We read with interest the article by Horsley and associates reporting the effect of chronic anti–vascular endothelial growth factor therapy on retinal nerve fiber layer (RNFL) measurement in patients with wet age-related macular degeneration. The authors reported that long-term treatment with anti–vascular endothelial growth factor agents did not lead to significant changes in RNFL thickness measured with Stratus OCT (Carl Zeiss Meditec, Dublin, California, USA). However, the results may be confounded by image quality of RNFL measurement.
Image quality has been demonstrated to affect the accuracy and reliability of RNFL measurement in Stratus OCT. Thus, image quality always should be assessed when interpreting Stratus OCT reports in clinical practice. Previous studies have investigated the effect of signal strength and scan circle displacement on RNFL thickness measurement in Stratus OCT. It is reported that mean average RNFL measurement errors was 12.1 ± 11.4 μm on 0.7-mm scan circle displacement. In another study, Cheung and associates reported that signal strength was associated positively with RNFL measurements.
In the study by Horsley and associates, RNFL imaging was performed in a patient population with wet age-related macular degeneration. It may be a bit difficult to obtain good-quality images in these patients, who always have poor visual acuity at presentation. Therefore, the authors should have described whether all the included baseline and follow-up images were centered on the optic disc without scan circle displacement. Besides, a comparison of signal strength between the initial and last follow-up visit was recommended. Signal strength was probably better at the follow-up visit because of the potential improvement of visual acuity after anti–vascular endothelial growth factor therapy. Because better signal strength is associated with thicker RNFL measurement in Stratus OCT, this may confound the results of the study.