oct:basic consept f.fazel.md. optical coherence tomography 1995-1996 introduced in to clinical...
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OCT:BASIC CONSEPT
F.FAZEL .MD
Optical Coherence Tomography
1995-1996 introduced in to clinical practice Retina,glaucoma,anterior segment Rapid,easy,non-
contatc,noninvasive,sensitive,highly reproducible and repeatable
Qualitative and quantitative
How the OCT work
The OCT uses an interferometer that measures the time it takes for light to be reflected back from structures in the retina, as compared to the time it takes for light to be reflected back from a reference mirror at specific distances. The process is similar to that of ultrasonography, except that light is used instead of sound waves.
Retinal layer scanning
Differences of OCT and sonography
Light(830nm) vs.. UltrasoundSpeedResolution(10 micron vs100) Noncontact vs. contact
OCT vs SONO
Scan protocol
Line scan
Circle scan
Radial line scan
Reflectivity
Qualitative analysis of the OCT scan includes observation of the reflective qualities of the retinal structures. The OCT software assigns "cooler" colors (green, blue) to structures with lower reflectivity. It assigns "warmer" colors (yellow, orange, red) to more highly reflective structures. White represents the most highly reflective structures, and black represents the least reflective structures.
On the OCT scan of a normal retina, the NFL and RPE are
highly reflective, the middle retinal layers are medium reflective, and the photoreceptors (just above the RPE layer) are low reflective.
Normal retinal layers in OCT
Anterior segment OCT
Angle assessment ■ Pachymetry ■ Glaucoma surgery evaluation ■ Evaluation of corneal transplant ■ Visualization of the sclera/suprachoroidal
space ■ Identification of iris lesions ■ Evaluation of crystalline lens,
pseudophakic IOLs
Visante OCT
Top hat approach PKP
Donor tissue depth
Zigzag approach PKPxwXD5VcxwXD5VcxwXD5Vc
Endothelial keratoplastyxwXD5Vc
Normal AC angle
Narrow angle
Open PI in plateau iris
Peripheral Anterior SynechiaxwXD5Vc
Iris cystxwXD5Vc
irridoschisis
Anerior ChamberAngle tumorxwXD5Vc
Suprachoroidal effusionxwXD5Vc
IOL tiltxwXD5Vc
Shallow AC needs lensectomyxwXD5Vc