In a study published in the Journal of Clinical Medicine, researchers used swept-source and en-face optical coherence tomography angiography images to investigate the morphological changes and density of macrophage-like cells located in the vitreoretinal interface in retinal vein occlusion-affected eyes.
Retinal Vein Occlusion
Retinal vein occlusion (RVO) is the blockage of the retina veins. It is commonly caused by artery hardening and blood clot formation. Retinal vein occlusion, including the central and branch type, is a common cause of vision impairment.
Branch and central retinal vein occlusion can lead to internal retinal area's focal atrophy, especially in the retinal nerve fiber layer and the retinal ganglion cells. RVO causes hypoxia and ischemia in retinal tissue, followed by inflammation involving macrophage-like cells (MLCs) such as microglia and hyalocytes.
Significance of the Macrophage-Like Cells in the Clinical Setting
Microglia are specialized immune cells from the monocyte-macrophage system that perform a key role in the retina's immune system. Microglia also maintain the inner blood-retina barrier.
Macrophage cells in the vitreous fluid are commonly known as hyalocytes. Hyalocytes have been speculated to be one of the biological sources of vascular endothelial growth factors in exudative age-related macular degeneration and diabetic retinopathy.
Earlier research revealed that hyalocytes and microglia were both active in retinal pathology and significantly impacted many retinal diseases, including uveitis, idiopathic epiretinal membrane, and glaucoma. However, these studies used animal models and identified these cells using confocal and staining imaging.
Recent studies claim that macrophages at the internal limiting membranes have been effectively and reliably seen in living human retinas and may have a role in the pathophysiology of RVO.
Investigating MLCs is beneficial for understanding their pathogenesis and identifying therapeutic targets for RVO-related problems.
Using Optical Coherence Tomography to Investigate Macrophage-Like Cell Density
Researchers hypothesized that macrophages were engaged in the pathogenic process of RVO based on the human retina specimen's data and their investigations of RVO in animal models.
Through clinical swept-source OCT and swept-source OCT angiography, the distribution characteristics, morphology, and quantity of MLCs were observed in treatment-naïve and new-onset RVO patients and long-course treated RVO patients.
The research comprised 64 healthy eyes in the control group and 72 RVO patients, consisting of 43 acute and 29 chronic cases in the experimental group. After semi-automatic quantification and binarization, the MLC density and count of the study groups were compared. Lastly, the MLC distribution and density related to retinal edema were evaluated.
Important Findings of the Study
Swept-source OCT angiography is a simple and viable method for characterizing MLCs at the retinal, vitreous interface. A substantial increase in the MLC density in chronic and acute eyes implicates the recruitment and activation of MLCs in RVO.
The MLC distribution and density can be influenced by retinal edema. The congregation and morphological changes of MLCs were observed in RVO eyes.
The chronic and acute groups had increased MLC densities compared to healthy eyes. However, the edematous region's MLC density was lower in the acute group compared to the non-edematous region.
The thickness of the central fovea in acute RVO eyes was negatively correlated with MLC density. However, the situation is considerably different with chronic eyes as the MLC density was positively correlated to the central fovea's thickness and the retina's average thickness in chronic RVO eyes.
Although there were fewer MLCs in the edematous area in the chronic eyes, this was not statistically significant compared to the MLCs density in the whole image.
This study offers clinical evidence that MLCs contribute to RVO diseases, retinal edema, and inflammatory responses.
Due to the limitations of clinical OCT, MLC structural changes in RVO could not be quantified. This study was cross-sectional retrospective research. Therefore, prospective research is needed to demonstrate MLC changes throughout the disease.
After discarding eight eyes with irrelevant disorders, the study included only 62 additional eyes, which may have resulted in a selection bias. The number of instances in each subgroup was inadequate; therefore, observation points were not unified.
The impact of system variables, including hyperlipidemia, hypertension, rheumatism, and drug intake that could impact the result, were not investigated due to inadequate data.
Therefore, clinical observation alone is insufficient to explain the function and origin of these cells. Additional experimental research is needed to investigate the mechanism of this phenomenon.
Wang, W., Sun, G., He, L., & Chen, C. (2022) Increased Macrophage-like Cell Density in Retinal Vein Occlusion as Characterized by en Face Optical Coherence Tomography. Journal of Clinical Medicine. https://www.mdpi.com/2077-0383/11/19/5636/htm