Journal of Current Glaucoma Practice
Volume 14 | Issue 3 | Year 2020

Evolution of Glaucoma Research: A Scientometric Review

Parul Ichhpujani1, Gagan Kalra2, Rishemjit Kaur3, Shibal Bhartiya4

1,2Department of Ophthalmology, Government Medical College and Hospital, Chandigarh, India
3CSIR-Central Scientific Instruments Organisation, Chandigarh, India
4Glaucoma Facility, Department of Ophthalmology, Fortis Memorial Research Institute, Gurugram, Haryana, India

Corresponding Author: Parul Ichhpujani, Department of Ophthalmology, Government Medical College and Hospital, Chandigarh, India, Phone: +91 9501071591, e-mail:

How to cite this article Ichhpujani P, Kalra G, Kaur R, et al. Evolution of Glaucoma Research: A Scientometric Review. J Curr Glaucoma Pract 2020;14(3):98–105.

Source of support: Nil

Conflict of interest: None


Ophthalmic literature has been subjected to scientometrics in the past both for specific disease pathologies, such as, age-related macular degeneration, glaucoma, and diabetic retinopathy, and specific journals to add insight to the evolving trends. This short scientometric review looks at the distribution pattern and subject domain knowledge of worldwide glaucoma research with data extracted from Web of Science (WoS, Clarivate Analytics) for the past 74 years.

Keywords: Bibliometrics, Citation, Collaboration, Glaucoma, Scientometric analysis.


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.


The current descriptive scientometric study targeted a schematic view of the scientific map in the field of glaucoma. We used a WoS (, 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.


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.

Geographic Metrics

United States of America (USA) (n = 7,605, 23%), China (n = 1,472, 5%), United Kingdom (UK) (n = 1,466, 4%), India (n = 1,375, 4%), and Germany (n = 1,271, 4%) were the highest producing countries among others. Global collaboration network over the period analyzed in the study is represented in Figure 2. The USA has maximum collaborations with China, Brazil, Canada, and Japan whereas India collaborates mostly with Australia, UK, Singapore, etc. Table 1 shows the top 20 country-wise article productivity and collaboration. International collaboration was defined as an article being published by at least two authors with two different country affiliations.

Fig. 1: Annual production trends along with annual average article citation trends

Fig. 2: Global collaboration network over the period of 1945 to 2019

Source Metrics

Hirsch index (h-index) and a total number of citations (TC; average citation count per article) are two important author-level parameters. h-index is a metric that attempts to measure both the productivity and citation impact of the publications of a scientist.

Table 1: Top 20 country-wise article productivity and collaboration
CountryArticlesSCPMCPMCP ratio
China1,4721,221   2510.1705
United Kingdom1,4661,195   2710.1849
India1,3751,167   2080.1513
Germany1,2711,088   1830.1440
Japan1,1071,046    610.0551
Korea   867   782     850.0980
Italy   657   569     880.1339
Canada   552   429   1230.2228
Australia   548   405   1430.2609
France   515   465     500.0971
Turkey   409   399     100.0244
Spain   352   300     520.1477
Switzerland   305   233     720.2361
Singapore   265   138   1270.4792
Brazil   237   204     330.1392
Netherlands   230   186     440.1913
Sweden   207   176     310.1498
Israel   199   166     330.1658
Greece   184   123     610.3315

SCP, single country publication (intracountry); MCP, multiple country publication (intercountry); MCP ratio, refers to MCP as a proportion of total publication number

Ophthalmology (h-index = 125, TC = 70,299), Investigative Ophthalmology and Visual Science (IOVS) (h-index = 107, TC = 49,537), Archives of Ophthalmology (Now, JAMA Ophthalmology) (h-index = 99, TC = 48,594), American Journal of Ophthalmology (AJO) (h-index = 98, TC = 50,184), and British Journal of Ophthalmology (BJO) (h-index = 77, TC = 35,345) were the highest impact sources for glaucoma research among others.

In terms of total article production, IOVS (n = 7,011, 21%), Journal of Glaucoma (n = 1,807, 6%), AJO (n = 1,747, 5%), Ophthalmology (n = 1,412, 4%), and BJO (n = 1,134, 3%) had the greatest number of research items pertaining to our topic of interest.

The top 20 journals in terms of impact along with their number of research items pertaining to glaucoma have been summarized in Table 2.

Bradford’s Law of Scattering

Bradford’s law of scattering helps to identify the core journals relevant to the research field (Fig. 3). It is based on the principle of centric productivity zones, where the journals are divided into different zones having the same number of articles. The core journals are those that contribute to one-third of total publications.2 Top four core journals identified were IOVS, Journal of Glaucoma, AJO, and Ophthalmology.

Author Metrics

Harry Quigley (h-index = 78, TC = 28,237, n = 278, 0.85%), Robert Weinreb (h-index = 68, TC = 16,495, n = 523, 1.6%), Robert Ritch (h-index = 54, TC = 12,607, n = 386, 1.2%), Stephen Drance (h-index = 53, TC = 9,114, n = 175, 0.53%), and Linda M Zangwill (h-index = 51, TC = 6,933, n = 243, 0.74%) were the leading authors by impact among others in the area of study.

