Choriocapillaris Flow Signal Deficits Associated With AMD Severity

The severity of age-related macular degeneration (AMD) and impaired vision is associated with choriocapillaris flow signal deficits (FD%) in patients aged 60 years and older, according to new findings. The study published in Investigative Ophthalmology & Visual Science also found that photoreceptor sustenance may be impaired due to reduced metabolic transport and exchange in the choriocapillaris–Bruch membrane retinal pigment epithelium complex.

AMD is a cause of legal blindness in older adults globally. The histologic attenuation of the choriocapillaris, which is the innermost layer of the eye’s choroid underneath the Bruch membrane, is a staple of aging and AMD. The choriocapillaris provides approximately 90% of the oxygen requirement for photoreceptors. The delayed return of light sensitivity by the rod photoreceptors (rod-mediated dark adaption [RMDA]) is one of the first risk factors seen for the onset of AMD. This study evaluated the relationship between optical coherence tomography angiography (OCTA) and visual function in normal eyes and those that were diagnosed with early AMD or intermediate AMD.

Eye of senior woman | Image credit: Syda Productions - stock.adobe.com

The Alabama Study on Early Age-Related Macular Degeneration 2 was used for baseline data. The Callahan Eye Hospital at the University of Alabama at Birmingham was the location for recruitment of patients 60 years and older between October 2019 and September 2021. Patients were identified as having early or intermediate AMD using the electronic health record. Participants were excluded if they had an eye condition or disease in either eye that could impair vision, had a neurological condition that could impair vision or judgment, had a psychiatric disorder that prevented them from following directions, had diabetes, or had any medical condition that could cause frailty.

The eye with better visual acuity was used for imaging and testing visual function, and 2 OCTA volumes were captured for each study eye. All scans were batch processed. Vision tests for photopic, mesopic, and scotopic conditions were administered. The FD% outcome represents the percentage of pixel areas lacking a detectable flow signal.

There were 410 eyes from 410 participants included in this study; the cohort had a mean (SD) age of 71.7 (5.9) years, 59.8% were women, and 92.0% reported being non-Hispanic White. After classification, 47.8% were older normal eyes, 29.8% were early AMD eyes, and 22.4% were intermediate AMD eyes. The test-retest repeatability of choriocapillaris FD% was good (intraclass correlation coefficient [ICC] = 0.96). There were no significant differences before and after compensation when it came to choriocapillaris FD% quantification (ICC = 0.996). In 20 eyes with drusen, the mean (SD) difference in FD% (drusen vs excluding drusen) was negligible (–0.58 [0.74]).

FD% in early and intermediate AMD was significantly worse compared with older normal eyes. Older normal eyes had a mean (SD) FD% of 52.1% (5.3), early AMD had a mean (SD) of 54.0% (5.5), and intermediate AMD had a mean (SD) of 59.8% (7.4). Choriocapillaris FD% was found to be higher in women (55.1% [6.3]) compared with men (53.3% [6.9]). Current/former smokers also had a higher mean (SD) FD% at 55.9% (7.0) compared with never smokers at 53.3% (6.1). The difference in FD% in normal eyes compared with early AMD eyes was not significant, but intermediate AMD eyes had higher FD% than both.

Greater flow signal deficits were found in early and intermediate AMD eyes compared with normal eyes, with exacerbation in intermediate AMD eyes. All visual functions were significantly worse in eyes with intermediate AMD; RMDA was the only function that was significantly worse between early AMD and normal eyes. Greater FD% was associated with worse vision in all tests barring photopic and mesopic light sensitivity.

There were some limitations to this study. Flow signal attenuation is possible in choriocapillaris OCTA slabs imaged using a spectral domain device. Spectral domain OCTA devices have shorter wavelength compared with other devices that study choriocapillaris. Absolute choriocapillaris FD% cannot be compared using different devices. Devices are constrained by underlying technology, and axial length was not measured to correct lateral scaling.

Worse AMD disease severity and visual impairment, including RMDA, were associated with the loss of choriocapillaris flow signal in adults 60 years and older, the researchers concluded. Identifying the structural biomarkers of early AMD, which affects 18 million individuals in the United States, could help retinal specialists detect eyes at risk for progression.

Reference

Kar D, Corradetti G, Swain TA, et al. Choriocapillaris impairment is associated with delayed rod-mediated dark adaptation in age-related macular degeneration. Invest Ophthalmol Vis Sci. 2023;64(12):41. doi:10.1167/iovs.64.12.41