Calcified Deposits and Drusen Biogenesis
Ophthalmology Science, September 2021
In previous research, small spherules formed of hydroxyapatite or whitlockite have been found within deposits that accumulate in the sub–RPE-BL space, which is located between the basal lamina (BL) of retinal pigment epithelium (RPE) and the inner collagenous layer of Bruch membrane. As it has been theorized that these calcified deposits play a role in drusen biogenesis, Pilgrim et al. set out to gain a better understanding of the spherules’ morphology, structure, and distribution in human eyes with and without signs of age-related macular degeneration (AMD). They found that eyes with clinical signs of AMD had more spherules—and larger spherules—than did those without the disease.
For this experimental study, the researchers obtained five cadaveric eyes with varying degrees of sub–RPE-BL deposits. Two of the five eyes were reported as having clinical indications of AMD, while three were considered healthy. The eyes had been enucleated from older patients (range, 69-91 years).
The researchers used three high-resolution imaging methodologies (scanning electron microscopy, energy-dispersive X-ray spectroscopy, and time-of-flight–secondary mass spectrometry) to evaluate the tissue samples. Main outcome measures included the spherules’ surface topography, internal structure, distribution, and average diameter.
Results indicated that the spherules’ surface topography and internal structure varied significantly, and they were ubiquitous across the central axis and mid- and far-peripheral axis of the eyes. Two eyes with signs of AMD had more spherules, and the median diameter of the spherules noted in those eyes was larger than those noted in the healthy eyes (1.64 µm vs. 1.16 µm, respectively).
Understanding the differences in the microenvironment that might exist between healthy and affected eyes could potentially shed light on disease onset or progression, the authors said. This study’s small sample size presented several limitations, they noted, and future research should include a larger cohort of eyes. In addition, better tissue preservation methods are needed, to facilitate better detection of the spherules’ anatomical features.
The original article can be found here.