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