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Editors Selection IGR 8-4

Structure and Function: RGC count estimates and progression to glaucoma

Comment by Ronald Harwerth on:

53714 Predicting progression in glaucoma suspects with longitudinal estimates of retinal ganglion cell counts, Meira-Freitas D; Lisboa R; Tatham A et al., Investigative Ophthalmology and Visual Science, 2013; 54: 4174-4183

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Over the past year-and-a-half, Medeiros and colleagues have published a series of studies of glaucomatous neuropathy that utilizes an innovative structure-function model to estimate the stage of disease. Their neuronal-based model utilizes a weighted average that estimates the RGCs underlying clinical measurements of structure (RNFL thickness) and function (visual fields). I will mention that the empirical models for estimating the neuronal substrates for perimetric sensitivity and RNFL thickness were derived from our studies, initially, on experimental glaucoma and then adapted to clinical patients. However, the innovation of the model developed by Medeiros' group is a weighting of the two RGC estimates to emphasize RNFL measurements for early glaucoma and SAP measurements for later stages of disease. The model for combining RGC estimates from SAP and OCT has been utilized for investigations of, for example, glaucomatous progression, the early detection of glaucoma, the relationship between RGC loss and VFI, the correlation of RGC loss and clinical ONH cupping ONH and, in the present publication, the characteristics of estimated RGC loss for glaucoma suspects who convert to clinical patients, compared to those who do not. The results of the investigation are intuitive in that the glaucoma suspects with less RGC's at baseline and those who have a steeper slope of RGC loss with time will be the converters. Thus, this study, along with the others from this group, provides interesting and important information that is relevant to understanding the pathology of glaucoma, but it has limitations in that it is a global estimate with high inter- and intra-subject variability. Therefore, for translation to clinical application, the methods can be improved through better mapping the visual fields onto the ONH, increasing the resolution of perimetric sensitivity measurements, eliminating some of the non-neuronal composition of the RNFL (e.g., blood vessels), and defining the remodeling, especially the Muller glia, during progressive RNFL thinning in glaucoma.

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