Optical coherence tomography (OCT) is a non-invasive procedure that uses a diode laser to examine intraocular structures and create cross-sectional and three-dimensional images of the retina. It can detect anatomical changes in eye structures and provide valuable information about structural abnormalities, such as subretinal tumors and macular holes. However, obstacles to achieving satisfactory OCT scans include opacity of the cornea or lens, lack of patient compliance, and excessive blinking.
Optical coherence tomography (OCT) is a procedure used for the non-invasive examination of intraocular structures. Primarily used for analysis of the retina and optic nerve, OCT focuses on the amount of light absorption or scattering that occurs when light passes through a given layer of tissue. Optical coherence tomography uses a diode laser, which emits light at a wavelength of about 840 nanometers. Two beams of light are compared, measured and analyzed, a reference beam aimed at a mirror and a detection beam aimed at eye tissue. OCT allows doctors to develop cross-sectional images of the anterior chamber of the eye and three-dimensional images of the retina.
OCT images allow doctors to detect anatomical changes in eye structures that occur with glaucoma and retinal diseases. Ophthalmologists can determine the overall retinal thickness and the thickness of individual layers of the retina to identify macular swelling, macular degeneration, and macular holes. They can easily recognize the epiretinal membranes on the retinal surface. In addition, optical coherence tomography facilitates the assessment of horizontal and vertical cup dimensions relative to the disc for long-term monitoring of glaucoma damage.
Obstacles to achieving satisfactory optical coherence tomography scans include opacity of the cornea or lens, lack of patient compliance, and excessive blinking. The OCT device achieves approximately 27,000 scans per second, allowing for greater resolution and detail with minimal time required. While it is possible to get high-quality scans through a small pupil, sometimes the pupils need to be dilated. It is also helpful for the patient to use artificial lubricants on the surface of the eye before the exam.
Optical coherence tomography examination often provides valuable information about structural abnormalities. For example, subretinal tumors, such as melanomas, can lift the entire retina, producing an upward bow of the retina visible on OCT. An epiretinal membrane will appear as a bright line overlying the retina with wavy folds below the line, due to lateral pulling on the retinal surface by the membrane. A full thickness macular hole will appear as a clear discontinuity in the retina at the macula with pockets of fluid in the adjacent retina.
Additionally, OCT scans offer useful insights into changes in the pattern of light reflection from a tissue. High light reflectivity can occur with choroidal nevus, a mole-like structure deep in the retina, due to the brown pigment within it. The scar tissue will also be highly reflective. Conversely, fluid pockets, such as cysts or detachments, will appear dark on the scan. The degree of reflectivity depends on the depth of the fabric, the composition of the fabric and the orientation of the fabric. Horizontal structures tend to be more reflective than vertically oriented structures.
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