomic landmarks in normal posterior segment spectral-domain optical coherence tomography: the IN*OCT consensus. Ophthalmology 2014; 121: 1572-1578.

6.  Helb HM, Charbel Issa P, Fleckenstein M et al. Clinical evaluation of simultaneous confocal scanning laser ophthalmoscopy imaging combined with high-resolution, spectral-domain optical coherence tomography. Acta Ophthalmol 2010; 88: 842-849.

7.  Brar M, Bartsch DU, Nigam N et al. Colour versus grey-scale display of images on high-resolution spectral OCT. Br J Ophthalmol 2009; 93: 597-602.

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