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Optical coherence tomography (OCT), developed in the early 1990's, has become a prominent biomedical tissue imaging technique because of its micrometer resolution and cross sectional imaging capabilities. OCT allows extremely high quality, micrometer resolution, 3-D images of biological tissues through optical signal acquisition and processing. As opposed to confocal microscopy, OCT uses near infrared light and is able to penetrate about 3 times as deep into the scattering medium.
OCT is based on low coherence interferometry, as opposed to laser interferometry that uses long coherence lengths and has the disadvantage of interference of light occurring over meters. With OCT, the interference is shortened to a distance of micrometers.
Many new applications have surfaced with the use of OCT, some of them discussed below.
Glaucoma Applications:
Tan et al conducted a study mapping ganglion cell complex thickness with high-speed Fourier-domain OCT in order to compute novel macular parameters for glaucoma diagnosis. What they found was that the higher speed and resolution of FD-OCT improved the repeatability of macular imaging compared with standard TD-OCT lending to the thought that FD-OCT can be a useful method for glaucoma diagnosis and progression tracking.
Moreno-Montanes et al compared retinal nerve fiber layer thickness using Stratus OCT-3 (OCT-3) and Heidelberg Retinal Tomograph-III (HRT-III). They found the sensitivity of RNFL damage detection using HRT-III was lower compared with OCT-3, especially in early glaucoma.
OCT has the potential to detect optic nerve damage and atrophy much earlier than previously used technology.
Anterior Segment Applications:
Jungwirth et al studied the use of full-range complex spectral domain OCT for extended in vivo anterior eye-segment imaging. With the full-range complex (FRC) technique, OCT-intrinsic depth range was doubled and the group was able to image the anterior segment from the cornea to the posterior surface of the lens with a depth range of 7mm in air. With the high sensitivity and high speed of their instrument, the anterior segment was imaged with a recording time of ~100 ms per B scan at an A scan rate of 20 kHz. Possible clinical applications of this system would be in cataract and glaucoma diagnostics, such as for imaging the anterior chamber angle, and for accommodation studies.
Perez-Rico et al described a case where Visante OCT aided in the diagnosis of pigment dispersion syndrome by demonstrating annular pigment of the posterior lens capsule and detachment of the anterior hyaloid face.
Posterior Segment Applications:
Both spectral domain OCT and time domain OCT have been used to show details of optic nerve melanocytomas such as higher reflectivity and focal thickening of the retinal pigment epithelium layer with optical shadowing. These unique OCT characteristics may help evaluate, follow and determine the prognosis for patients with these benign tumors.
As well, OCT can be used to follow patients with pseudotumor cerebri by imaging the degree of optic nerve swelling and contributing to an objective measurement of this edema. This technologic application could show promise in early disease detection and prevention of visual loss.
New advances using OCT in patients with age related macular degeneration are aimed at predicting visual loss and ultimately slowing the progression of the disease. Imaging capabilities of early disease may help physicians treat the condition and stop the process before serious visual loss occurs.
Pediatric Ophthalmology Applications:
OCT offers advantages for the pediatric population who often times cannot sit still long enough for a visual field test. The disadvantage is that normal values for children have not been established. Drs. El-Dairi and Freedman from Duke University are working to develop a normative database of healthy children. OCT for children has been used to objectively monitor children with glaucoma. It can also be used as an aid in diagnosis of optic neuropathy by showing abnormalities of the nerve when obtaining a visual field test is not reasonable. Another advantage of spectral domain OCT is that some of the devices are hand-held so can be taken directly to a baby in a nursery. Not only does this help for diagnosis of disease such as retinopathy of prematurity, but also can be used to track the changing characteristics of the growing eye.
The development of OCT in the 1990's has been revolutionary in the field of ophthalmology. New advances in this technology continue to surface, aiding the physicians in diagnosis, treatment and prevention of multiple disease processes, now even expanding outside the scope of eye disease.
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When considering your optical coherence tomography (OCT) purchase or usages, please confirm the approved medical applications of the OCT with the manufacturer.