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Editors Selection IGR 23-2
Clinical Examination Methods: RNFL and macular thickness I
Comment by Harsha Rao on:
54661 Impact of Age-related Change of Retinal Nerve Fiber Layer and Macular Thicknesses on Evaluation of Glaucoma Progression, Leung CK; Ye C; Weinreb RN et al., Ophthalmology, 2013; 120: 2485-2492
Detecting structural progression in glaucoma is a challenging task because of the multiple confounders that affect the structural measurements over time. In addition, a clear consensus on the magnitude of structural change that is clinically significant is also lacking. Therefore, most of the earlier studies have considered 'any' statistically significant structural change (slope) as 'progression'. Leung et al. In a recent study attempt to address both the above issues by evaluating the effect of one of the predominant confounders in detecting glaucoma progression on SDOCT: the normal age-related structural change. They found that the percentage of eyes showing statistically significant progression on macular parameters significantly reduced after adjusting for the normal age-related loss (50% vs 14.7% by ganglion cell-inner plexiform layer thickness before and after adjusting for age-related change).
age-related change was relevant to the assessment of glaucoma progression, particularly when the macular measurements were examined
The percentage of eyes progressing on peripapillary RNFL thickness before and after adjusting for age-related change however was similar (27.3% and 26%, respectively). They concluded that accounting for age-related change was relevant to the assessment of glaucoma progression, particularly when the macular measurements were examined. Although this is a very important study in the context of evaluating glaucoma progression on imaging techniques, there are a few things to note. Firstly, the authors used linear mixed modeling approach for the age-related change in normal subjects and the ordinary least square regression for the rate of change in glaucoma eyes. Previous studies have shown that the estimates can be different between these two modeling methods. Secondly and on a larger clinical perspective, this study stops at comparing the percentage of eyes that are labeled as progressing on SDOCT before and after adjusting for age-related change, but doesn't validate the results. Validating the eyes progressing before and after adjustment with the eyes progressing on visual fields or on disc photographs or on clinical assessments would have actually shown the utility of adjusting for the age-related change during evaluation of structural progression.
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