Optic nerve head rim tissue thins more rapidly than peripapillary retinal nerve fiber layer tissue in early glaucoma.

Abstract

Purpose : We have shown that optic nerve head (ONH) minimum rim area (MRA) decreases more than peripapillary retinal nerve fiber layer area (RNFLA) in monkeys with early experimental glaucoma (IOVS 2016;57:4403-11). Here we sought to determine if this observation would translate to human glaucoma by evaluating participants of the Portland Progression Project, who had high-risk ocular hypertension or non-endstage glaucoma at the start of the study.

Methods : OCT and standard automated perimetry (SAP) were obtained every ~6 mos. Data were analyzed for a series of 7 visits (3.3 ± 0.4 yrs) from one eye each of 157 participants. SAP mean deviation (MD) ranged from -16.9 to +2.2 dB (average: -0.8 dB). OCT MRA was derived from 24 radial B-scans centered on the ONH by summing the areas of each of the 48 trapezoids whose base is centered on a Bruch’s membrane opening point and whose height is the distance to the retinal/ONH surface segmentation that minimizes its area (AJO 2014;157:540-9). RNFL thickness measured from a peripapillary 12° diameter circular B-scan was multiplied by scan circumference to obtain RNFLA.

Results : At the first visit, MRA (1.06 ± 0.26 mm²) was slightly larger than RNFLA (1.00 ± 0.18 mm²; Wilcoxon P<0.0001). Over 7 visits, MRA decreased at a rate of -0.018 ± 0.017 mm²/yr (P<0.0001), which was faster (P<0.0001) than RNFLA (-0.011 ± 0.013 mm²/yr; P<0.0001). Both the raw difference (MRA-RNFLA) and the ratio (MRA:RNFLA) decreased over time (P<0.0001 each), consistent with the steeper slopes observed for MRA. SAP MD also declined over the same time (-0.078 ± 0.40 dB/yr, P=0.02). MRA and RNFLA at the first visit were each predictive of MD slope (R=0.20, P=0.01 and R=0.24, P=0.002, respectively). The MRA-RNFLA difference was not linearly related to damage severity: for eyes with more damage (to the left in Fig1), the MRA-RNFLA difference was not related to severity; but for eyes with less damage (to the right in Fig1), the MRA-RNFLA difference was related to severity. Similarly, MRA declined fastest and the difference between MRA and RNFLA slopes was greatest for eyes in the earliest stage of structural or functional damage (Fig2).

Conclusions : ONH rim tissue thins faster than the peripapillary RNFL in the earliest stages of glaucoma, but at a similar rate in later stages. The difference between MRA and RNFLA changes may represent a structural signature of early glaucoma.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.