Calcified drusen prevent optical coherence tomography angiography from assessing the underlying choriocapillaris.

Abstract

Purpose : In age-related macular degeneration (AMD), the choriocapillaris (CC) flow deficits (CCFDs) under typical drusen can be measured using established compensation strategies. This study investigates whether CCFDs can be quantified under calcified drusen.

Methods : CCFDs were measured in 30 AMD eyes with calcified drusen, 30 AMD eyes with soft drusen, and 30 normal eyes. Drusen and calcified drusen were identified and classified based on their appearance using OCT images, and then manually outlined to generate corresponding masks. CCFDs were obtained using a validated algorithm with an established compensation strategy, from which the CCFD density masks were generated to indicate the regions with increased CCFDs. Dice similarity coefficients were calculated between the CCFD masks and both typical drusen masks and calcified drusen masks (Fig. 1). A phantom experiment was conducted to simulate the impact of light scattering that arises from calcified drusen.

Results : The area measurements of CCFDs were highly correlated with the area measurements of calcified drusen but not typical drusen, suggesting an association between calcified drusen and underlying CCFDs. But unlike typical drusen, calcified drusen gave rise to an illusional OCT structural signal in the defined CC layer that does not associate with choriocapillaris flow signal. Phantom experiments showed that the presence of highly scattering material similar to the content of calcified drusen caused a scattering tail that generated a false signal located at the CC structural layer, which prevents the detection of OCTA choriocapillaris signals (Fig 2). The phantom experiment confirmed that the calcified drusen stop the light from penetrating deeper into the choroid resulting in en face hypotransmission (hypoTD) defects.

Conclusions : The high scattering property of calcified drusen causes a scattering tail under these drusen that does not carry OCTA signal from choriocapillaris, preventing OCTA from assessing the CCFDs. For this reason, CCFDs cannot be reliably measured under calcified drusen and calcified drusen need to be identified and excluded from macular CCFD measurements in the assessment of AMD progression.

This abstract was presented at the 2024 ARVO Imaging in the Eye Conference, held in Seattle, WA, May 4, 2024.