Individuals over the age of 60 in developed countries are most commonly afflicted with AMD, which is the foremost cause of permanent vision loss [2]. The most prevalent form of AMD is dry AMD, which has the propensity to progress to neovascular or "wet" AMD. This type of AMD is distinguished by the emergence of central choroidal neovascular membranes (CNV), which can cause retinal hemorrhaging and exudation, ultimately resulting in profound vision loss [1]. Zinkernagel et al [27] reported that modifications in the intestinal microbiome are associated with AMD. Some types of gut metagenome in patients with AMD were relatively enriched, such as the genera Anaerotruncus and Oscillibacter as well as Ruminococcus torques and Eubacterium ventriosumand, whereas Bacteroides eggerthii was enriched in controls. Despite this, the frequency of Oscillospira, Blautia, and Dorea was lower among subjects with AMD when contrasted with those who were considered healthy controls [28, 29]. The previously mentioned research provides crucial links between changes in the gut microbiome and the development of AMD. The comprehension of the mechanisms connecting the incidence of AMD with the interactions occurring within the gut microbiota could prove advantageous in the search for methods to avert additional vision loss. However, the causal effects of gut microbiota on AMD remain unclear.
Following the implementation of IVW and sensitivity analysis filtration, it was determined that two distinct taxa were responsible for causing AMD. Genus-Candidatus_Soleaferrea was a protective factor for AMD, while Genus-Faecalibacterium correlated with AMD risk. Ongoing investigations propose the existence of a connection between the gut and eyes, whereby disruptions in gut microbiota could be a pivotal factor in the emergence and escalation of multiple eye disorders, including AMD [30]. As the pathogenesis of AMD is not fully comprehended, and the available treatments are limited, exploring the correlations between modifications in the gut microbiota and AMD could present a plausible avenue for further interventions in the management of AMD.
The research conducted by Cai et al. revealed a positive correlation between the abundance of Candidatus_Soleaferrea and the glucagon-like peptide 2 (GLP-2) [31]. The maintenance of intestinal epithelial morphology and function is facilitated by GLP-2, a trophic hormone that is secreted by the gut microbiota's metabolites, specifically SCFAs [31]. It has been noted that the genus possesses the ability to secrete metabolites that have anti-inflammatory properties and safeguard gut homeostasis [32].
Faecalibacterium is a member of the Clostridium leptum group and is one of the predominant species observed in the gastrointestinal microbiota of healthy adult individuals [33, 34]. Some studies reported the ability of Faecalibacterium strains to produce anti-inflammatory metabolites, including butyrate [35], peptides [36], and an extracellular polymeric matrix [37], showing anti-inflammatory activity both in vitro and in animal models [38]. De Filippis et al. conducted a study on the diversity of Faecalibacterium in the gastrointestinal tracts of humans and animals [39]. Their findings suggest that Faecalibacterium diversity is influenced by various factors such as age, lifestyle, geography, and disease [39].
The study also has several limitations. First, the mechanism of gut microbiota on AMD has not yet been fully elucidated. Furthermore, although the MR approach is successful in establishing causal inference, it is imperative to corroborate its results through randomized controlled trials.