CSLO
CSLO uses low-power laser scans of the retina to produce a three-dimensional tomographic image of the ONH. This allows quantification of various structural parameters.
The first commercial device (Laser tomographic scanner; Heidelberg Engineering) was developed in the late 1980s. Hardware improvements resulted in the release of the Heidelberg Retinal Tomograph (HRT) in 1991. Further hardware and software improvements resulted in the more compact HRT II, released in 1999 [see Figure]. A notebook-based version (HRT III), with further software analysis refinements and an enlarged normative database was released in 2005.
Figure: Heidelberg Retinal Tomograph
(Heidelberg Engineering GmbH, Germany)
The HRT is a confocal laser scanning system.
- The fundus is scanned in a raster pattern (15° field of view, 384x384 pixels) with a 670-nm (red) laser.
- A laser beam scans the region of interest at the fundus at one focal plane to form an optical section. The focal plane depth is then adjusted, so that a series of optical sections at different depths is acquired.
- The HRTII and HRTIII acquire between 16 and 64 optical sections (automatically determined according to cup depth), with the focus of the first section in the vitreous in front of the optic nerve and the focus of the last behind the lamina cribrosa.
Figure: HRT Optical sections
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