Application of ultrasound biomicroscopy in ocular trauma caused by chestnut-burr spines

Abstract

To evaluate the clinical utility of Ultrasound Biomicroscopy (UBM) in diagnosing and managing ocular injuries caused by chestnut-burr spines, particularly for detecting non-metallic scleral foreign bodies and monitoring postoperative inflammatory progression. A retrospective study was conducted on 36 patients (36 eyes) presenting with non-penetrating ocular trauma from chestnut-burr spines. All patients underwent preoperative UBM for foreign body localization and assessment of scleral inflammation. The UBM data obtained at 1 week, 1 month, and 3 months postoperatively were analyzed to assess the changes in scleral thickness and inflammation progression. UBM preoperatively detected foreign bodies in 94.4% cases. Microbial analysis confirmed fungal infection in 52.8% of cases, necessitating antifungal therapy. Preoperative UBM demonstrated scleral thickening (789.7 ± 200.8 μm), which peaked at 1 month post-surgery (965.7 ± 385.2 μm) and subsequently normalized by 3 months (570.4 ± 119.3 μm). Four cases of severe scleral abscess required secondary interventions. UBM demonstrates high diagnostic accuracy in chestnut-burr-related ocular injuries, enabling precise surgical planning and longitudinal, quantitative monitoring of scleral inflammation. It is particularly valuable for identifying non-metallic foreign bodies missed by conventional imaging modalities.

Introduction

Chestnut trees, prevalent in the temperate Northern Hemisphere including China, produce edible nuts encased in spiny burrs. Upon accidental ocular contact, these sharp spines can cause severe injury¹. Ocular trauma from chestnut-burr spines poses significant clinical challenges due to the small size of the spines (<1 mm in diameter) and the high risk of severe complications, including corneal and lens injury, fungal keratitis, fungal scleritis, endophthalmitis, scleral abscess, and recently reported uveal effusion syndrome^2–4. These plant-derived foreign bodies often carry pathogenic fungi (e.g., Alternaria alternata, Fusarium species), which can exacerbate inflammation and delay healing, even after surgical removal. An annual cluster of over ten severe ocular injuries caused by chestnut-burr spines is typically observed at our hospital during the harvest season (September and October), underscoring the clinical relevance of this condition.

Conventional imaging modalities have critical limitations in diagnosing these injuries. Computed tomography (CT) with standard 1-mm slice thickness is limited by partial volume effects and poor soft-tissue contrast, rendering it unreliable for detecting plant-based foreign bodies smaller than 1 mm in diameter. Thin-slice CT (0.5 mm) has low sensitivity for dry wood (with Hounsfield units approximating − 150 to − 371 HU, similar to air or fat) and is isodense to ocular tissue for wet wood, making differentiation difficult. Furthermore, its resolution is often insufficient for fragments smaller than 0.5 mm, a common size for residual chestnut spines⁵. Even with 0.5-mm thin-section scanning, the missed diagnosis rate for chestnut spines remains high, particularly when they are clustered or embedded in the sclera⁶. Magnetic resonance imaging (MRI), while offering superior soft-tissue contrast, is insensitive to materials with low water content such as dry plant matter⁷. The detection threshold for wood on MRI is approximately 0.5–2 mm, but for thin, desiccated chestnut spines (often < 0.5 mm), signal generation is minimal, appearing as indeterminate low-signal areas on T1- and T2-weighted images, indistinguishable from surrounding tissues.

Anterior segment optical coherence tomography (AS-OCT) has significant limitations in the setting of marked conjunctival edema—common in these injuries—where signal scattering and attenuation severely degrade image quality at depth⁸. While AS-OCT remains excellent for corneal lesions, it lacks sufficient penetration depth to adequately visualize scleral or ciliary body involvement^9,10.  Traditional B-scan ultrasonography, widely used for posterior segment foreign bodies, cannot reliably distinguish small anterior segment foreign bodies (e.g., conjunctival or scleral spines) from surrounding tissues due to its low axial resolution (≤ 10 MHz)¹¹. This diagnostic gap often leads to delayed treatment and increased reoperation rates.

