OCT/SLO System
Introduction and Theory of Operation
The OCT/SLO is an Optical imaging system designed to image the vitreo-retinal
structure, the retinal layers as well as provide a confocal fundus image. It is based on a
dual channel system, built around an interferometer and a confocal receiver. The OCT
channel resolves retinal structures by measuring the time delay of light that is back-
scattered from different micro-structural layers in the retina. It produces cross-sectional
images (B-Scan) or coronal (C-Scan) images of the retina. The confocal receiver operates
similar to a scanning laser ophthalmoscope (SLO) and produces fundus images of the
retina and the optic nerve.
The OCT/SLO operates in two scanning modes:
•B-Scan OCT - producing cross sectional images
and
•C-Scan OCT – producing coronal images
In both modes of operation, two images are simultaneously produced and displayed, one
OCT and the other Confocal image of the fundus. The OCT/SLO uses light generated
from an infrared broadband Super Luminescent Diode (SLD) source with a wavelength
between 790 nm to 950 nm. The interferometer combines the reflected light from the
retina with the reflected light from a reference mirror. A photo-detector unit detects and
measure the interference and sends the signal to a computer that generates the OCT
image. Part of the light backscattered from the retina is also diverted to a photo-receiver
via a small pinhole, the photo detector detected the signal which is then amplified and
sent to the same computer which generates a Confocal Ophthalmoscope image of the
fundus simultaneously with the OCT image. As both the confocal fundus (retinal surface)
image and the OCT images are generated through the same optics at the same time, they
are displayed simultaneously on the computer screen and are pixel to pixel
correspondent.
In the B-Scan Mode the OCT/SLO projects light onto to the retina through Galvano-
Scanning mirror system which moves the beam in a horizontal line (vertical line or
diagonal or circular line). The OCT image is analogous to ultrasound B-Scan and
represents a longitudinal cross sectional image of the retina, its sub-layers and internal
structures.
In the C-Scan (Coronal) Mode the OCT/SLO projects the light into the retina through a
pair of X,Y Galvano-Scanners which move the beam in a raster fashion across the surface
of the retina. . The C-Scan Coronal OCT images are plane generated at different (preset
and pre-selected) Z depths. Each C-Scan OCT represents a X,Y Plane at a given Z depth.
