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RNFL thickness preferred for monitoring change in glaucoma
Researchers may prefer retinal nerve fiber layer thickness for monitoring change in glaucoma over minimum rim width and minimum rim area, which may be more accurate for early detection of glaucomatous damage, according to Gardiner and colleagues in Investigative Ophthalmology & Vision Science.
Data was compiled from 157 eyes in 157 participants with high-risk ocular hypertension or non-end-stage glaucoma; eyes were tested approximately every 6 months for at least six visits, according to the study. Researchers regressed minimum rim width (MRW), minimum rim area (MRA) and retinal nerve fiber layer thickness (RNFL) thickness linearly against time.
The median longitudinal signal-to-noise ratio (LSNR) was -0.58y-1 for RNFL thickness. Median LSNR for MRW was -.044y-1, and MRA was -0.23-1.
The researchers found that LSNRs were significantly more negative for RNFL thickness than for MRW.
A better (more negative) LSNR resulted for RNFL thickness than for MRW or MRA, according to the study.
“This indicates that when using spectral domain optical coherence tomography to assess glaucomatous structural change, RNFL thickness may be more useful, since true change related to axon loss should be easier to distinguish from noise,” the researchers wrote.
In conclusion, the lower LSNR achieved with RNFL thickness potentially suggests that it may be advantageous over other methods for assessing change. – by Abigail Sutton
Disclosure: The study was supported by National Institutes of Health grants as well as the Legacy Good Samaritan Foundation, Heidelberg Engineering, Alcon Research Institute and Sears Medical Trust. Gardiner reported he is a consultant for Carl Zeiss Meditec. Burgoyne has received support from Heidelberg Engineering and Reichert. All other authors reported no financial disclosures.
Perspective
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In a perfect world, clinicians would use in vivo retinal ganglion cell counts to assess glaucomatous damage. In the real world, we still rely on a number of proxies such as disc and nerve fiber layer assessment and visual fields.
Optical coherence tomography has rapidly become an invaluable objective adjunct to subjective examination.
Gardiner and colleagues have demonstrated that the greater signal-to-noise ratio and lower variability of retinal nerve fiber layer (RNFL) thickness measurement make it, at present, more sensitive than OCT-based neuroretinal rim analysis in detecting progression. Hence, they have added to our understanding of how to best leverage OCT-based assessment of structure and function throughout the glaucoma continuum in the following ways:
In establishing a diagnosis, structural change typically precedes functional loss, with optic disc change possibly preceding extrapapillary change.
In monitoring progression, RNFL thickness analysis may be of more value in early to moderate disease, while ganglion cell-inner plexiform layer thickness and visual field assessment become more helpful in advanced glaucoma.
Of course, the prudent clinician uses all available tools at all times. To this end, the authors conclude with these wise words: “Clinically, measuring multiple parameters within the optic nerve head, RNFL and macula may maximize early detection of damage without compromising the ability to use the same or a different combination of measurements to determine whether changes are occurring.”