Ultrasound biomicroscopy (UBM), operating at higher frequencies (typically 35–100 MHz), overcomes these limitations by providing ultra-high resolution and deeper penetration (4–5 mm), enabling clear visualization of anterior non-metallic foreign bodies and assessment of scleral and ciliary body involvement¹². Its ability to distinguish echogenic spines through characteristic “comet tail” artifacts and acoustic shadows significantly enhances diagnostic accuracy, particularly for occult spines^13–15. Beyond preoperative localization, UBM plays a pivotal role in postoperative monitoring by quantifying dynamic changes in scleral inflammation. This study aims to evaluate the dual role of UBM in (1) the preoperative localization of chestnut-burr spines and (2) the quantitative monitoring of post-removal scleral inflammation—a previously uncharacterized aspect of the healing dynamics in these injuries.

Materials and methods

Study design and participants

We conducted a single-center, retrospective cohort study of consecutive patients presenting with chestnut-burr-related ocular injury at Qingdao Eye Hospital of Shandong First Medical University, between October 1, 2019, and October 31, 2024. The study adhered to the tenets of the Declaration of Helsinki and was approved by the Institutional Ethics Committee (Approval No. 202544). Informed consent was obtained from all participants. The inclusion criteria were: (1) a documented history of ocular trauma attributable to chestnut spines; (2) complete medical records; and (3) scheduled follow-up examinations every 1–4 weeks for at least 3 months, including serial UBM imaging. Patients with incomplete follow-up or missing UBM data were excluded.

Baseline data collection

Demographic and clinical data, including age, sex, occupation, time elapsed since injury, and prior treatments, were collected from medical records. We acquired slit-lamp biomicroscopic photographs with a HAAG-STREIT BX900 and UBM using a SUOER SW-3200 system equipped with a 35 MHz transducer, which provided a 5 mm × 5 mm field of view and 50 μm axial resolution.

UBM protocol for foreign-body detection and measurement

All patients underwent standardized quadrant scanning (3-, 6-, 9-, and 12-o’clock positions), supplemented by targeted high-resolution imaging of areas with conjunctival elevation. Each detected foreign body was documented according to its clock-hour meridian, distance from the scleral limbus, and implantation depth. Scleral thickness was measured at the thickest point adjacent to the foreign body, with triplicate scans averaged for accuracy.

Microbiology and histopathology

Intraoperative specimens were processed for: (1) fungal examination (10% KOH smear; Sabouraud Dextrose Agar culture at 25–28 °C for 1 week); (2) bacterial culture (Gram stain; inoculation in broth followed by blood agar at 37 °C/5% CO₂); and (3) histopathological analysis (10% neutral buffered formalin fixation, paraffin embedding, Hematoxylin & Eosin, and Periodic acid–Schiff staining).

Follow-up

All slit-lamp photographs and UBM images obtained for the enrolled patients were retrospectively reviewed. UBM data from 1 week (5–10 days), 1 month (25–35 days), and 3 months (80–100 days) postoperatively were analyzed. Scleral thickness was measured on every available UBM image acquired throughout the follow-up period to assess the changes in scleral thickness and the progression of inflammation.

Statistical analysis

Data analysis was performed using SPSS 26.0 software (SPSS Inc., Chicago, IL, USA). Continuous variables are expressed as mean ± standard deviation, and categorical variables as numbers (percentages). The specific statistical methods were applied as follows: McNemar’s test was used to compare detection rates between slit-lamp examination and UBM; independent-samples t-test (with Levene’s test for equality of variances) was used to compare continuous variables between two independent groups (e.g., the interval from injury to presentation between the scleral abscess and non-abscess groups, as well as the depth from the conjunctival surface and the overlying conjunctival thickness between slit-lamp-visible and occult foreign body groups); one-way repeated-measures ANOVA with Bonferroni post-hoc testing was utilized to analyze scleral thickness changes across different time points. A two-tailed P-value < 0.05 was considered statistically significant.

Results

Patient demographics

Thirty-six consecutive patients (27 male, 9 female) with chestnut-burr-related ocular trauma were enrolled. The demographic, clinical, and initial management characteristics of the cohort are summarized in Table 1. The mean age was 54.1 ± 9.5 years (range 32–70 years). Most patients (32/36, 88.9%) were farmers. Three patients had undergone incomplete foreign body removal with anti-inflammatory therapy at local hospitals prior to referral, without UBM evaluation; all three cases showed residual spines upon our examination and underwent subsequent surgical removal. Notably, these prior interventions had only addressed superficially visible spines under slit-lamp examination, without scleral exploration. Two additional cases had received anti-inflammatory treatment alone, without attempted foreign body removal.

Table 1.

Demographic, clinical, and diagnostic characteristics of patients with ocular trauma from chestnut-burr spines (n = 36).

