Nerve fibre layer thickness measurements derived by scanning laser polarimetry: the jury is out

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Abstract
The morphological impact of glaucomatous optic neuropathy includes a loss of retinal ganglion cells which is clinically manifested as optic nerve head damage and localised, or diffuse, dropout of the retinal nerve fibre layer (RNFL).1There is considerable variability in, and overlap of, the current clinical variables used to differentiate normal from glaucomatous populations. Optic nerve head damage can also be clinically observed before manifest visual field loss.2 3 Indeed, histological evidence gained from the retinal ganglion cell counts of three human postmortem eyes which had also recently undergone automated perimetry has suggested that substantial ganglion cell loss can occur before a manifest and repeatable reduction of static perimetric sensitivity.4 Consequently, the development of non-invasive, objective techniques which measure those retinal structures most likely to suffer glaucomatous damage has been proposed to aid the diagnosis of glaucoma and improve the monitoring of progressive glaucomatous damage. Scanning laser polarimetry is an example of such a technique.5 Scanning laser polarimetry purports to measure, in vivo, the thickness of the RNFL. The technique utilises a confocal scanning laser ophthalmoscope in conjunction with an integrated polarimeter to project a polarised spot of laser light …