Enhanced Depth Imaging Optical Coherence Tomography Technology Reveals a Significant Association Between Optic Nerve Drusen Anterior Displacement and Retinal Nerve Fiber Layer Thinning Over Time

BACKGROUND Optic disc drusen (ODD) are a dynamic phenomenon, and their appearance, size, and relative location may change. The purpose of this study is to evaluate and quantify the longitudinal changes of buried ODD with enhanced depth imaging (EDI) optical coherence tomography (OCT) over time. METHODS ODD were analyzed with Spectralis OCT (Heidelberg Engineering, Heidelberg, Germany) and EDI technology. The peripapillary retinal nerve fiber layer (RNFL) thickness was also measured. The size and depth of ODD were compared between the baseline and study visit (at least 2 years of follow-up), and the changes were correlated with mean RNFL thickness. The repeatability, coefficient of variation, and cutoff values for size and depth on EDI-OCT were calculated. RESULTS Of 21 previously identified patients with ODD, only 12 patients (21 eyes) met the most recent diagnostic criteria according to the ODD Studies Consortium recommendations for using OCT-EDI technology. The 21 eyes were reanalyzed after a mean period of 44.7 ± 13.2 months (range: 24-71 months). Overall, 132 ODD were evaluated with a mean of 6.1 ± 2.5 ODD per eye and 1.9 ± 1.1 ODD per scan. Overall, we found a significant forward movement of the drusen between visits (P = 0.01). Most drusen (67.4%) moved anteriorly, and in approximately one-third (35.6%), this displacement exceeded the cutoff value (64.28 µm). Furthermore, we found a significant correlation between ODD shallowing and RNFL thinning during the follow-up (P ≤ 0.03; R ≥ 0.370). We did not find any significant changes in size measurements (P = 0.10) over time. CONCLUSIONS In approximately one-third of buried ODD, a significant anterior movement occurred over 2 years of follow-up, and this movement was associated with significant RNFL thinning. By contrast, no significant change was detected in the size of the buried ODD.