Development trajectory and trends of ultrasound biomicroscopy in glaucoma research: a comprehensive 20-year bibliometric analysis

Abstract

Purpose

This study conducts a comprehensive bibliometric analysis regarding the application of ultrasound biomicroscopy in glaucoma research over the past two decades.

Methods

Bibliometric analysis was performed on relevant literature published between 2005 and 2024. Data pertaining to authorship, affiliations, countries of origin, journals, keywords, and cited references were extracted. Visualization and analysis were executed utilizing VOSviewer and CiteSpace software.

Results

Bibliometric analysis of 557 articles revealed a quadratic growth trend in annual publication volume. The most productive authors, institutions, countries, and journals were identified and collaboration network maps were drawn. Keyword co-occurrence analysis identified five primary research clusters: angle-closure glaucoma pathogenesis, cataract surgery & complications, glaucoma surgery, ciliary body & iris, and iridocorneal angle. Burst detection and timeline analysis highlighted emerging research frontiers, including deep learning, 3D reconstruction, vitreous zonule imaging, and minimally invasive glaucoma surgery. These findings signal a shift in research priorities towards computational approaches and novel clinical applications.

Conclusion

This bibliometric analysis delineates the dynamic evolution and broadening scope of ultrasound biomicroscopy application in glaucoma research over the past two decades. Collectively, these findings affirm the enduring value of ultrasound biomicroscopy and delineate promising avenues for future investigation.

Introduction

Glaucoma represents a leading cause of irreversible blindness worldwide, characterized predominantly by elevated intraocular pressure and progressive optic neuropathy. Based on distinct anatomical features of the ocular anterior segment, this condition is categorized into two primary forms: primary open-angle glaucoma (POAG) and primary angle-closure glaucoma (PACG). POAG constitutes the most prevalent subtype, particularly in the United States and Western Europe, whereas PACG demonstrates significantly higher incidence rates in China and other Asian nations [1, 2]. The pathophysiological divergence between POAG and PACG manifests primarily in the configuration of the iridocorneal angle and aqueous humor outflow dynamics. PACG is strongly associated with specific anatomical variations, including angle closure, shallow anterior chamber, shortened axial length, and anterior lens displacement. In contrast, POAG typically presents with anterior segment anatomy falling within normative parameters [3]. Consequently, meticulous assessment of anterior segment structures is imperative for accurate glaucoma diagnosis and longitudinal monitoring. The primary objective of anterior segment imaging modalities, such as ultrasound biomicroscopy (UBM) and anterior segment optical coherence tomography (AS-OCT), is to evaluate iridocorneal angle morphology. Compared to gonioscopy, these techniques offer distinct advantages, including enhanced operational efficiency and objective, quantifiable data output [4].

UBM utilizes high-frequency transducers (35–50 MHz) to achieve high-resolution, noninvasive In vivo imaging of anterior ocular segment structures at an axial resolution of 20–50 µm. Unlike optical imaging modalities, acoustic waves exhibit superior tissue penetration, permitting visualization of posterior iris, ciliary body, and anterior vitreous—regions inaccessible to AS-OCT. Consequently, UBM serves as a critical tool for assessing iris-ciliary body tumors and conducting light-and-dark provocative tests in glaucoma diagnosis [5]. UBM has become an essential diagnostic modality in glaucoma management, supporting clinical decision-making, therapeutic evaluation, and scientific investigation [6–8].

Beyond its established role in anterior chamber angle imaging, UBM has been increasingly applied to novel domains within glaucoma research [9–11]. Notably, the integration of deep learning (DL) and computational methodologies for automated UBM image analysis represents a rapidly evolving research frontier [12, 13]. Despite substantial scholarly activity in UBM applications for glaucoma, systematic reviews synthesizing this field remain limited. Given the rapid expansion of relevant publications, quantitative bibliometric approaches are imperative to map research trajectories, identify focal themes, and track emerging trends. This study employs bibliometric analysis to delineate the evolution of UBM in glaucoma research over the past two decades.

