Retinal nerve fibre layer mapping
Possible to detect glaucomatous changes much earlier than with conventional optic disc stereo photography
With retinal nerve fibre layer (RNFL) mapping it is possible to detect glaucomatous changes much earlier than is the case with conventional optic disc stereo photography, according to Jeffrey Liebmann MD, Colombia Medical University, New York,
“By concentrating on the RNFL, detecting change over time we are much better able to detect early damage and perhaps adjust our treatment,” Dr Liebmann said.
He noted that glaucoma is a progressive optic neurodegeneration, with laminar degeneration being the hallmark of the disease process along with the associated retinal ganglion cells damage. Posterior to the lamina, the optic nerve is damaged as well with atrophy moving to the lateral geniculate body and the visual cortex.
The traditional way of assessing and monitoring glaucomatous neurodegeneration is to look for change in the neuroretinal rim with optic disc photography. Additional features of the disease detectable by this means include expansion of peripapillary atrophy and disc haemorrhage. Occasionally ophthalmoscopy can provide an indication of whether the disease is present or progressive.
EXTENDING THE SENSES
However, the use of modern imaging devices extends the diagnostician’s senses and reveals more about the disease process than can be achieved with disc photography, Dr Liebmann said. He cited a recently published study which showed that eyes that developed nerve fibre layer damage detected by OCT had an eightfold higher chance of developing a visual field deficit than those which did not. Furthermore, eyes with RNFL thinning progressed at a much more rapid rate and had much more visual field progression. (Yu et al, Ophthalmology 2016;1231:201-210)
He added that previous research has shown that over time there is a very precise structure-structure correlation between development of nerve fibre layer defects in the optic nerve and corresponding damage in the macular region. (Hood et al, PRER 2013; 32:1-25 )
Moreover, the technology can provide additional insight into the structure/function relationship in the natural history of the disease. For example, with optical coherence tomography measurements it has been shown that many of the early changes in glaucoma occur in the macula and that this corresponds with circumpapillary RNFL thinning. Local macular damage is more common and more severe when it occurs close to fixation in the inferior retina/ superior visual field.
“It’s important to track the rate at which patients are changing. In very slowly progressing disease we may not need to advance treatment for those patients, but those patients with significant RNFL loss over time are at risk and need to be treated more aggressively,” he said.