Purpose:
To compare rim area (RA) variability and RA change/time when three different reference planes (RP) are applied to longitudinal HRT data.
Methods:
The standard RP, 320 RP (320 µm below the peripheral reference ring) and an experimental RP (JC Tan – IOVS 2003) were compared. Global RA and 30° sector RA values were calculated from image series acquired from 31 ocular hypertensives (OHT) and 19 controls followed prospectively (1993–2001) with the HRT I. The OHT subjects converted to glaucoma (Advanced Glaucoma Intervention Study visual field criteria) during the study period. Linear regression of global and sector RA / time was performed. Variability was estimated from residual standard deviation (RSD) and coefficient of variation (CV), defined as RSD/mean*100. RA variability and slopes of RA/time were compared (paired t–test, p < 0.05). To estimate the facility to identify change, RSD/progression slope (RA/time) was calculated.
Results:
The 320 and experimental RP generated lower global RA variability than the standard RP, based on RSD. There was no difference between RPs for global RA in the normal group. Within 30° sectors of the converter group, the experimental RP was found to have lower RSD in all sectors compared to the standard RP, and in the temporal sectors compared to the 320 RP. CV was least in most sectors using the experimental RP, both within the normal and converter group. There was no significant difference between RPs for the global RA/time slope coefficients. Considering RSD/slope in the converter group, the least variable RP is the experimental, particularly in the temporal sector where RA measurements are least reliable (Figure).
Conclusions:
The experimental reference plane appears to offer improved RA variability, particularly in the temporal sector, compared to the more established reference planes. A newer 320 RP, with a more stable location, has yet to be tested.
Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • imaging/image analysis: clinical • optic disc