Materials and methods

Bibliometric analysis

Bibliometric analysis emerged as a distinct discipline in 1969 [14] and has since been widely adopted as a quantitative methdology for systematic literature review across diverse research fields. This approach integrates bibliographic elements, including authorship, keywords, citations, journal affiliations, institutional collaborations, and national contributions, to map the intellectual trajectory of a discipline and identify its research frontiers. Advancements in computational technologies have further enabled sophisticated visualization of bibliometric networks [15], facilitating the detection of latent relationships among publications and projecting emergent research directions.

Price’s Law and Bradford’s Law are two important laws in bibliometric methods, used to analyze the core contributors and key journals within a field. Price’s Law emphasizes the driving role of a core group of authors in advancing a field [16]. The number of core authors is approximately the square root of the total number of authors, yet they contribute about half of the articles. Mathematically, this relationship is expressed as:

$$\sum _{m+1}^{I}n(x)=\sqrt{N}$$

where: n(x) denotes the number of authors who have produced x articles, I represents the publication count of the most prolific author, m is the threshold for core authorship status, N is the total number of authors.

Bradford’s Law provides the theoretical basis for identifying the core journals in a field [17]. Journals publishing articles in a field can be divided into a core zone and several peripheral zones with gradually decreasing relevance. The number of articles published in each zone is roughly equal, but the proportion of journals follows the ratio: 1:n:n². Conformity to Price’s Law and Bradford’s Law is an important indicator of a research field having formed a mature collaboration network and publication system.

Data source and search process

This study employs the Web of Science Core Collection (WoS CC) as bibliographic source. Recognized for its selective indexing of high-impact journals, robust citation network, and comprehensive interdisciplinary coverage, WoS CC constitutes an optimal data source for bibliometric analysis [18, 19]. The search protocol of this study is outlined in Fig. 1. Following a review of the titles and abstracts, duplicate entries and those considered irrelevant to the research topic were excluded. Each article is independently reviewed by two researchers, and any discrepancies are resolved through discussion. Consequently, 557 articles were selected for inclusion in this study. The complete literature identification and screening workflow is delineated in Fig. 1.

Fig. 1.

Flowchart of the search and bibliometric analysis process for research on the application of UBM in glaucoma research

Data analysis

Data analysis and visualization in this study were performed using VOSviewer (v1.6.20; Leiden University Centre for Science and Technology, Netherlands) and CiteSpace (v6.4.R1; Drexel University, USA) [20]. Additionally, Graphpad Prism (v10.1.12, GraphPad Software, USA) was utilized for the generation of figures.

VOSviewer employs a probability-theory-based normalization method, supporting diverse visualizations of bibliometric entities [21]. In this study, network visualization was primarily utilized to represent bibliometric networks, where node size denotes frequency or centrality, and connection thickness indicates co-occurrence strength. Additionally, the network visualization incorporates a clustering analysis feature, with distinct clusters denoted by different colors. By contrast, CiteSpace adopts a set-theory-driven normalization approach, enabling the generation of time-zone maps, timeline views, heatmaps, and burst detection analyses from bibliometric data. This methodology facilitates the examination of knowledge structure evolution and emergent research trends. Herein, timeline visualization and citation burst analysis were predominantly applied to trace temporal dynamics.

Results

Quantity and annual trends of articles

This bibliometric analysis examined 557 publications drawn from 104 journals. The corpus involves 2325 authors affiliated with 646 institutions across 42 countries. Collectively, these publications cite 8554 references originating from 6050 distinct journals. As depicted in Fig. 2a, the cumulative growth of publications follows a quadratic growth trend (R² = 0.998). Notably, annual output has consistently exceeded 25 articles since 2015, reflecting intensified research focus and highlighting UBM’s critical role in glaucoma diagnosis and management.

Fig. 2.

The descriptive analysis of publications on UBM glaucoma research from 2005 to 2024. a Annual trend of publications. b Cooperation network map of authors with three of more publications. c Cooperation network map of institutions with four of more publications. d Cooperation network map of countries/regions with three of more publications

Bibliometric analysis of authors, organizations, countries/regions and journals

Table 1 lists the top ten most productive authors in this field. Among these core contributors, Aung Tin ranks first with 17 publications over two decades, averaging 38.5 citations per publication. Dada Tanuj follows with 11 publications. Notably, He Mingguang demonstrates the highest citation impact, with 43.6 citations per publication across 10 works. According to Price’s Law, 148 authors with three or more publications are identified as core contributors.

