Evolution of Glaucoma Research: A Scientometric Review

INTRODUCTION

Over the years, the concept of glaucoma has evolved from being primarily attributed to elevated intraocular pressure (IOP) to the development of optic neuropathy as the central concept of glaucoma. Despite a vast amount of research, the definition and pathogenesis of glaucoma remains controversial and is still being explored. Analysis of research evolution and research evaluation methodology is as important as the research topics and can be studied using the scientific literature produced in the research field.

Over the years, researchers have coined various terminologies for information and literature analysis, such as, bibliometrics, informetrics, scientometrics, and webometrics.

Bibliometric analysis is based on the identification of the corpus of literature, i.e., exploring multiple aspects of publications (e.g., number of papers, growth of literature), within a given subject area. It studies the relationship between numbers and patterns in bibliographic data, library, and database usage. Scientometrics is a subfield of bibliometrics, which involves the assessment of the impact of research papers and academic journals, the understanding of scientific citations, and the use of such measurements in furthering research in the right direction. Informetrics is a broad term that encompasses modeling, reasoning, and drawing inferences under conditions of noisy and limited information. Webometrics examines different aspects of the web, such as, link analysis, web citation, search engines, etc.

The major scientometric analysis pertaining to glaucoma that we came across had data extracted from the Web of Science (WoS), Institute for Scientific Information (ISI), and mapped 20 years of glaucoma research.¹ In this short scientometric review, we looked at the distribution pattern and subject domain knowledge of worldwide glaucoma research with data extracted from the WoS (Clarivate Analytics) for the past 74 years.

MATERIALS AND METHODS

The current descriptive scientometric study targeted a schematic view of the scientific map in the field of glaucoma. We used a WoS (https://webofknowledge.com), as our database for our analysis on January 1, 2020, using the institutional access (by RK). The term used for the search was chosen in accordance with Medical Subject Heading (Mesh) which is used to index PubMed© contents. Only one parent term (glaucom*) was used. We searched for glaucom* in the title of articles which ensured that the articles relevant to glaucoma research were included in the analysis. We did not search the abstract or introduction or any other section of the article. The “*” is a wildcard that can take any value. The query was done using all the variations of this term for the intended period of January 1945 to January 1, 2020.

The data were exported in BibTeX (.bib) file format. This BibTeX file was further used as the data source in the Bibliometrix R library and biblioshiny app. The retrieved documents included reviews, proceeding papers, letters, editorial material, meeting abstracts, notes, reprints, corrections, news items, book reviews, and additions. Articles about glaucoma were analyzed regarding the topics’ structure, history, and document relationships. Also, the trends in the most influential publications and authors were analyzed.

RESULTS

Our WoS query returned a total of 32,551 documents that were published between 1945 and 2019 and were obtained from 1,906 sources. The total annual production trends along with annual average article citation trends have been summarized in Figure 1.

DISCUSSION

We classified the subject matter of the top-cited articles into broad categories, such as, clinical, epidemiological, basic science, etc. Clinical (6/10) followed by epidemiological (3/10) and basic science research (1/10) formed the top 10 cited articles in our study. This is slightly different from the composition noted by Ramin et al. but generally follows a similar trend.¹

Most of these top-cited articles in our study came from the USA (7/10). Most cited clinical articles generally focused on the control of IOP, risk factor identification, factors affecting treatment, and progression of the disease. This is also reflected in the preferential publication of analytical research involving case-control, cohort, or randomized trials in all of ophthalmology.⁴ Epidemiological research pertaining to glaucoma prevalence were some of the highest cited articles in glaucoma research. Notably, Quigley et al. had two publications in the top-cited articles in glaucoma at the second- and third-highest number of citations as noted by Ramin et al.¹ In our study, these publications have the top and fifth-highest citations, respectively. A relatively recent publication from Tham et al. projected glaucoma prevalence in the world till 2040 and is one of the highest cited glaucoma articles in the short 6 years of its publication.⁵

Here, we would like to highlight that generally, researchers work on a particular research area for some time and their work is extended in multiple articles. While self-citations are used to build over their previous work, they can sometimes be abused for self-promotional activities and increasing the citation impact. However, studies have shown that the self-citations do not impact the macro bibliometrics measure and hence, their exclusion was also deemed unnecessary.^6,7 Also, self-citations have a diminishing impact with time.

More recently, keyword trends in both KeyWords Plus and Author keywords indicate an increasing interest in translational glaucoma research as reflected by an increase in the use of keywords “Optical Coherence Tomography”, “Perimetry”, “Visual Field Testing”, and “Nerve fiber layer”. This is in line with contemporary research albeit over shorter periods.¹ With the advent of advanced imaging and testing techniques, new parallels are being drawn between translational research and clinical ophthalmology resulting in such trends.

It is a common notion that the most cited articles were perhaps published in the most impactful journals. But as our analysis shows, from the top 10 cited articles only one that is the seventh-highest cited article was published in Ophthalmology that was shown to be the highest impact journal in our analysis. Most other articles from our top 10 were published in third-, fourth-, and fifth-highest impact journals. This could be explained by the targeted nature of research conducted in the field of glaucoma within an already specialized branch of ophthalmology where most active researchers look to publish in highly specialized journals, so their work reaches their contemporaries in the field.⁸ Another study published in 2007 showed that the top 100 cited articles at the time were published in Archives of Ophthalmology (now JAMA Ophthalmology), followed by other higher impact journals.⁹

h-index is by far the most accepted metric to analyze the impact of scientific productions, authors, and sources.^10,11 Most impactful authors in our study did not necessarily have the highest number of publications and vice versa. Notably, Harry Quigley had the highest h-index of 78 with a total of 278 publications, Robert Weinreb had the second-highest h-index of 68 with a total of 523 publications and Ritch had the third-highest h-index of 54 with 386 publications. Bengtsson appeared in our top 20 impactful authors with 87 publications while no other author on our top 20 had <110 publications. Also, the greatest number of author citations did not always reflect on the most author impact. For example, Spaeth and Freidman have the same h-index while Friedman has been more frequently cited.

Although the length of the scientific career of an author influences the h-index, and may at times put newcomers at a disadvantage, additional citation parameters such as g-index, can help overcome the limitations of the h-index.

A report released by the National Eye Institute in 2012 identified certain key areas of research development in glaucoma including newer diagnostic and imaging techniques, glaucoma prevalence estimation, new IOP control therapies, ganglion cell loss as an underlying mechanism for glaucoma, genetic basis of glaucoma, novel therapeutics and anterior segment signaling pathways.¹² Our study highlights similar upcoming and prevalent topics over the several years of glaucoma research while being concurrent with past contemporary studies conducted over shorter time durations.¹ Expanding upon earlier findings, our study also showcases current trends in glaucoma research over the recent decade.

Another notable finding was that there were only three female authors among the top 20 authors. Although female presence has grown steadily in the past few decades, women still face many obstacles.

Literature databases viz., PubMed, Scopus, Google Scholar, and WoS differ in terms of their focus and coverage. One of the limitations of our study is that we used only one database, WoS, for collecting data. In our defense, we had institutional access for WoS and it offers a wider coverage and output as compared to PubMed.

REFERENCES

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