Optical coherence tomography--a review of the principles and contemporary uses in retinal investigation

Eye (2004) 18, 561570

& 2004 Nature Publishing Group All rights reserved 0950-222X/04 $30.00www.nature.com/eyeOptical coherence

tomographyFa

review of the

principles and

contemporary uses

in retinal

investigationREVIEWD Thomas1 and G Duguid2Eye (2004) 18, 561570. doi:10.1038/sj.eye.6700729Published online 6 February 2004IntroductionOne of the most exciting developments inophthalmic imaging in recent years is opticalcoherence tomography (OCT). This techniquepicks up where the resolution of ultrasoundleaves off, offering an entirely new spectrum ofhigh-resolution, cross-sectional images of theretina, vitreous, choroid, and optic nerve.1Imaging of the anterior segment is alsopossible.24 In the posterior segment, OCT isevolving as a noninvasive investigation in theplace of, or complementary to, fluoresceinangiography. This article aims to give the readeran understanding of the principles involved inOCT, an overview of the appearances of thecommonly encountered conditions, and adescription of the contemporary uses for OCT inretinal investigation. There are currently only afew OCT machines installed in the UnitedKingdom, but with increasing awareness of thepotential benefits of OCT imaging, cliniciansshould be able to refer patients for imaging at alocal centre and then manage their own patientson the resulting diagnosis or measurement.1St Thomas Hospital

Lambeth Palace Road

London, UK2The Western Eye Hospital

Marylebone Road

London, UKCorrespondence: G Duguid

The Western Eye Hospital

Marylebone RoadLondon NW1 5YE, UKTel: 44 20 76167666

Fax: [phone]

E-mail: g.duguid@

thelondonclinic.co.ukPrinciplesStandard ultrasound depends on reflection ofhigh-frequency sound waves (in the order of10 MHz travelling at 1500 m/s in water) and islimited to a resolution of about 150 mm. OCTuses reflection of short coherence length light(usually 830 nm wavelength at a speed of3 108 m/s) and results in resolution in theorder of 10 mm. Although high-resolution

ultrasound systems are available allowing up to20 mm resolution, their penetration in tissue islimited to only 45 mm. The clear media of theeye has lent itself to noncontact, noninvasiveimaging by OCT, with imaging of other bodytissues such as trachea,5 uterus,6 bladder,7gastrointestinal tract,8 and peripheralvasculature9 requiring endoscopy to deliverlight. In these organs, it is possible to obtain anoptical biopsy of 10 mm resolution in vivo byplacing the probe adjacent to the wall of ahollow viscus,10 with obvious potential in theearly diagnosis of internal tumours.The commercially available OCT machinefrom Humphrey Instruments Ltd (San Leandro,CA, USA), was developed by a team ofbioengineers and ophthalmologists at theMassachusetts Institute of Technology,11 and iscurrently the only machine in...