For instance, while the Spectralis OCT has an eye tracking feature, the scanning time may be longer than some of the other devices’ times. Therefore, it’s important to be aware of device differences when assessing for progression.Įach of the three SD-OCT devices we’ve worked with has its own benefits and drawbacks. On the other hand, each device has developed its own normative database, which aids in interpretation of scans. 4 This could lead to misdiagnosis of glaucoma progression if a patient was imaged initially on an RTVue device but subsequently imaged with any other device. For example, it’s been shown that RTVue gives a thicker peripapillary retinal nerve fiber layer thickness reading in comparison to the other two. Another swept-source OCT device, the Plex Elite 9000 from Zeiss, is available, but primarily for research purposes, as opposed to common clinical practice for glaucoma.Īs was mentioned earlier, in terms of commonly used devices, there are some differences to be aware of. While this type of scan may offer an advantage over SD-OCT in detecting glaucoma progression, its clinical utility has yet to be proven in large, prospective studies. This device images the peripapillary RNFL and inner retinal thickness in the macula in one wide-angle scan. In addition to SD-OCT devices, swept-source OCT, such as the DRI Triton (Topcon Corporation, Tokyo, Japan), is commercially available. Some of their specifications and differences are summarized in Table 1 (pg. The OCT devices we work with are the Cirrus HD-OCT (Carl Zeiss Meditec Dublin, California), Spectralis (Heidelberg Engineering Heidelberg, Germany), and RTVue-100 (Optovue Fremont, California) we’ll refer to them throughout the article. Spectral-domain units are made by several manufacturers the devices differ in scanning protocols and segmentation algorithms, so their measurements are not easily interchangeable. 3 With side by side comparison, they were able to show that the reflectance patterns imaged by SD-OCT corresponded precisely to the various retinal layers.Ĭurrently, SD-OCT is the OCT device most commonly used in clinical practice. The correlation between anatomic structures and volumetric spectral domain-OCT images of the optic nerve head was made clear in a study by Nicholas Strouthidis, MD, and his colleagues at Devers Eye Institute, Oregon, when they performed SD-OCT imaging of the optic nerve head in monkeys and obtained thin histological sections of the same tissues. 2 In addition to cupping of the optic nerve, glaucoma patients often show sectorial loss of nerve fiber layer, which can be visualized with a red-free light. 1 In addition, the connective tissue in the ONH undergoes profound remodeling in glaucoma, leading to posterior deformation of the lamina cribrosa as well as expansion of anterior and posterior neural canal openings, as illustrated in an experimental monkey model of glaucoma. Green, MD, demonstrated that the increased optic disc cup size was caused by the loss of retinal ganglion cells and their axons. In 1979, Harry Quigley, MD, and William R. The axons exit the eye through the neural canal opening and are supported by the lamina cribrosa (essentially a connective tissue structure), which comprises the floor of the physiologic cup. The ONH is formed by the axons of the retinal ganglion cells, blood vessels and glial tissue. Glaucoma is characterized by loss of retinal ganglion cells and their axons, and by the remodeling of the optic nerve head, which manifests as neuroretinal rim narrowing, optic disc excavation and displacement of lamina cribrosa. Therefore, we’ll discuss the various tissue structures affected by glaucoma progression and then provide practical tips for using OCT to monitor them. One major advantage of OCT is its ability to show detailed, quantitative information about the various retinal layers, which corresponds to tissue sections on a histology slide. In this article, we’ll provide tips on how to use the OCT devices we’re familiar with to monitor progression, and how to avoid artifacts and other errors that can lead you astray. Although these remain key elements of the glaucoma evaluation, they’re still subjective and qualitative in nature, limiting their ability to detect progression reliably. Before the introduction of optical coherence tomography, determination of glaucoma progression relied heavily on clinical assessment of the optic nerve, comparison of disc photos over time and visual field analysis. S ince glaucoma is a progressive disease, physicians are constantly searching for reliable tools to monitor it over time.
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