The top 10 cited documents, authors, local and global citation count metrics along with other parameters are summarized in Table 3. Table 4 elucidates the author impact of 20 top authors.

Lotka’s Law

This most basic law of bibliometrics deals with the frequency of publications by authors in any given field. It helps to examine the productivity of authors. It states that the relationship between the number of authors and publications follows an inverse square law, which means that most of the authors publish a few papers, while the authors publishing many papers are few. Lotka’s law is given by the following equation:

where Y is the proportion of authors producing X publications, and β coefficient and C are constants specific to the research field. Lotka found that almost 60% of authors make a single contribution and 15% will have two contributions.3

Table 5 shows the observed distribution of publications by authors in the field of glaucoma. It can be observed that 58.3% of authors have published only 1 article, 17.7% have published 2 articles while only 3.6% of authors have produced more than 10 articles. We have estimated the β coefficient of our bibliometric collection using Lotka’s law. The estimated β coefficient was 1.93 (with the goodness of fit = 0.92) and the constant C was 0.361. The p value of 0.008 was obtained by employing the Kolmogorov–Smirnoff two-sample test indicating that there is no significant difference obtained between theoretical Lotka’s and the observed distribution (Fig. 4).

Document Metrics

Global Citation Score (GCS) provides the citation frequency based on the full WoS count at the time the data were downloaded.

Table 2: Journal-wise productivity of top 20 journals
S. no.Journal nameh-Indexg-Indexm-IndexTotal citationsTotal publications
  2Investigative Ophthalmology and Visual Science1071512.4318181818181849,5377,011
  3Archives of Ophthalmology  991831.3026315789473748,5941,068
  4American Journal of Ophthalmology  981551.2894736842105350,1841,747
  5British Journal of Ophthalmology  771401.0131578947368435,3451,134
  6Journal of Glaucoma  65  952.626,1731,807
  7Survey of Ophthalmology  55  871.25  8,689   200
  8Experimental Eye Research  46  690.92  6,350   187
  9Acta Ophthalmologica  43  58  8,574   963
10Graefes Archive for Clinical and Experimental Ophthalmology  43  63  8,396   492
11Eye  41  591.24242424242424  8,552   602
12Molecular Vision  38  501.9  5,977   280
13Acta Ophthalmologica Scandinavica  37  531.42307692307692  4,439   287
14Journal of Cataract and Refractive Surgery  36  601.02857142857143  4,504   214
15Current Opinion in Ophthalmology  36  571.16129032258065  4,077   189
16PLoS One  34  452.61538461538462  4,693   391
17Ophthalmic Surgery and Lasers  34  550.708333333333333  5,054   279
18Clinical and Experimental Ophthalmology  32  45  4,253   553
19Progress in Retinal and Eye Research  32  471.18518518518519  5,435     47
20Human Molecular Genetics  30  501.2  3,862     50

Fig. 3: Bradford’s law

Fig. 4: Lotka’s law

Harry Quigley, 2006 (GCS = 3,379, Country = USA), Michael A Kass, 2002 (GCS = 2,079, Country = USA), Anders Heijl 2002 (GCS = 1,727, Country = Sweden), AGIS 2000 (GCS = 1,625, Country = USA), and Harry Quigley, 1996 (GCS = 1,499, Country = USA) had the greatest number of citations among others from our topic of interest as elucidated in Table 2.

KeyWords Plus and Author Keywords

Universities/Institutes with Significant Contribution

Table 5 enlists the top 20 universities or institutes with a maximum contribution in terms of peer-reviewed, published glaucoma articles.


