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Editors Selection IGR 20-2

Structural Examination Methods: Age dependent ONH changes by HRT

Comment by Linda Zangwill on:

27117 Change in optic nerve head topography in healthy volunteers: An 11-year follow-up, Harju M; Kurvinen L; Saari J et al., British Journal of Ophthalmology, 2010;

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Estimating age-related changes in optic nerve head topography is important so that clinicians can better differentiate between age-related and glaucomatous change. There have been very few studies that have followed healthy volunteers with structural measurements over a long period of time; most of the estimates of age-related structural change have been calculated from cross-sectional data. In this relatively small cohort study by Harju et al. (1697), 36 healthy volunteers between the ages of 24 and 68 years (median age 37 years) had one baseline Heidelberg Retina Tomograph (HRT) I scan and one HRT I scan obtained seven to thirteen years later. Comparing these two HRT scans, the authors found increased cupping and neuroretinal rim thinning and conclude that topographic age-dependent changes occur and are detectable with the HRT.

Optical imaging instruments improve our ability to identify small structural changes

The authors correctly suggest that it is inappropriate to make age-specific or quantitative conclusions about age related change in this study since it is unclear whether change in is linear and there are other possible explanations for the topographic changes found in this study including changes in the reference plane height, and changes in the quality of the scan ‐ perhaps due in part to the development of media opacities. It should be noted that this study confirmed several previous crosssectional previous reports that a decrease in HRT reference plane based retinal nerve fiber thickness (RNFL) measurements with age were not found. RNFL decrease with age has been reported using OCT and GDx that measure the RNFL directly. Moreover, the authors report that 29% of eyes had a worsening in a Global or Regional Moorfields Regression Analysis result. In contrast, only one eye had a worsening of the Glaucoma Probability Score result.

Optical imaging instruments improve our ability to identify small structural changes, but not all statistically significant change is clinically significant or is related to the disease process.

Not all statistically significant change is clinically significant or is related to the disease process

As clinicians apply results from imaging instruments to identify glaucomatous change, it is important not only to recognize significant change, but to estimate the rate of that change in order to identify patients whose rate of change will likely lead to visual function loss in their lifetime. Depending on the age and life expectancy of the patient, patients with slowly progressing disease may require less aggressive treatment or no treatment at all when significant visual function loss in not expected in their lifetime. Better estimates of the rates of change in healthy eyes with multiple measurements over a long period of time are still needed to help differentiate between age-related and glaucomatous change.

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