Table 1.

The most important authors, journals, institutions, and countries/regions in UBM glaucoma research

Author	Articles	C/P	Journal	Articles	C/P	Institution	Articles	C/P	Country/region	Articles	C/P
Aung, Tin	17	38.5	J Glaucoma	80	13.7	Sun Yat-sen University	40	20.8	China	191	10.7
Dada, Tanuj	11	35.1	BMC Ophthalmol	32	5.5	Fudan University	26	9.3	USA	125	23.5
He, Mingguang	10	43.6	Eur J Ophthalmol	31	7.2	All India Institute of Medical Sciences New Delhi	21	28.2	India	45	19.9
Gupta, Viney	10	30.7	Ophthalmology	21	51.4	University of California, San Francisco	16	17.1	Japan	35	21.5
Liu, Xing	10	11.2	J Cataract Refr Surg	20	19.1	Singapore National Eye Centre	15	35.2	South Korea	30	11.5
Ritch, Robert	9	26.2	Brit J Ophthalmol	19	28.2	National University of Singapore	15	34.5	Italy	24	15.1
Sun, Xinghuai	9	7.3	Invest Ophth Vis Sci	17	24.7	New York Eye & Ear Infirmary of Mount Sinai	14	26.8	Singapore	22	34.3
Chen, Liming	9	2.7	Eye	14	24.4	Capital Medical University	14	5.4	Switzerland	19	11.5
Tello, Celso	8	28.0	Graef Arch Clin Exp	14	7.9	New York Medical College	12	27.8	England	17	45.4
Wang, Xin	8	12.9	Int J Ophthalmol-Chi	14	4.6	New York University	12	23.4	France	16	15.1

C/P: Citation/Publication.

Author collaboration networks among researchers with three or more publications were analyzed using VOSviewer (Fig. 2b). In the resulting visualization, node size scales with publication volume, connection thickness indicates collaborative intensity, and color coding reflects cluster affiliation. These patterns demonstrate established collaborative frameworks within the UBM glaucoma research domain.

The 646 institutions affiliated with authors of these 557 publications include ten leading contributors detailed in Table 1. Institutional collaboration networks among entities with four or more publications were analyzed using VOSviewer (Fig. 2c). Node size scales with publication volume, while connection intensity indicates collaborative strength. These patterns demonstrate that UBM glaucoma research is predominantly conducted within a limited cohort of institutions, establishing stable partnerships and forming a cohesive research network.

Publications originated from 42 countries/regions, with the top ten contributors detailed in Table 1. Countries/regions with three or more articles were analyzed via visualization (Fig. 2d), revealing significant geographic clustering with research output concentrated among limited countries. China and the United States emerged as core contributors to UBM glaucoma research, exhibiting extensive international collaboration.

A total of 104 journals have published articles on UBM applications in glaucoma research. Table 1 lists the top ten journals by publication volume. According to Bradford's Law, journal classification by publication volume (Table 2) reveals three distinct zones with comparable article counts, while journal quantities conform to Bradford's distribution (n = 4). Journals with 20 or more publications are considered core sources in this field.

Table 2.

The zoning of journals in the field of UBM glaucoma research

Zone	Publication/journal	Journals	Number of publications
Core zone	≥ 20	5	184
Related zone	8–19	17	200
Peripheral zone	1–7	82	173

Hotspots and evolution of keywords

From 557 articles, 1699 keywords were extracted. Based on Price’s Law, keywords with 12 or more occurrences were identified as core keywords for UBM applications in glaucoma research. VOSviewer-generated network visualization (Fig. 3a) reveals keyword co-occurrence patterns, where node size scales with frequency, connecting lines denote co-occurrence relationships, and colors indicate thematic clusters. Beyond “UBM” and “glaucoma”, high-frequency terms include “OCT”, “trabeculectomy”, “anterior segment”, “angle-closure glaucoma”, “ciliary body”, and “phacoemulsification”. Keywords of UBM glaucoma research are classified into five thematic clusters, color-coded in Fig. 3a. Fig. 3b summarizes each cluster’s core themes and representative keywords.

