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Hin Cheung, William H Swanson; Assessing variability in attenuation coefficient of the retinal nerve fiber layer using optical coherence tomography. Invest. Ophthalmol. Vis. Sci. 2020;61(7):2527.
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© ARVO (1962-2015); The Authors (2016-present)
We have demonstrated success in using retinal nerve fiber layer (RNFL) attenuation coefficient (AC) generated from spectral domain optical coherence tomography scans to identify RNFL abnormalities in patients with glaucoma (Cheung H, et al. IOVS 2019;60:ARVO E-Abstract 5608). However, better understanding of normal between-subject variability is needed before it can be translated to clinical use. This exploratory study assesses between-subject variability in healthy eyes as a first step to establishing a normative reference range.
One eye of sixty controls was imaged, 30 older (68 years ± 9) and 30 younger (27 years ± 3), each group with 17 males and 13 females, and axial length measurements were collected. Log AC values were generated with the same protocol developed previously. To avoid superficial glial proliferations and specular reflections and to ensure the depth remains within the RNFL, log AC was assessed at 4µm steps between 24µm to 48µm below the internal limiting membrane (ILM).
Log AC was 0.1 log unit higher in younger controls compared to older controls at all 7 depths below the ILM. At 40µm, the mean (± standard deviation) was 0.27 ± 0.13 for the younger group and 0.16 ± 0.11 for the older group (t > 3, p < 0.001); this was similar for the other 6 depths. At 40µm, linear regression of log AC versus age in the older group showed a slope of -0.03 log unit per decade (r = -0.24, p = 0.10); and similarly for the other 6 depths. Within-subject variability was generally low in both groups (median standard deviation 0.10), but a few individuals in each group had standard deviations greater than 0.15. The correlation of log AC with axial length was (r = -0.37, p = 0.02) for the younger group and (r = -0.05, p = 0.40) in the older group.
There is a difference in log AC between the younger and older group, but the effect of age in the older group was small. There was a mild correlation between axial length and log AC in the younger group but not in the older group. Between-subject variability was relatively small in both age groups, further reduction by accounting for age and axial length would be modest. Future direction to reduce within-subject variability may be more fruitful.
This is a 2020 ARVO Annual Meeting abstract.
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