OCT-C key terms

A measurement technique that splits light into two paths and recombines it so the waves overlap, producing a signal that reveals how far away and how reflective structures are along the beam.

A light source that emits a broad range of wavelengths, so its waves stay in step over only a very short distance; this short overlap is what gives OCT its fine depth resolution.

The short distance over which the waves from a broadband light source remain sufficiently in step to interfere; it sets the axial resolution of an OCT system, with shorter values giving finer resolution.

The light path inside the instrument that travels to a mirror and back without entering the eye; matching its length to the light returning from tissue selects which depth is being imaged.

The smallest separation, measured along the direction of the beam, at which two reflective surfaces can still be told apart; in OCT it depends mainly on the bandwidth of the light source.

A single depth profile taken along one line through tissue, plotting reflection strength against depth; many of these placed side by side form a cross-sectional image.

A two-dimensional cross-sectional image assembled from many adjacent depth profiles, showing the retina from the side with depth on one axis and position on the other.

A method that uses a spectrometer to record all depth information at once as a spectrum, then applies a mathematical transform to create depth profiles; it images far faster than older time-domain systems.

A method in which a laser rapidly tunes through a range of wavelengths while a detector records the interference signal; the longer wavelengths used allow deeper imaging into the choroid and optic nerve.

A pattern of parallel, evenly spaced lines covering a rectangular area, used to build volume scans of the macula or optic nerve head for measurement and review.

A pattern in which the beam traces a ring around a chosen structure, most often the optic disc, so that peripapillary retinal nerve fiber layer thickness can be measured.

Positioning the scan pattern so that its center matches the structure of interest, such as the fovea or disc center, so that measurements are taken at the intended anatomic location.

Changing the instrument's optical focus so the beam is sharpest at the retinal layer of interest; poor focus lowers signal strength and blurs fine detail in the image.

The innermost boundary of the retina, formed by the footplates of Müller cells; on a B-scan it appears as the first bright line on the vitreous side.

The layer of ganglion cell axons that run along the inner retina toward the optic disc; it is highly reflective on OCT and its thickness is measured when evaluating glaucoma.

A bright band on OCT that marks the inner segment ellipsoid region of the photoreceptors; loss or disruption of this band suggests photoreceptor damage and predicts visual outcome.

A single layer of pigmented cells lying between the photoreceptors and Bruch membrane; it forms a dense, highly reflective band on OCT and serves as a boundary for many measurements.

A thin, layered sheet between the retinal pigment epithelium and the choroid; on a scan it appears as the reflective line immediately beneath the pigment epithelium band.

The vascular layer between Bruch membrane and the sclera; on OCT it appears as a mottled band beneath the pigment epithelium, and its thickness and vessel pattern are assessed in many diseases.

The small dip in the inner retinal surface at the center of the macula where the inner layers are pushed aside; its normal contour helps confirm that a scan is properly centered.

The site where retinal nerve fibers leave the eye; on OCT it shows a surface contour, prelaminar neural tissue, and the lamina cribrosa, and it is imaged when assessing glaucoma.

The back surface of the vitreous gel that rests against the inner retina; it is usually invisible on OCT unless it separates, when it appears as a faint reflective line.

A device-reported number or bar showing how much light returned from the tissue; low values warn that the scan may be unreliable and should be repeated before measurements are trusted.

Distortion caused by eye or head movement during scanning, appearing as doubled lines, steps, or gaps between adjacent slices; it can imitate disease or corrupt thickness measurements.

Loss of signal beneath a structure that blocks or scatters light, such as dense hemorrhage or a large vessel, so the tissue below appears dark and cannot be interpreted.

A false image folded to the wrong side of the zero-delay point when a structure lies outside the imaging range or returns too much light, duplicating real tissue in an impossible location.

Failure of automated software to place a boundary line on the correct layer, often because of weak signal or pathology; it yields wrong thickness values even when the image looks acceptable.

Deposits of material beneath the retinal pigment epithelium that appear as dome-shaped elevations of the pigment epithelium band, often with a matching bump of the ellipsoid zone above.

Abnormal fluid located within the retinal layers, seen as dark round or oval spaces inside the retina; it is a common sign of macular edema from many different causes.

Fluid that collects between the photoreceptors and the retinal pigment epithelium, appearing as a dark space lifting the retina away from the underlying band.

A sheet of fibrous tissue growing on the inner retinal surface, seen as a bright line above the internal limiting membrane that may wrinkle the retina and distort the foveal contour.

Persistent pulling on the macula by a posterior hyaloid that has only partly detached, seen as a focal attachment with distortion of the underlying retinal contour.

Separation of the retinal pigment epithelium from Bruch membrane, seen as a dome-shaped elevation of the pigment epithelium band with material of varying reflectivity beneath it.

Measurement of corneal thickness with OCT, performed by scanning across the cornea and measuring the distance between the epithelial surface and the endothelial surface.

The junction between the cornea and the iris where aqueous humor drains; anterior segment OCT can image this region to judge whether the angle is open or narrow.

The upper limit of light energy a patient's eye may safely receive for a given wavelength and exposure time, defined by the recognized laser safety standard ANSI Z136.1.

Infection-control practices applied to every patient, including hand hygiene, gloves where indicated, and cleaning or disinfecting devices that contact the eye or tears.