Fig. 3.

Keyword co-occurrence analysis in the field of UBM glaucoma research between 2005 and 2024. a Network map of keywords. b Clusters of keywords

The evolution of keywords over time reflects shifts in research hotspots within a field. We divided the 20-year period into four five-year phases and generated keyword co-occurrence network maps for each phase using CiteSpace. The results are presented in Fig. 4. In these maps, node size represents the frequency of keyword occurrence, while concentric rings within nodes indicate annual occurrence counts, with innermost to outermost rings corresponding to earlier to later years. In Phase 1, UBM glaucoma research primarily focused on the diagnosis of angle-closure glaucoma. During Phase 2, pathogenesis mechanisms such as plateau iris and pupillary block emerged as key research hotspots. In addition, keywords related to glaucoma surgery also began to emerge. By Phase 3, other glaucoma subtypes, including malignant glaucoma and secondary glaucoma, were systematically characterized using UBM. In Phase 4, quantitative studies leveraging UBM imaging gained prominence as a dominant research trend.

Fig. 4.

Keyword co-occurrence map of UBM glaucoma research across different time periods. a Keywords with 5 or more appearances in 153 publications between 2005 and 2009. b Keywords with 4 or more appearances in 99 publications between 2010 and 2014. c Keywords with 6 or more appearances in 152 publications between 2015 and 2019. d Keywords with 7 or more appearances in 182 publications between 2020 and 2024

Keyword burst analysis was conducted on 557 articles using CiteSpace. Fig. 5 illustrates the results, revealing concentrated keyword emergence during 2007–2015. “Laser iridotomy” exhibited the highest burst strength, while “closure glaucoma” sustained the longest burst duration. Current research foci are reflected by “parameters”, “thickness”, and “ciliary body”.

Fig. 5.

Top 20 keywords with the strongest citation burst in the field of UBM glaucoma research

Co-citation analysis

Analysis of 557 articles revealed 8554 referenced sources, reflecting a comprehensive research corpus on UBM applications in glaucoma. CiteSpace-based cluster analysis of these references (Fig. 6) identified 18 thematic clusters, with the most cited being deep learning [22], gonioscopy [23], anterior chamber [24], plateau iris [25], and anterior segment cyst [26].

Fig. 6.

The cluster map of co-cited references in the field of the application of UBM in glaucoma from 2005 to 2024

The most highly cited publications in UBM glaucoma research reflect the enduring scientific priorities in the field. Figure 7 displays the top 20 references with strongest citation bursts. Analysis of the top 20 articles reveals that the therapeutic outcomes of laser peripheral iridotomy (LPI) for PACG constitute the predominant focus [27–31]—a question that remains unresolved to this day. Further prominent topics include the relationship between iris morphology and PACG pathogenesis [23, 25, 26], as well as comparative assessments of AS-OCT and UBM imaging modalities [32, 33]. Notably, recent burst literature identifies malignant glaucoma [34] and quantitative directional analysis of UBM images [22, 35] as emerging research frontiers.

Fig. 7.

Top 20 references with the strongest citation bursts in the field of UBM glaucoma research

Discussion

Summary of research over the past 20 years

In this investigation, bibliometric analysis of 557 UBM glaucoma research articles over two decades reveals significant publication growth, reflecting UBM technological advancements and its increasing diagnostic and therapeutic relevance. This expansion was further driven by rising research funding and institutional academic capacity development.

Prominent contributors, including Aung Tin, Dada Tanuj, and He Mingguang, focus predominantly on PACD pathogenesis [23, 36], diagnosis, and prevention [37, 38]. Authors with three or more publications constitute the core author cohort. The close alignment of the authors with Price’s Law indicates established collaboration patterns in UBM glaucoma research. China, the United States, and India lead in research output volume, while England produces the highest-impact scholarship. Chinese and American scholars drive international collaboration networks, demonstrating extensive partnerships that highlight the critical role of globalized research in leveraging informatics-era advantages.

