Imaging the optic nerve and ganglion cell layer.

New imaging techniques have extended the limitations of visualisation of the structures of the optic nerve and fundus in the living human eye. Quantitative reconstruction of depth of the optic nerve head is becoming widely available through the use of the confocal scanning laser ophthalmoscope (cSLO). A separate method of quantitative depth reconstruction is possible using stereo pairs which is not subject to the same artefacts as the tomographic reconstruction. We are investigating the use of these techniques both with conventional stereo imaging and using stereo pairs derived from cSLO images. In these we find that there is additional structural detail evident in the base of the optic nerve head. Further studies made with an instrument optimised to image this region show that this corresponds to the lamina cribrosa. Current work is aimed at further extending the limits of imaging using techniques based on optical coherence tomography, which provides additional depth resolution. Results to date with a prototype device show an improvement of approximately a factor of 10 in depth resolution and that some separate layers of the retina may be visualised including the photoreceptor layer. The goal is to extend these limits to allow visualisation of the ganglion cell layer.