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Daniel Hammer, Ricardo Villanueva, Anant Agrawal, Osamah Saeedi, Zhuolin Liu; Distribution of inner limiting membrane microglia in glaucoma measured with adaptive optics–optical coherence tomography. Invest. Ophthalmol. Vis. Sci. 2020;61(7):3498.
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© ARVO (1962-2015); The Authors (2016-present)
Microglia primarily reside in three retinal locations: above the inner limiting membrane (ILM) and in the two (inner and outer) plexiform layers. ILM microglia have recently been resolved with adaptive optics (AO) techniques in human subject without the use of extrinsic fluorescence. The purpose of this study is to quantify ILM microglia distribution in subjects with primary open angle glaucoma compared to healthy controls.
ILM microglia were imaged with a multimodal adaptive optics retinal imager [Liu et al., Biomed. Opt. Exp., 9(9), 2018] in four subjects (56.0±5.3 years) with clinically diagnosed glaucoma (severe cases with hemifield defects), five age-matched control subjects (59.7±6.7 years), and three younger control subjects (28.7±5.0 years). With the system focus set to the inner retina, 30 volumes sized 1.5×1.5° were collected from each subject at 17 and 15 non-overlapping regions separated by 1.5° along the horizontal (±12°) and vertical (±10.5°) midline, respectively. The volumes were registered in three dimensions and averaged. Microglia were manually counted and their position recorded. Microglia were determined mainly from three criteria: their appearance (in both ramified and reactive states), position (within 10 µm above ILM), and hyperreflectivity.
Microglia were observed in both ramified and reactive states, the former in a phenotypical appearance with radial probing processes and the latter manifest by an ameboid shape. The density of microglia across the entire horizontal and vertical midlines in the young control, age-matched control, and glaucoma subjects was 36.7±11.4, 3.5±3.5, and 5.9±6.8 mm-2 (average ± standard deviation), respectively. The percentage of microglia within 5° of the fovea was 10±9%, 15±22%, and 46±41% mm-2 for the same groups. Some observable differences in morphological parameters (e.g., process length) are noted in glaucoma compared to control subjects.
ILM microglia density decreases with age. A higher percentage of microglia are present in the central macula region in glaucoma subjects compared to age-matched controls. ILM microglia may serve as a potential biomarker of glaucoma.
This is a 2020 ARVO Annual Meeting abstract.
Figure 1. ILM microglia distribution for (a) young controls, (b) age-matched controls, and (c) glaucoma subjects. Inset shows microglia examples taken from one subject in each group.
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