Characteristic	Value
Demographics
Male-to-female ratio (M: F)	27:9
Mean age (years)	54.1 ± 9.5 (range 32–70)
Time to presentation (days)	21.6 ± 16.4 (range 1–70)
Uncomplicated scleritis group	18.5 ± 13.1
Scleral abscess group	46.5 ± 21.4
Foreign body profile
Localization, n (%)
Conjunctiva	3 (8.3%)
Sclera	33 (91.7%)
Multiplicity, n (%)
Single spine	23 (63.9%)
Multiple spines (2–4)	13 (36.1%)
Treatment history
Initial treatment at our center, n (%)	5 (13.9%)
Referred cases, n (%)	31 (86.1%)
Diagnostic and surgical outcomes
Slit-lamp detection rate, n (%)	12 (33.3%)
Initial UBM detection rate, n (%)	34 (94.4%)
Microbiological analysis
Culture-positive cases, n (%)	19 (52.8%)
Fungal species distribution (n)
Alternaria alternata	9
Mycelia Sterilia	6
Fusarium spp.	2
Dematiaceous fungi	2

Detection rates and comparative analysis between UBM and slit-lamp examination

Slit-lamp examination revealed conjunctival chemosis in 12 patients (12 eyes), often with a spot suggestive of a foreign body shadow (Fig. 1a), while UBM further confirmed the presence of subconjunctival foreign bodies(Fig. 1b). UBM (35 MHz) initially detected chestnut-burr spines in 34 out of 36 eyes (94.4% detection rate). Two cases were missed on initial UBM: one with a spine located posteriorly in the pars plana region, and another where two closely adjacent spines could not be fully resolved.Statistical comparison of the detection rates between slit-lamp examination and UBM was performed using McNemar’s test. The results demonstrated a statistically significant superiority of UBM in identifying chestnut-burr spines (94.4% vs. 33.3%; P < 0.001).

Fig. 1.

Imaging of patients with slit‑lamp–occult versus slit‑lamp–visible foreign bodies. (a) Slit‑lamp microscopy shows a brown shadow suggestive of a foreign body (yellow arrow). (b) UBM reveals a hyperechoic foreign body within the conjunctiva, accompanied by conjunctival edema (yellow arrow). (c) Slit‑lamp photograph demonstrates marked conjunctival congestion; the foreign body is not visible. (d) UBM shows a hyperechoic foreign body within the sclera, associated with conjunctival edema (yellow arrow). (e) UBM measurement indicates a foreign body diameter of 310 μm.

Of the 34 eyes in which foreign bodies were identified by UBM, only 12 (35.3%) exhibited a subtle brownish shadow suggestive of a foreign body under slit-lamp biomicroscopy. In the remaining 22 eyes (64.7%), no foreign body could be visualized even with high-magnification slit-lamp photography or intraoperative microscopy. All of these “UBM-only” spines were located within the sclera. Compared with the slit-lamp-visible group (which included all 3 conjunctival and 9 superficial scleral spines), the occult spines showed the following features: (i)thicker and more edematous overlying conjunctiva (mean thickness: 1298 ± 446.8 μm vs. 554.2 ± 145.6 μm; P < 0.001; Fig. 1c); (ii)significantly greater mean implantation depth from the conjunctival surface (1466 ± 934.8 μm vs. 522.5 ± 142.5 μm; P < 0.001; Fig. 1d); and (iii) smaller residual spine diameter, predominantly below 500 μm (Fig. 1e). Comparative data are summarized in Table 2.

Table 2.

Characteristics of slit-lamp visible vs. occult foreign bodies.

Feature	Slit-lamp visible group (n = 12)	Slit-lamp occult group (n = 22)	P-value
Foreign body location	Conjunctiva: 3 Superficial sclera: 9	Deep sclera: 22
Depth from conjunctival surface (µm)	522.5 ± 142.5	1466 ± 934.8	< 0.001
Corresponding conjunctival thickness (µm)	554.2 ± 145.6	1298 ± 446.8	< 0.001

Foreign-body characteristics

Foreign bodies were categorized as conjunctival (Fig. 2a), scleral (Fig. 2b), or multiple (i.e., observed at different locations in the same patient; Fig. 2c,d). The distribution was conjunctival in 3 eyes (8.3%) and scleral in 33 eyes (91.7%). Notably, in a subset of patients, the spines were deeply embedded within the sclera, accompanied by severe conjunctival and scleral edema (Fig. 2e), with some even extending to involve the ciliary body (Fig. 2f). A single spine was present in 23 eyes (63.9%), while 13 eyes (36.1%) contained multiple spines (range: 2–4 per eye). No eye had more than five spines (Table 1).