Five core journals in UBM glaucoma research collectively contribute one-third of relevant publications. Journal of Glaucoma represents a specialized glaucoma journal, while BMC Ophthalmology, European Journal of Ophthalmology, Ophthalmology, and Journal of Cataract and Refractive Surgery constitute broad-scope clinical ophthalmology journals. The high consistency between the article distribution and Bradford’s Law indicates that a mature publication system has been established in the field of UBM glaucoma research. Analysis reveals that highly cited publications in Ophthalmology primarily focus on UBM-based anatomical characterization of glaucoma pathogenesis [23, 39, 40], advancing the understanding of disease mechanisms. This distribution confirms UBM’s primary application in clinical ophthalmology. Future translational studies employing UBM in glaucoma-relevant animal models may elucidate pathogenic mechanisms [41] and accelerate novel therapeutic development [42].

Classic applications of UBM in glaucoma: PACD

Between 2005 and 2014, UBM applications in glaucoma were predominantly centered on PACD, with researchers leveraging UBM to explore its pathogenesis and advance diagnostic and therapeutic strategies.

UBM enables direct assessment of scleral spur morphology, facilitating efficient diagnosis of anterior chamber angle occlusion. UBM further quantifies key anatomical parameters, including anterior chamber depth, iris thickness, and ciliary body dimensions [26, 43], which establish its critical role in PACD diagnosis. While aqueous flow obstruction and iris anterior displacement caused by pupillary block remains a primary pathogenic mechanism in PACD, studies by Cronemberger et al. [44] indicate persistent angle closure post-LPI in 13 PACG patients, suggesting non-pupillary block mechanisms. Notably, PI and anterior lens displacement constitute significant alternative mechanisms [45]. UBM-based analyses reveal that approximately one-third of PACG or primary angle-closure suspect (PACS) cases exhibit PI characteristics [23, 46–48], with no racial variations observed [49]. This finding underscores the importance of PI as an additional mechanism in the pathogenesis of PACD, alongside pupillary block. Diagnostic criteria for PI include iris thickness at 750 μm from scleral spur [50]. Additionally, UBM identifies anteriorly rotated ciliary bodies and anteriorly positioned ciliary processes as angle closure risk factors [51, 52]. The limited circumlental space, defined as the shortest distance between the ciliary process and crystalline lens equator, along with its potential “partial ciliary block” effect, may represent one of the pathogenic mechanisms associated with PACD [53]. Accommodation status may further modulate ciliary body effects on anterior chamber dynamics [54, 55]. Recent studies implicate vitreous zonule abnormalities in PACD pathogenesis: reduced zonule prevalence in angle closure patients may promote vitreous body anterior displacement, exacerbating anterior chamber crowding [9, 56]. Compared with AS-OCT, UBM’s superior posterior segment visualization highlights this mechanism, though the precise role of vitreous zonules requires further investigation.

Extended applications over the last decade: other types of glaucoma

During the second decade, UBM applications extended beyond PACD to diverse glaucoma subtypes. UBM demonstrates significant diagnostic utility in secondary glaucoma (SG). UBM primarily assesses anterior segment tumors, enabling detailed visualization of iridociliary cysts and their structural impacts [57, 58]. It further delineates SG associated with medulloepithelioma and melanoma [59, 60], and evaluates lens subluxation-induced acute angle closure [61]. Certain instances of neovascular glaucoma may present with angle closure, yet exhibit distinct characteristics on UBM, such as the pseudo angle phenomenon and the hockey stick sign [62]. UBM also applies to non-angle-closure SG subtypes. For instance, research by Mora et al. has demonstrated that UBM possesses strong diagnostic capabilities in pigmentary glaucoma [63]. UBM can also enable earlier diagnosis of pseudoexfoliation syndrome through imaging of the lens zonules [64]. In cases of closed globe injuries, UBM can predict the development of chronic traumatic glaucoma by revealing a wider angle and the absence of cyclodialysis [65]. UBM’s high-resolution imaging thus facilitates comprehensive SG pathogenesis investigation. Pending issues in SG subtyping warrant further research, positioning UBM as a critical tool for future SG studies.

