## 4 Discussions  
In this study, we developed a semi-automatic imaging analysis to quantify the 3D structure of the ppRPE/BM layer and used it to study morphological changes in patients following LP. We measured the angle of the ppRPE/BM layer in the OCT scans across all 12 radial directions. We found that the ppRPE/BM layer angle varied along different scanning directions, both before and after LP, while the LP-induced change in the ppRPE/BM layer angle was minimal along different scanning directions. We validated our method using 2 independent graders to review and manually segment each OCT scan when necessary. The averaged ppRPE/BM layer angle at each B-scan was proposed to eliminate tilting artifacts, which are inherent to OCT imaging acquisition. We propose that the mean ppRPE/BM layer angle change could serve as a biomarker to study the morphological changes of the ppRPE/BM layer in different clinical scenarios. Our unique segmentation method along with a regression model enabled us to quantify the morphology of the ppRPE/BM layer in 3D efficiently. The ppRPE/BM layer was segmented using OCTSEG software, with manual corrections if necessary [17]. The coordinate information of the segmented ppRPE/BM layer was used to calculate the ppRPE/BM layer angle using the linear regression model. The distance from the ppRPE/BM layer to its linear regression line was used to quantify the straightness of the ppRPE/BM layer. A threshold of 10 pixels (32 \(\upmu\)m) was used as the upper limit of \"straightness\". A good agreement was observed between the two graders (Figure 6) with ICCs close to one, indicating that the proposed method in quantifying the ppRPE/BM layer angle is robust. Only two eyes were excluded based on this criterion (supplementary material Figure S2). The ppRPE/BM layer angle \(\gamma\) at each radial scan segment was calculated using the slope of the linear regression line. The averaged ppRPE/BM layer angle \(\Gamma\) at each scan was proposed to eliminate the potential imaging artifacts. The magnitude of \(\Gamma\) varied significantly across different radial directions both before and after the LP (Figure 7). This is consistent with the observation by [PERSON] et al., who found that the ppRPE/BM shape before LP was different along different radial directions [15]. However, the ppRPE/BM layer angle changes following the LP did not vary significantly along different radial directions. This implied that exclusion of occasional radial OCT scans (e.g., scans with undistinguishable ppRPE/BM layers) would not significantly affect the mean of the ppRPE/BM layer angle change in that eye. Furthermore, the mean of the ppRPE/BM layer angle changes across all radial directions could serve as a biomarker to represent the 3D changes to the ppRPE/BM layer. This biomarker could integrate the ppRPE/BM layer angle change in 3D with less bias as compared to prior 2D quantifications in one designated scan direction. The paired t-test revealed the \(\Gamma\) after LP was significantly different from that before LP in all eyes except for one eye. The results also demonstrated the capacity of our method in detecting the changes of the ppRPE/BM layer angle following LP (Figure 9). Previous studies have shown the ppRPE/BM layer became more V-shaped in patients with intracranial hypertension and papilledema within 1 week following LP [10]. In this study, the mean of the ppRPE/BM layer angle changes across the 12 radial directions was calculated for each eye (Figure 9). The positive mean angle indicated a more V-shaped ppRPE/BM layer, which was only observed in 7 (44%) right eyes and 6 (43%) left eyes within 30 min following LP. There are several reasons why a positive mean angle change was not seen in all our subjects. First, this positive angle change may be related to the chronicity of ICP increase and papilledema. [PERSON] et al. reported that the deflections of the ppRPE/BM away from the vitreous were only seen in participants with high ICP and papilledema following the LP [9].