Fig. 2.

UBM findings of Chestnut-burr spines at different ocular sites. (a) Conjunctival foreign body (yellow arrow) showing a punctate hyperechoic focus with acoustic shadow within the conjunctiva, accompanied by conjunctival edema. (b) Scleral foreign body (yellow arrow) presenting as a superficial punctate hyperechoic lesion with acoustic shadow in the sclera, associated with conjunctival edema and ciliary body edema. (c,d) Multiple hyperechoic foreign bodies (yellow arrows) detected as punctate hyperechoic foci at different sites within the same eye on UBM. (e) Deep intrascleral foreign body (yellow arrow) appearing as a punctate hyperechoic focus with acoustic shadow in the deep sclera, accompanied by conjunctival and ciliary body edema. (f) Foreign body involving the ciliary body region (yellow arrow), with associated conjunctival and ciliary body edema.

Time to presentation: abscess vs. uncomplicated scleritis

The interval from injury to initial presentation ranged from 1 to 70 days (mean 21.6 ± 16.4 days). Patients who developed scleral abscesses had a significantly longer presentation delay compared to those with uncomplicated scleritis (46.5 ± 21.4 days vs. 18.5 ± 13.1 days, respectively; independent samples t-test, t(34) = 3.84, P = 0.0005).

Microbiological findings

Fungal cultures were positive in 19 of 36 cases (52.8%) (Table 1). The identified species included Alternaria alternata (9 cases), Mycelia sterilia (6 cases), Fusarium spp. (2 cases), and dematiaceous fungi (2 cases). Histopathological examination of scleral abscess tissue confirmed the presence of fungal hyphae (Fig. 3a,b).

Fig. 3.

Histopathological examination demonstrates fungal hyphae (yellow arrow). (a) Calcofluor white staining, ×400 magnification, bar=100μm. (b) PAS staining, ×400 magnification, bar=100μm.

Scleral inflammation

General characteristics of scleral inflammation

All cases presented with scleritis and scleral thickening. As summarized in Table 3, scleral thickness demonstrated dynamic changes over time following foreign body removal. A one-way repeated-measures ANOVA revealed a statistically significant difference in scleral thickness across the time points (F(3, 105) = 15.82, P < 0.001). Post-hoc analysis showed that the scleral thickness at one week postoperatively (849.1 ± 256.5 μm) was not significantly different from the preoperative baseline (789.7 ± 200.8 μm, P > 0.05). The thickness peaked at one month post-surgery (965.7 ± 385.2 μm), which was significantly greater than the preoperative baseline (P < 0.001). By three months postoperatively, the thickness decreased to 570.4 ± 119.3 μm, being significantly thinner than the peak value at one month (P < 0.001) and showing no significant difference from the preoperative baseline level (P = 0.125).

Table 3.

UBM parameters of scleral thickness in chestnut-burr-related injury.

Time point	Scleral thickness (µm) (mean ± SD)	P-value (vs. baseline)	P-value (vs. 1-month peak)	Clinical significance
Baseline (pre-op)	789.7 ± 200.8	--	< 0.001	Inflammatory thickening
1 Week post-op	849.1 ± 256.5	0.751	0.342	Edema phase
1 Month post-op	965.7 ± 385.2	< 0.001	--	Peak edema phase
3 Months post-op	570.4 ± 119.3	0.125	< 0.001	Resolution of inflammatory thickening

Inflammatory progression in abscess cases

Four severe cases presented with scleral abscess, with a mean scleral thickness of 1225.0 ± 206.16 μm. In the representative case, slit‑lamp examination at initial presentation revealed marked conjunctival hyperemia and edema, with no visible foreign body (Fig. 4a). UBM at the same stage demonstrated hyperechoic foci within the sclera suggestive of a foreign body (Fig. 4b). Following removal of the chestnut thorn, conjunctival hyperemia and edema persisted, accompanied by marked congestion of scleral vessels (Fig. 4c). Moreover, UBM revealed full‑thickness scleral inflammation in severe cases, characterized by diffuse hypoechoic areas with tissue discontinuity in the abscess region, ciliary body edema, and elevated conjunctival echo (Fig. 4d). After intensive antifungal therapy combined with scleral repair surgery, conjunctival edema and scleral inflammation showed obvious improvement (Fig. 4e). At three months, three cases achieved significant clinical resolution, manifested by abscess subsidence and irregular but markedly improved scleral echogenicity (Fig. 4f).

