Abstract
Purpose :
To study how optic disc area influences Retinal Nerve Fiber Layer (RNFL) topography and circumpapillary RNFL thickness measurements with OCT.
Methods :
180 healthy subjects with varying optic disc areas (DA) were included. The relationship between DA and circumpapillary RNFL thickness was tested with Pearson correlation coefficient (r). Eyes were grouped into tertiles by DA: tertile 1 (small DA, n=60), tertile 2 (normal DA, n=60), tertile 3 (large DA, n=60). RNFL thickness between tertiles was analyzed with ANOVA. Using ImageJ software, CIRRUS OCT RNFL scans were analyzed (n=97). The RNFL bundle was defined as values above the modal RNFL thickness, and RNFL bundle volume (BV) was found by multiplying RNFL bundle area with average RNFL bundle thickness. Pearson r was calculated between DA and BV. RNFL thickness topography was elucidated via the average of 252 radial spoke line graphs originating from the optic disc center to the periphery of the RNFL scan. From the line graph, peak retinal thickness (PRT), distance from PRT to the circumpapillary measurement of 3.46mm (PRT-to-3.46mm), distance from disc margin to PRT (DTP), and slope at 3.46mm (SLP) were extracted.
Results :
The average RNFL thickness was 93.3 ± 10.5μm. DA was significantly correlated with RNFL thickness (r= 0.505, P<0.001). The differences in RNFL thickness means across tertiles were statistically significant with RNFL thickness averages of 87.1 μm, 91.3 μm, and 101.2 μm across Tertiles 1, 2, and 3, respectively (p<0.001). DA was not correlated with BV (r= 0.080). Topography analysis showed a strong correlation between DA and PRT-to-3.46mm (r= -0.777, P<0.001) however DA and PRT are negatively correlated (r= -0.388, P< 0.001), reducing the strength of association between DA and circumpapillary RNFL thickness. DTP and SLP were weakly corelated with DA (r= 0.353, P<0.001 and r=-0.060, P<0.008, respectively).
Conclusions :
DA should be considered in the interpretation of circumpapillary RNFL thickness. Healthy eyes with small discs produce falsely low circumpapillary RNFL thickness values, and vice versa.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.