Optical coherence tomography (OCT) was first applied to the human eye in the early 1990's. Since then, it has revolutionized ophthalmology and has become a powerful tool in studying the living human retina. OCT can be thought of as the optical analog of ultrasound. OCT is based on low coherence interferometry and typically utilizes broad bandwidth, infrared super luminescent diodes to image the retina. Light is sent into a sample arm (the eye) and a reference arm. Light reflected back from the eye is combined with light reflected from the reference arm - as the reflectivity of the tissue varies, so will the interference pattern, and this is what is analyzed within the OCT system. OCT systems provide excellent axial resolution, and enable visualization of the various layers of the retina as seen in the image here.
Bioptigen hand-held Envisu SDOIS for pediatric imaging.
There are numerous commercially-available OCT systems, each offering different functionality. The AOIP has access to 3 Spectralis® OCT systems from Heidelberg Engineering, 2 EnvisuTM Spectral Domain Ophthalmic Imaging Systems from Bioptigen, a Cirrus HD-OCT 5000 from Carl Zeiss Meditec, and an OPKO OCT/SLO system.
Whether it is an infant in the pediatric NICU at risk for retinopathy of prematurity, a child undergoing an exam under anesthesia for a retinolblastoma screening, a patient undergoing macular hole surgery in the operating room, or a middle-aged patient with early age-related macular degeneration (AMD), OCT is critical technology for the diagnosing and managing of ocular disease. By investing in a diverse portfolio of OCT technology, we enable the broadest access possible for our patients and research subjects.
Histological image (Top, courtesy Jan Provis, Australian National University) compared to an OCT image from a 32-week old infant (Bottom). The same basic anatomical features can be appreciated in both images, though it is important to note that the OCT image was acquired non-invasively from an awake infant using our hand-held imaging tools. The horizontal scale bars are 250 microns each.
One of the features of clinical OCT devices is their ability to automatically derive topographical maps of retinal thickness. The new Cirrus HD-OCT 5000 has on-board retinal tracking, which allows for repeated imaging of exactly the same retinal area from visit to visit. Shown below is the Cirrus HD-OCT 5000 system in the AOIP along with a retinal thickness map from a patient with a macular hole.
As we have with our adaptive optics imaging tools, we have used OCT to make a number of important discoveries related to the understanding of eye disease and that illustrate the utility of OCT imaging. Some examples are:
The use of hand-held OCT technology to clarify the retinal pathology in shaken baby syndrome and identify the extent of fluid/blood within and on top of the retina. This could provide a vital tool with which to examine these patients and more completely characterize the extent of retinal damage than is possible by visual exam alone. See the paper by Koozekenani et al here.
In collaboration with Dr. Brandon Lujan, Dr. Austin Roorda, and Dr. Robert Knighton, the discovery of a method to visualize a "hidden" layer within the outer nuclear layer - named the Henle Fiber Layer. See the paper by Lujan et al here.
The development of a method to mathematically characterize the size and shape of the foveal pit. Later work revealed enormous "normal" variation in this structure that was previously unrecognized. Current work is focusing on understanding the cause and consequence of this variability. See the papers by Dubis et al here and Wagner-Schuman et al here.
To see more examples from our OCT imaging efforts, please visit our Image Gallery.