Effect of OCT B-scan Density on Sensitivity for Detection of Intraretinal Hyperreflective Foci

Abstract

Purpose : Intraretinal hyperreflective foci (IHRF) have been identified as an important optical coherence tomography (OCT) biomarker for progression of age-related macular degeneration (AMD). In this study, we evaluate the impact of reducing B-scan density on the sensitivity for detecting IHRF on spectral domain OCT (SD-OCT) volumes in eyes with intermediate AMD.

Methods : A total of 165 eyes from 106 patients with intermediate AMD and IHRF enrolled in the Amish Eye Study were evaluated in this retrospective analysis. For each case, raw SD-OCT (Cirrus OCT 512x128, 6x6mm, fovea centered) volumes were imported into 3D-OCTOR software. The number of IHRF was assessed on all 128 B-scans (spaced 47 μm apart) using a categorical scale (graded as 1-4, 5-9, 10-14, 15-19, and >20). Additionally, B-scan densities in the volume were lowered to 64 B-scans (spaced 94 μm apart), 43 B-scans (spaced 140 μm apart), and 32 B-scans (spaced 188 μm apart), respectively, by removing intervening B-scans prior to presenting the volume to the grader. The number of eyes with any IHRF and the number category of IHRF were used to compare the sensitivity at each reduced B-scan density against the reference 128 B-scan volume.

Results : In the reference 128 B-scan volume, there was a median IHRF score of 1-4 IHRF/eye. For the primary analysis of qualitative presence or absence of IHRF, the sensitivity decreased with decreasing B-scan density from 98.2% (p= 0.0819) at 64 B-scans, 92.7% (p<0.0001) at 43 B-scans, and 75.2% (p<0.0001) at 32 B-scans. With regards to the number of IHRF/eye, there was no significant difference in the numerical category when the density was reduced to 64 B-scans (P=0.0753) but was significantly different (with a lower level on the scale chosen) when the B-scan density was reduced to 43 or 32 B-scans (p<0.0001 and p<0.0001, respectively).

Conclusions : Increasing the inter B-scan spacing from 47 to 188 microns significantly reduced the ability to accurately determine whether IHRF were present in an eye. For quantification of the severity of IHRF within an eye, even an increase in inter B-scan spacing to 140 microns, was associated with a significant misclassification of the IHRF quantity. These findings may be of relevance in the design of OCT scanning protocols for studies utilizing biomarkers for AMD progression.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.

 

Figure 1 Effect of reduced B-scan density on measurement of hyperreflective foci (IHRF) in eyes with AMD