The development of the scanning laser ophthalmoscope (SLO), first conceived by Webb et al in 19801 heralded the first widespread application of lasers for retinal imaging. A highly collimated beam from a laser is swept over the retina delivering all its energy to a very small spot for a very short time, typically of the order of some tens of nanoseconds. Light reflected from the spot is detected and synchronously decoded to form an image on a monitor.

The use of a laser in this way offers a number of fundamental advantages for retinal imaging:

• as the input laser beam occupies only a small part of the pupil most of the pupil is available for light collection permitting non-mydriatic imaging and levels of illumination that are a factor of 200 lower than with the fundus camera

• there is no need to employ high intensity flash so rapid imaging can be carried out offering the potential for serial imaging

• since imaging is carried out point by point, data are readily acquired as digital images allowing quantitative measurements and image processing

• since the detected light is focused at a single point confocal imaging can be employed to give three dimensional images

• the scattered light can be imaged separately from the reflected component, Tyndall imaging, to enhance pathological structures that have a high scattering component

• the wavelength of the illuminating light can be selected by choice of laser so offering the potential for multispectral imaging

• changes in polarisation of the reflected light can be used to measure retinal nerve fibre layer (RNFL) thickness.

While a number of these factors make imaging simpler there are three major advances that the SLO offers to retinal imaging—the ability to do quantitative imaging, multispectral imaging, and three dimensional imaging.