Philip J. Rosenfeld

The impact of swept-source optical coherence tomography angiography (SS-OCTA) scanning speeds (interscan times) on the quantification of choriocapillaris flow deficit percentages (CCFD%) was studied in eyes with nonexudative age-related macular degeneration. We conducted a retrospective review of 30 pairs of scans from 24 age-related macular degeneration subjects enrolled in an ongoing prospective SS-OCTA imaging study. Patients underwent imaging with same day scans at two scanning speeds: 100 kHz and 200 kHz (corresponding with 5.0-ms and 2.5-ms interscan times, respectively). Best practices for CC slab processing and CCFD quantification were implemented, and the compensation level was optimized for each scan. CCFD% measurements were obtained from the 3-mm and 5-mm fovea-centered circles. The mean CCFD% measurements from the 3-mm fovea-centered circles for the 100-kHz and 200-kHz scans were 14.20% and 17.17% respectively, and 10.77% and 12.86% for the 5-mm circles. An agreement analysis showed a significant bias with mean values of 2.96% and 2.09% for the 3-mm and 5-mm circles. The limits of agreement extended predominantly in the positive direction with values of -1.96% to 7.89% and -0.60% to 4.78% in the 3-mm and 5-mm circles, respectively, that emphasize the systematically higher CCFD% recorded using the 200-kHz pattern. No confidence interval for the bias included zero, supporting the significant systematic bias across measurement strategies. SS-OCTA scanning speeds have a significant impact on CCFD% quantification, with slower speeds yielding a lower CCFD%, likely due to the detection of slower CC flow, because of the higher associated interscan times. When following and comparing choriocapillaris flow deficit percentage measurements over time, the same scanning speed should be used at each visit.

Eyes with intermediate age-related macular degeneration (iAMD) underwent swept-source optical coherence tomography angiography (SS-OCTA) imaging and were evaluated longitudinally to determine if choriocapillaris flow deficits (CCFDs) developed before or after the formation of large choroidal hypertransmission defects (hyperTDs). A retrospective review was performed of prospectively collected 6 × 6-mm SS-OCTA images from eyes with iAMD that developed large hyperTDs, defined on en face images from subretinal pigment epithelium (sub-RPE) slabs positioned 64 to 400 µm beneath Bruch's membrane (BM) as bright lesions with a greatest linear dimension (GLD) ≥ 250 µm. The onset of large hyperTDs was designated as baseline T = 0; additional visits were chosen at 1 year before and at two 1-year intervals after T = 0. A grid box strategy was implemented for the analysis of CCFDs at the site where hyperTDs formed. A change in the percentage of CCFDs greater than 5% was considered to be a true change outside the repeatability limits. Twenty-seven targets from 27 eyes eligible for final analysis were followed over four visits separated by 12 ± 3 months. No targets showed a marked CCFD change above 5% prior to hyperTD onset. Only two targets showed marked increases in CCFDs after hyperTD formation. A grouped analysis of all targets showed no mean CCFD change prior to hyperTD onset, but a significant change only after the onset of hyperTD. CCFD values did not increase prior to the onset of hyperTDs with increases in CCFDs detected after their onset. These results suggest that loss of choriocapillaris perfusion did not precede hyperTD formation but may play a role in hyperTD growth.