Optical coherence tomography (OCT) has advanced considerably since it was first applied to the eye. It is an extension of a technique called low-coherence interferometry, which was initially applied to ophthalmology for in vivo measurements of eye axial length.
At the time of introduction, it was used to obtain in vivo optical cross sections of the anterior segment, as well as retinal diseases, such as macular detachment, macular hole, epiretinal membrane, macular edema, and idiopathic central serous chorioretinopathy.
Scan patterns that enabled reproducible measurements were developed, and these eventually became incorporated into a commercial system, which had an axial resolution of ∼10 μm.
OCT has attracted the attention of scientists working from the photonics field, out of a variety of techniques such as scanning laser polarimetry and confocal scanning laser ophthalmoscopy, because it is able to image and quantify microscopic details with high resolution.
The unique features of OCT make it a powerful imaging modality, which offers the greatest promise of delivering many fundamental research and clinical applications. OCT had the most significant clinical impact in ophthalmology.
OCT can provide quantitative information on retinal pathology and monitor disease progression in vivo that can’t be obtained by any other method. Also, OCT can detect and diagnose early stages of disease before physical symptoms and irreversible vision loss to occur.
Optical coherence tomography (OCT) is regarded as a standard diagnostic technique in various ophthalmology subdisciplines. It is essential for diagnosing blinding diseases such as macular degeneration, glaucoma, and diabetic retinopathy at early, treatable stages before irreversible loss of vision occurs.
In a similar way to ultrasound, OCT measures the “time of flight” distribution of light that is reflected from tissue and is based on low-coherence interferometry, typically using near-infrared light because the relatively long wavelength allows it to penetrate the scattering medium.
The first 2-dimensional picture of the fundus of a human eye in vivo was created by the late Adolf Friedrich Fercher in 1990 using white light interferometry. He presented his results at the International Commission for Optics Congress that year.
In 1975, he became a professor at the University of Essen, Germany; from 1986 he was professor of medical physics, and later chair of the Department of Medical Physics, at the Medical School of the University of Vienna.
He retired in 2008. Fercher published his first paper on the biomedical applications of optics while he was still working for Carl Zeiss, applying Mie theory to calculate light scattering in a simplified model cell.
He showed that the scattered signal oscillates as a function of scattering angle and that the oscillation length is related to particle diameter.
Their focus was on the eye. Although the image quality of Fercher’s 2D interferometric depth scans of the fundus was poor compared with modern standards, the retinal thickness, the excavation of the optic disc, and the lamina cribrosa were visible.
Next, David Huang, MD, PhD, and colleagues from a group led by James Fujimoto, PhD, at Massachusetts Institute of Technology, were the first to synthesize optical A-scans to 2D images (B-scans), demonstrating the potential of this technology to record cross-sectional images of translucent and scattering tissue.
Huang named this new diagnostic technique "optical coherence tomography". The first commercially available OCT device went on to be launched by Humphrey Instruments in 1996.
The technology has contributed to an understanding of disease mechanisms and treatments, including “in vivo histology” and intraoperative monitoring in disciplines including ophthalmology, cardiology, and cancer.