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

Table 3: Top 10 cited documents, authors, citation count, and author countries
S. No.Author with year of publication and journalTitleType of researchYear of publicationLocal citationsGlobal citationsCountry of corresponding authorDOI link
  1Quigley HA, 2006, Brit J OphthalmolThe number of people with glaucoma worldwide in 2010 and 2020Epidemiological20061,8853,379USA10.1136/bjo.2005.081224
  2Kass MA, 2002, Arch OphthalmolThe Ocular Hypertension Treatment Study, A Randomized Trial Determines That Topical Ocular Hypotensive Medication Delays or Prevents the Onset of Primary Open-Angle GlaucomaClinical20021,2842,079USA
  3Heijl A, 2002, Arch OphthalmolReduction of Intraocular Pressure and Glaucoma Progression, Results from the Early Manifest Glaucoma TrialClinical2002   9901,727Sweden10.1001/archopht.120.10.1268
  4Van Veldhuisen PC, 2000, Am J OphthalmolThe advanced glaucoma intervention study (AGIS): 7. The relationship between control of intraocular pressure and visual field deteriorationClinical2000   8991,625USA
  5QUIGLEY HA, 1996, Brit J OphthalmolNumber of people with glaucoma worldwideEpidemiological1996   8311,499USA10.1136/bjo.80.5.389
  6Gordon MO, 2002, Arch OphthalmolThe Ocular Hypertension Treatment Study, Baseline Factors that Predict the Onset of Primary Open-Angle GlaucomaClinical2002   7981564USA10.1001/archopht.120.6.714
  7Tham YC, 2014, OphthalmologyGlobal prevalence of glaucoma and projections of glaucoma burden through 2040: a systematic review and meta-analysisEpidemiological2014   6641,114Singapore10.1016/j.ophtha.2014.05.013
  8Leske MC, 2003, Arch OphthalmolFactors for glaucoma progression and the effect of treatment: the early manifest glaucoma trialClinical2003   6471,108USA10.1001/archopht.121.1.48
  9Schulzer M, 1998, Am J OphthalmolComparison of glaucomatous progression between untreated patients with normal-tension glaucoma and patients with therapeutically reduced intraocular pressuresClinical1998   598   961Canada
10Stone EM, 1997, ScienceIdentification of a Gene that Causes Primary Open Angle GlaucomaBasic Science1997   5951,004USA10.1126/science.275.5300.668
Table 4: Author impact of top 20 authors
Quigley HA  781671.69628,237278
Weinreb RN  681101.61916,495523
Ritch R  541051.25612,607386
Drance SM  53  930.869  9,114175
Zangwill LM  51  781.962  6,933243
Caprioli J  48  81  7,405265
Medeiros FA  47  782.35  6,943247
Sample PA  46  681.314  4,843125
Liebmann JM  43  671.344  5,535255
Hitchings RA  43  690.956  5,302191
Jonas JB  42  651.273  5,164174
Spaeth GL  41  650.759  5,035219
Friedman DS  41  751.577  5,788145
Flammer J  38  690.927  5,092121
Heijl A  38  880.826  7,904110
Aung T  36  711.565  5,740248
Allingham RR  35  571.061  3,655159
Bengtsson B  35  840.875  7,198  87
Wiggs JL  34  561.172  3,460179
Schuman JS  34  591.1723,683151

h-Index: An author has an h-index of “h” when they have h papers that have been cited h times at least

g-Index: Where the top “g” articles have together received “g” citations

m-Index: h-index divided by the number of years that a scientist has been active

NP, number of publications; TC: total citations

Fig. 5: KeyWords Plus trends for top 11 keywords

Fig. 6: Author keywords trends for top 11 keywords

Table 5: Top universities contributing glaucoma research articles
University/InstituteNo. of glaucoma articles
University of California, San Diego, USA934
Johns Hopkins University, Baltimore, USA840
Duke University, Durham, North Carolina, USA667
Harvard University, Boston, USA577
University Erlangen, Nuremberg, Bavaria, Germany572
University of Michigan, Ann Arbor, Michigan, USA534
L V Prasad Eye Institute, Hyderabad, India527
Moorfields Eye Hospital, London, UK524
University of California, Los Angeles, USA469
All India Institute Med Sciences460
University of Iowa, Iowa City, USA458
University of Toronto, Toronto, Canada439
University of Miami, Coral Gables, Florida, USA421
National University of Singapore, Singapore399
Institute of Ophthalmology394
University of Melbourne, Melbourne, Australia388
University of Sydney, Sydney, Australia369
Fudan University, Shanghai, China366
Columbia University, USA346
Washington University, USA329

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.

Implications and Future Direction

A better understanding of the institutions and researchers focusing on glaucoma research can help researchers plan collaborations, fellowships, and research internships. Analysis of author linkages and the diversity therein must also be encouraged, across continents, to battle the global burden of disease.

It may also be prudent to analyze the reasons for the gender bias in publication and to take remedial measures to circumvent this. A step in this direction could be to encourage gender diversity in active research, as well as in leadership positions and preferential funding and grant allocations.

It is also critical to note that even though the developing world battles the socioeconomic burden of glaucoma blindness more than the developed world, research from these areas is significantly less than from the latter. It, therefore, stands to reason that glaucoma research in these areas must be fostered, both intellectually and financially, so that their issues are better understood and highlighted.

Cross-border mentorship programs and virtual classrooms may well be the way of the future, especially under the aegis of key opinion leaders as identified by the h-index. Across the globe collaborations that share both, the technical know-how and research methodology from premium institutes, with scientists who have access to limited facilities, may well change the face of glaucoma research. This seems more feasible now than ever before, with artificial intelligence and safe electronic data transfers not being limited by geographical boundaries.

A shift to translational research reflects the changing trends, and the current focus on instrumentation in glaucoma practice is demonstrated by the disproportionate number of publications related to diagnostic equipment. While this augers well for disease diagnosis, a similar emphasis on epidemiology and quality of life concerns on management as well as the economic costs of glaucoma therapy may be the future directions for clinician-scientists across the world to focus on.

In addition, analysis of the newer metrics, such as, the download statistics, page ranks, and bookmarking tools such as Mendeley, will add interesting insight to glaucoma research and epistemology.


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