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Editors Selection IGR 7-3

Progression: Clinical estimation of ganglion cell loss

Comment by David Greenfield on:

51039 Estimating the rate of retinal ganglion cell loss in glaucoma, Medeiros FA; Zangwill LM; Anderson DR et al., American Journal of Ophthalmology, 2012; 154: 814-824.e1

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Measures of structure and function often disagree in glaucomatous eyes, particularly in patients with mild and advanced disease severity. Both are essential in order to monitor disease progression over time, but it is widely recognized some patients may develop isolated changes in a single measurement that correlates poorly with other measurements. In the present study, Medeiros and colleagues evaluated rates of neuronal loss based on an index of estimates of RGC counts combining structure and function. They were able to detect a larger number of glaucomatous eyes as progressing compared with the use of isolated measures of standard automated perimetry or time-domain OCT, while maintaining comparable specificity in a group of stable eyes. This is a very well-designed and -conducted study. The development of the combined structure and function estimate of RGC counts was based on previous work by Harwerth and associates utilizing nonhuman primates. A combined measure is quite logical since it would be expected to be equally sensitive for detecting progression in eyes at all stages of disease across the glaucoma continuum. The authors were careful to prospectively measure the rate of RNFL atrophy among a group of healthy subjects to estimate age-related RGC loss so that glaucomatous progression would be considered to occur if the rate of RGC loss was greater than the expected age-related loss. Additionally, specificity measures were also calculated using a group of stable glaucoma patients who underwent repeated visual field and OCT testing during a two-month time interval.

Rates of neuronal loss based on an index of estimates of RGC counts combining structure and function

OCT technology is rapidly advancing. The present study employed retinal nerve fiber layer thickness measurements obtained using Stratus OCT as the primary structural outcome measure. Future refinements in this model will likely incorporate direct measurements of retinal ganglion cell thickness in the macular region using high speed, high resolution OCT technology such as swept source OCT. As more robust change detection models emerge and undergo validation, clinicians and regulatory agencies will embrace these strategies. The authors are to be congratulated for moving us closer towards the estimation of in-vivo ganglion cell loss.

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