Abstract
Purpose :
A simple model of the change in circumpapillary retinal nerve fiber layer (cRNFL) thickness with increased diameter of optical coherent tomography (OCT) circle scans of the disc was tested with data from glaucoma patients and healthy controls.
Methods :
Spectral-domain OCT circle scans of the disc (Spectralis, Heidelberg Eng) with diameters 3.5mm (d0) and 4.7mm (d1) were obtained from 50 eyes: 25 healthy controls (H) and 25 with early glaucoma (G).[1] The model predicted the average cRNFL thickness at d1 based on the measurement at d0 for global, nasal superior (NS), nasal (N), nasal inferior (NI), temporal inferior (TI), temporal (T), and temporal superior (TS) disc sectors based on the assumption that total cRNFL volume is constant: T1pred = (d0/d1)*T0, where T0 is the average thickness at d0. R^2 values and graphical analysis of residuals were used to assess the model.
Results :
For H eyes, R^2 ranged from 0.872 for global to 0.100 for TI, while for G eyes, R^2 ranged from 0.880 for global to 0.558 for TS (Table). For both H and G eyes, the model fits the global measure well, suggesting that the overall cpRNFL volume was approximately constant with increased diameter, although there was a tendency for the model to under predict the G data (red arrow in Fig. 1B). On the other hand, for both H and G eyes, the model under predicted the NI thickness and over-predicted TI thickness, as can be seen in Fig 1C-F. The same trend was true for NS and TS (not shown), suggesting a systematic deviation from the model.
Conclusions :
The fit of the model suggests that the total (global) cRNFL volume is roughly constant between the 3.5mm and 4.7mm diameter circles in H eye. The slight underprediction of global thickness for G eyes is consistent with the view that the cRNFL consists of RNF and a “residual”, which is made up of blood vessels and glial cells. [2] The under prediction in NI and over prediction in TI, for both H and G, is likely attributable to the fact that the arcuate bundles, and associated blood vessels, deviate toward the temporal region and away from the radial course assumed by the model. These results have implication for those seeking to combine information from circle scans of different diameters. 1. Hood, Tsamis et al, IOVS 2019 [2] Hood, Raza et al, PRER 2013.
This is a 2020 ARVO Annual Meeting abstract.