The stringent cooperation requirements of UBM limit its applicability in pediatric ophthalmology. Notably, UBM examinations in primary congenital glaucoma (PCG) patients reveal distinct pathological alterations, including abnormal trabecular meshwork membranes and atypical iris-ciliary process insertion [66]. Compared with PACG, PCG exhibits greater heterogeneity in anterior segment structures. Consequently, UBM holds significant potential for PCG diagnosis, clinical management, and pathogenesis research.

Beyond assessing pathogenesis and anterior segment anatomy, UBM plays a critical role in predicting treatment outcomes and postoperative monitoring for glaucoma interventions. LPI effectively widens the anterior chamber angle [37] yet exhibits limited efficacy in resolving peripheral anterior synechiae (PAS) [67]. UBM identifies predictive biomarkers for unfavorable LPI outcomes, including reduced iris curvature, anteriorly positioned ciliary bodies, and basal iris insertion [68, 69]. Furthermore, UBM enables multidimensional assessment of filtration bleb functionality [10, 70]. With the emergence of minimally invasive glaucoma surgery (MIGS), UBM serves as a vital efficacy evaluation tool for novel therapies [7, 71, 72].

Hot topics and development trends: artificial intelligence and 3D reconstruction

Over the past five years, DL has become prominent in glaucoma research utilizing UBM, emerging as a key investigative focus. Shi et al. pioneered DL applications to UBM in 2019, employing convolutional neural networks to classify UBM images into three angle configurations: open, narrow, and closed angles [73]. Subsequent studies expanded DL to quantify anterior chamber angle parameters [12]. Notably, Wang et al.’s model achieved accurate angle closure diagnosis while measuring trabecular-iris angle, angle opening distance, and angle recess area [74]. DL models further demonstrated efficacy in differentiating lens status and locating scleral spurs in UBM images [75–77]. Addressing UBM’s limitations versus AS-OCT, Ye et al. leveraged a cycle-consistent generative adversarial network to synthesize UBM images from AS-OCT data [78]. Kaothanthong et al. later applied this approach to diagnose PI, outperforming direct AS-OCT analysis [79].

In addition to DL applications, 3D imaging techniques enhance UBM research. Minhaz et al. employed 3D reconstruction to transform two-dimensional UBM images into volumetric representations, subsequently utilizing DL algorithms for ciliary body segmentation [13]. This integration of 3D frameworks is poised to significantly advance UBM's imaging precision and diagnostic utility, establishing it as a key research direction in ocular imaging.

Limitations

Bibliometric analysis provides a critical framework for assessing historical evolution, research foci, and developmental trajectories within academic disciplines. However, methodological constraints in this study, including publication timeframe limitations, language restrictions, and database selection criteria, may have omitted significant scholarly contributions. Additionally, bibliometric approaches typically avoid full-text examination, potentially overlooking nuanced methodological details and theoretical complexities. Future research should incorporate broader literature sources and conduct systematic syntheses of methodological specifics to enhance analytical rigor.

Author contributions

Conception and design: Ying Xu, Fengrui Yang, Huijuan Wu. Analysis and interpretation of the data: Ying Xu, Fengrui Yang, Qian Zhang, Yafei Fu. Drafting of the paper: Ying Xu, Fengrui Yang. Revising of the paper: Huijuan Wu. All the authors were involved in the final approval of the version to be published; and all authors agree to be accountable for all aspects of the work.

Funding

This work was supported by Capital’s Funds for Health Improvement and Research (2024–2–4087), Peking University People’s Hospital Research and Development Funds (RDGS2024-06), and the Natural Science Foundation of Beijing (L258058). The funders had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; or decision to submit the manuscript for publication.

Data availability

No datasets were generated or analysed during the current study.

Declarations

Conflict of intrest

The authors have no relevant financial or non-financial interest to disclose.