5Conventional clinical imaging technologies such as ultrasound, magnetic resonance, or computed tomography have poorer resolution compared with that achieved with this novel technology. These A-scans are then combined to form a composite, cross-sectional image (B-scan). In early generation TD OCT machines, multiple readings are produced as a reference mirror physically moves in a linear fashion over the target, creating individual A-scans that indicate a specific measure of the depth and reflectivity of the underlying tissue.
Several interference patterns are created in this fashion. 4The device creates an interference pattern by gathering reflected light beams from the target tissue and from the reference. The technology compares or correlates one optical beam of light or light wave (reference) with another as the light waves return from the variably reflective tissue layers of the eye. Imaging with OCT technology is based on the use of an optical device known as the Michelson interferometer.
CMM COHERENCE EXAMPLES SERIAL
The most important advance in OCT technology was the transition from TD OCT to SD OCT because the latter is much more efficient than the serial scanning performed by the TD OCT, discussed in detail later in this chapter. The image had an axial resolution of around 15 μm, which was almost 10 times finer than conventional clinical imaging modalities such as ultrasound. The first demonstration of OCT imaging was reported by Huang et al, 1showing a TD OCT ex vivo scan of the human retina and its corresponding histology. The purpose of this chapter is to illustrate the evolution and utilization of AS HR and UHR OCT imaging and its clinical applications, specifically in the diagnosis, differentiation, and management of ocular surface tumors.ģ.1 Optical Coherence Tomography: The Evolution to Ultrahigh-Resolution OCT 10 , 11 , 12Īs OCT technology improves, it has the potential to revolutionize the management of the ocular surface. However, UHR OCT can provide adjuvant information to a clinical diagnosis before excision, thus allowing early differentiation and management of suspicious lesions. Ocular surface squamous neoplasia (OSSN), conjunctival melanoma (CMM), and conjunctival lymphoma are conditions that require biopsy for a definitive diagnosis. Ultrahigh-resolution OCT has provided a noninvasive method to evaluate ocular surface lesions. 4 , 5 , 6 , 7 , 8These newer devices with improved axial resolution and imaging speed made possible the visualization of not only AS dystrophies and degenerations 9but also of other several ocular surface conditions, disclosing reliable images with high correlation to pathology specimens. It was not until the development of spectral-domain OCT (SD OCT) devices, capable of HR OCT imaging-down to 5 µm-and ultrahigh-resolution (UHR OCT) devices-less than 5 µm-that the ocular surface was able to be imaged to a degree that structural details of the corneal epithelium, corneal stroma, and conjunctiva were elucidated.
3These early devices provided some information regarding the AS anatomy but not the fine details of ocular surface lesions. This technology provided resolution of about 15 to 18 µm. Since its development in 1991, OCT has been used for several clinical applications, 1 , 2and even though it was initially conceived as a means of imaging the eye posterior segment, it was later used for the anterior segment (AS).Įarly OCT systems detected light echoes using what is known as time-domain (TD) detection. The eye is an optically accessible organ, and OCT technique permits high-resolution (HR) images of normal tissues and pathology. Optical coherence tomography (OCT) is a powerful imaging modality that has revolutionized the field of ophthalmology by providing real-time, in vivo, cross-sectional images of ocular tissues.
3 Ultrahigh-Resolution Optical Coherence Tomography for Imaging of Ocular Surface Tumors Juan C.
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