Research progress on meibomian gland dysfunction from 2011 to 2020: a bibliometric and visualized analysis


 Background

To explore the research areas, hotspots, and progress of meibomian gland dysfunction through bibliometrics.
Methods

Related publications were retrieved from the Web of Science Core Collection from 2011 to 2020. VOSviewer1.6.16, Citespace.5.7.R2, and GraphPad Prism 8 were used to visualize the distribution of countries, research institutions, journals, authors, keywords, and annual publication numbers in this field.
Results

A total number of 716 relevant publications were retrieved. The United States and Keio University ranked the first among the countries and organizations with the most publications. Cornea, Investigative Ophthalmology & Visual Science, and Ocular Surface were the top three journals with the highest publication counts and citations. The authors who contributed to this topic mainly formed three clusters which manifested the research areas, and the extracted keywords mainly formed four clusters which manifested the hotspots were explored.
Conclusions

The research areas and hotspots of meibomian gland dysfunction were as follow: (1) Pathogenesis or potential etiology of meibomian gland dysfunction; (2) Diagnosis of meibomian gland dysfunction; (3) Therapy of meibomian gland dysfunction and the International Workshop`s dedication to it; (4) Epidemiology of meibomian gland dysfunction.


Introduction 22
The meibomian glands, located in parallel rows on the upper and lower eyelids, play a vital role 23 in ocular surface health. The meibum secreted by the meibomian gland comprises the lipid layer of 24 the tear film, which prevents tear evaporation and protects the ocular surface [1]. Meibomian gland 25 dysfunction (MGD) is a diffuse, chronic disorder of the meibomian glands that is characterized by 26 quantitative/qualitative changes in glandular secretion and/or terminal duct obstruction [2]. The 27 International Workshop on MGD, launched by the Tear Film and Ocular Surface Society in 2011 [3], 28 aimed to raise concerns about MGD and accelerate its study. 29 Bibliometrics, also called bibliometric analysis, is a scientific process that analyzes large 30 amounts of literature using statistical methods to reveal the development of specified fields [4]. VOSviewer, exploited by van Eck and Waltman of Leiden University, is a visualization tool for 32 constructing bibliometric networks [5]. Similarly, Citespace, developed by Chaomei Chen, is a Java 33 application for visualizing patterns in scientific literature [6]. Both VOSviewer and Citespace are 34 scientific mapping tools that directly provide visualizes of specified terms and their links. 35 The growing interest in MGD research has resulted in hundreds of publications in recent decades. 36 Considering the substantial number of publications related to MGD, it is difficult to identify the 37 progress and trends in MGD studies. Thus, applying scientific methods to quantitatively and 38 qualitatively assess these publications will be helpful for potential cooperation, further research, and 39 potential publications related to MGD. However, bibliometric studies in the field of MGD are lacking. 40 Therefore, this study performed bibliometric analysis and utilized visualization tools to 41 comprehensively and objectively evaluate MGD studies to reveal the research areas, hotspots, and 42 progress in this field in recent decades.  Tables 2 and 3. Furthermore, 51 to explore the latent connections among them, network maps with nodes and lines were sketched using 52 Citespace. In this study, the nodes represented the analysis components, with their sizes proportional 53 to the weight of the items. The line thickness and length between nodes were proportional to the 54 strength of the relationship between the analysis components. In addition, each term had a 55 corresponding centrality value, in which the terms with the highest values had the core positions in 56 the network and were circled in purple in the figure. As shown in Figure 1b

Journal analysis and highly cited publications 77
The retrieved publications on MGD were identified in 142 journals. Among them, Cornea had the 78 highest number of publications on this topic (93, 12.99%), followed by Investigative Ophthalmology 79 & Visual Science (68, 9.50%) and Ocular Surface (51, 7.12%). The top 10 journals and their impact 80 factors are listed in Table 4. 81

Author analysis 88
Authorship analysis revealed that 2,559 authors had contributed to MGD research. The top 10 89 authors are listed in Table 5. VOSviewer was used to visualize the connections between the authors, 90 which showed three clusters of different colors (Figure 2). The sizes of the nodes corresponded to the 91 number of publications, while the lines between them represent the closeness of the authors. Authors 92 in the same cluster were considered to have a closer connection and cooperation with each other. 93 According to the relevant literature of the leading authors, the research areas of them were as follows.  total authors, 21 met the criteria of more than 10 related publications. Among these, three clusters 123 (cluster 1: red, cluster 2: green, cluster 3: blue) were observed, in which authors with closer 124 connections and cooperation were placed in the same cluster. 125

Analysis of keywords co-occurrence 126
A total of 2,263 keywords related to MGD were retrieved. VOSviewer was used to visualize the 127 keywords appearing with the highest frequencies. The keyword co-occurrence map comprised four 128 different clusters shown in different colors (Figure 3). Keywords in the same color were assigned to 129 the same cluster, with the different clusters indicating research hotspots. The clusters were as follows: 130 Cluster 1 (red), Cluster 2 (green), Cluster 3 (blue), and Cluster 4 (yellow). Ten representative keywords 131 and their occurrences in each cluster are shown in Table 6. 132 keywords, 78 met the minimum frequency of more than 10. The co-occurrence analysis identified four 135 keyword clusters: cluster 1 (red), cluster 2 (green), cluster 3 (blue), and cluster 4 (yellow). 136  (14) keratography (10) topical azithromycin (12) questionnaire (10) tear osmolarity(14) reliability (10) cytokines (10) impact (10)

Discussion 138
This is the first study to report the bibliometric analysis and visualized results of research on 139 MGD. The results of the present study provided a general view of the research progress and trends 140 related to MGD over the last decade. 141

Worldwide tendencies in MGD research. 142
As shown in Figure 1a  Cluster 4 revealed MGD epidemiology, with extracted keywords including "prevalence," 217 "epidemiology," "population" and "risk factors." The growing concern regarding MGD has also 218 emphasized its prevalence. A recent study reported an MGD prevalence of 35 and migraine headaches. In general, MGD has a high prevalence and is prone to affect the population 226 with these risk factors. 227

Conclusions 228
This is the first study to apply scientific methods to evaluate MGD progress and trends in the last 229 decade and identify research hotspots. These research hotspots included the MGD pathogenesis or 230 potential etiology, diagnosis, epidemiology, and therapy, as well as the International Workshop's 231 dedication to MGD. In addition, this study raised the possibility for researchers and ophthalmologists 232 to find further cooperation. 233

Data collection and retrieval strategy 235
All data were collected from the Web of Science Core Collection (WoSCC) using the retrieval 236 strategy: (1) TS (Themes)= "meibomian gland dysfunction"; (2) Time horizon: "from 2011 to 2020"; 237 (3) Document type: "article". A total of 716 publications meeting the criteria with "full record and 238 cited references" were downloaded and saved as "plain text" for the following visualized analysis. 239

Visualized analysis 240
The visualized analysis in this study applied GraphPad Prism 8, VOSviewer1.6.16, and 241 Citespace.5.7.R2 as described previously [47]. GraphPad Prism is a drawing tool widely used in 242 scientific research. The free applications VOSviewer (www.vosviewer.com) and Citespace 243 (https://sourceforge.net/) were used for the visualization analysis of publications, institutions, 244 countries, journals, authors, and keyword co-occurrence in sequence. On the basis of visual analysis, 245 further literature retrieval of partial clustering results was carried out to clarify the research fields and 246 hotspots. 247