Quantitative measure of optic disc drusen location in enhanced depth imaging optical coherence tomography scans

Purpose : A quantitative measure of anatomical optic disc drusen (ODD) location in the optic nerve head can be an important parameter in the investigation of ODD formation and the development of visual field defects. We propose a method for defining a quantitative measure of ODD location relative to Bruch’s membrane.

Methods : Optic disc drusen in high resolution enhanced depth imaging optical coherence tomography scans were manually segmented using ITK-SNAP by a trained ophthalmologist. To quantify a location of each ODD, we need a reference. Bruch’s membrane serves as an excellent reference, but does not exist within the optic nerve head, where the ODD are located.

Therefore we performed a semi-automatic graph based segmentation of Bruch’s membrane at the margin in each B-scans. From the segmentation we obtained two landmarks per B-scan. Based on the landmarks in each B-scan, we defined a reference surface relative to Bruch’s membrane. The Euclidean distance from the center of mass of each manually segmented ODD to the defined reference surface gave a quantitative measurement of each druse location.

Furthermore, the quantitative measure was signed which indicated whether the ODD was located above or below the reference surface. Results : We computed a reference surface (Fig. 1) based on Bruch’s membrane segmented at the margin in 97 B-scans per patient for 37 patients in total (Fig. 2). The average number of ODD was 4.4 (± 5.78) per patient and the average distance from the center of mass for each ODD to the defined reference surface was 0.19 mm (± 0.3 mm).

Conclusions : A defined reference surface based on Bruch’s membrane in ODD patients resulted in a quantitative measure of ODD location. The quantitative measure indicates whether the ODD is located above or below the reference surface. The quantitative measure of anatomical ODD location can act as an important parameter in future ODD research.