12/19/2023 0 Comments Glaucoma optical coherence tomographyTen years later, Optovue’s spectral domain (SD-OCT) scanner was the first to obtain FDA approval for clinical use. Soon after the publication of the first images of the optic disk, Humphrey instruments introduced the first commercial OCT scanner in 1996. Thus, OCT technology introduced a novel and precise method for visualizing and measuring defects in the optic nerve, retina, and nerve fiber layer. This imaging modality provides key structural information such as retinal thickness (μm), RNFL thickness (μm), and abnormal reflectivity on retinal layers which could indicate the presence of edema, exudates, calcifications, or atrophy. By comparing the reflected light to an unobstructed reference path, the location and morphology of ocular structures can be determined to generate a cross sectional image of the eye. In this technique a beam of light is shone into the eye and reflected light is captured and measured. It is a non-invasive imaging methodology for acquiring high resolution images of the retina and optic nerve using low-coherence interferometry. OCT technology was first developed at the Massachusetts Institute of Technology by David Huang in 1991 ( Figure 4). Ģ.1 The development of optical coherence tomography Thus, OCTA has addressed prior limitations of OCT and has revolutionized the evaluation of several ophthalmic diseases, including glaucoma by allowing clinicians to distinguish between glaucoma suspect, healthy, and glaucomatous eyes. Improvements in the OCT technology has led to the development of optical coherence tomography angiography (OCTA), a rapid, noninvasive imaging modality that can provide quantitative and volumetric assessment of both the structure and vascular aspects of the retinal and optic nerve. Particularly, it is extremely challenging to distinguish between differing degrees of glaucoma severity, identify patients with optic cupping who have normal vascular perfusion, as well as monitor patient response to treatment over time. While OCT has greatly improved the accuracy and consistency of glaucoma diagnosis, it is still limited since it cannot probe the vascular degradation that occurs in glaucoma. Specifically, peripapillary retinal nerve fiber layer (RNFL) analysis is widely used for glaucoma diagnosis, as RNFL thinning can indicate glaucomatous damage. Similarly, visual assessment of the optic nerve and VF testing are subject to high degrees of inter- and intra-examiner variation, limiting their abilities to diagnose and follow patients with glaucoma accurately and objectively.ĭue to these challenges, optical coherence tomography (OCT) technology has grown in popularity due to its ability to provide additional objective information about the structure and morphology of the optic nerve and retina. One key challenge is that IOP measurement is not standardized and can be affected by the central corneal thickness (CCT), type of tonometer used, time of day, as well as the skill and training of the clinical staff obtaining the measurements. However, this approach is limited by its inherent subjectivity and measurement inconsistencies. Glaucoma is diagnosed using three parameters: measurement of IOP, evaluation of the optic nerve anatomy, and VF testing. This chapter describes the role of OCTA in managing patients with glaucoma.ġ.2 Optical coherence tomography angiography addresses current challenges in glaucoma diagnosis Various researchers have shown that OCTA provides an accurate and objective evaluation of the retina and the optic nerve in glaucoma. Optical coherence tomography angiography (OCTA) is a rapid, non-invasive imaging modality that provides 3-D, volumetric details of both the structure and vascular networks of the retina and optic nerve. Current diagnostic methods, such as measuring IOP, VF testing, and ONH evaluation, are subjective and often unreliable. The two prevalent theories explaining glaucomatous damage are mechanical (elevated IOP) and vascular (compromised optic nerve perfusion). Risk factors include older age, black or Hispanic race, elevated IOP, thin central corneal thickness, disk hemorrhage, and low ocular perfusion pressure. Primary open-angle glaucoma, the most common type, is a multifactorial progressive optic nerve neurodegenerative disorder that leads to loss of optic nerve head (ONH) tissue, thinning of the retinal nerve fiber layer, and corresponding visual field (VF) defects with or without elevated intraocular pressure (IOP). Glaucoma is the second leading cause of blindness worldwide, affecting eighty million people globally and three million patients in the USA.
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