Optical Coherence Tomography is a diagnostic imaging technique that examines living tissue non-invasively. It is based on a complex analysis of the reflection of low coherence radiation from the tissue under examination.OCT allows both qualitative and quantitative analysis of the retina .Qualitative analysis includes description by location, a description of form and structure, identification of anomalous structures, and observation of the reflective qualities of the retina.OCT allows both qualitative and quantitative analysis of the retina.
Qualitative analysis includes description by location, a description of form and structure, identification of anomalous structures, and observation of the reflective qualities of the retina.Quantitative analysis involves measurements of the retina, specifically retinal thickness and volume, and nerve fiber layer thickness. This is possible because the OCT software is able to identify and "trace" two key layers of the retina, the NFL and RPE.
How does it work ?
- 128 to 768 axial samples (A-scans) in a single "scan pass"
- Each A-scan has 1024 data points and is 2 mm long (deep).
- When all of the A-scans are combined into one image, the image has a resolving power of about 10 microns vertically and 20 microns horizontally
- Compare that to the resolution of a good ophthalmic ultrasound at 100 microns
- The Zeiss OCT 3 has several built-in protocols for scanning the retina and the optic nerve head.
- A protocol is simply a pre-determined procedure or method
Scan Protocol Types
- Line - The "line" scan simply scans in a single, straight line. The length of the line can be changed as well as the scan angle.
- Circle - The "circle" scans in a circle instead of a line.
- Radial Lines - The "radial lines" scans 6 consecutive line scans in a star pattern
Not All OCT Scans Are Created Equally
- The "fast" scan protocols of the OCT 3 reduce the time needed for multiple scans
- The scan time reduction is intended to minimize the error created by patient movement
- Fast scans grab fewer A-scans in the 6 mm length of the scan. The normal 6 mm scan contains 512 A-scans, whereas the fast 6 mm scan contains only 128 A-scans, resulting in a lower resolution image