Fig. 4.

Slit-lamp anterior segment photography and UBM imaging of the therapeutic course in a patient with suppurative scleritis. (a) Slit-lamp photograph showing marked conjunctival hyperemia and edema at initial presentation, with no imaging evidence of a chestnut thorn foreign body. (b) UBM image reveals significant conjunctival thickening and edema, with punctate hyperechoic foci accompanied by acoustic shadowing (yellow arrow) within the sclera. (c) Following removal of the chestnut thorn, conjunctival hyperemia and edema persist, along with marked congestion of scleral vessels. (d) Diffuse scleral hypoechogenicity with tissue discontinuity is observed in the abscess area (yellow arrow). (e) After scleral repair surgery, conjunctival edema and scleral inflammation show improvement. (f) Following abscess resolution, scleral echogenicity appears irregular but significantly improved (yellow arrow).

Management and outcomes of a refractory abscess

One refractory case exhibited localized white scleral elevation on slit-lamp examination (Fig. 5a) and a persistent scleral abscess with marked hypoechogenicity on UBM (Fig. 5b). Fungal hyphae were identified on histopathology. The condition eventually resolved after 6 months of therapy. In this severe abscess case, subsequent slit-lamp examination revealed a deepened scleral hue with visible underlying choroidal pigmentation (Fig. 5c), accompanied by severe scleral thinning to approximately 300 μm on UBM (Fig. 5d).

Fig. 5.

UBM and anterior segment imaging of the therapeutic course in a severe case of scleral abscess. (a) Slit-lamp photograph showing a localized white scleral elevation (yellow arrow). (b) UBM image reveals a scleral abscess with marked scleral thickening and reduced echogenicity (yellow arrow). (c) Slit-lamp view demonstrates deepened scleral hue with visible underlying choroidal pigmentation (yellow arrow). (d) UBM image shows severe scleral thinning (yellow arrow; thickness: approximately 300 μm).

Discussion

This study establishes UBM as an indispensable tool in the diagnosis and management of ocular injuries caused by chestnut-burr spines, effectively addressing two major clinical challenges: the acute phase of foreign body removal and the subacute phase of post-traumatic scleritis monitoring. While prompt surgical intervention is widely recommended to prevent severe sequelae^2,4,16, the minute size and occult nature of these spines have historically hampered precise localization, burden assessment, and depth determination, often leading to incomplete removal and iatrogenic injury.

Our findings demonstrate that UBM effectively overcomes these limitations. It achieved a remarkable preoperative detection rate of 94.4%, significantly surpassing the diagnostic yield of slit-lamp examination alone (33.3%), thereby confirming UBM’s established advantages in detecting radiographically occult foreign bodies¹⁷. By providing precise anatomic localization (conjunctival, scleral, or ciliary body), accurate fragment enumeration, and reliable depth assessment, UBM facilitates targeted surgical intervention. This was evidenced by the high rate of complete foreign body removal (91.7%) in a single procedure, markedly reducing the need for exploratory dissection and subsequent tissue trauma.

This high rate of complete removal is directly attributable to UBM’s superior detection capability. The analysis revealed that spines missed by slit-lamp were predominantly deep intrascleral, covered by significantly thickened and edematous conjunctiva, and of minute diameter (< 500 μm). This triad of deep location, overlying tissue reaction, and small size effectively renders them invisible to direct clinical examination. Importantly, in 64.7% (22/34) of UBM-positive eyes, the foreign bodies remained undetectable even upon meticulous slit-lamp re-examination and intraoperative microscopy, confirming that UBM identifies truly occult spines that would otherwise be missed.

Our findings provide further evidence supporting the selection of UBM as the first-line imaging modality for this specific injury. In our clinical setting, thin-slice CT and MRI were not prioritized as first-line tools for anterior segment evaluation due to their aforementioned limitations regarding the detection of minute, low-density, plant-based foreign bodies. UBM’s unique integration of ultra-high resolution, sufficient penetration (4–5 mm), sensitivity to low-density materials, and real-time bedside assessment proved critical.

This does not diminish the value of AS-OCT but rather clarifies a complementary diagnostic pathway. AS-OCT remains an excellent tool for detailed corneal and superficial conjunctival assessment, particularly in early or mild presentations without significant edema^9,10. However, our experience underscores that in cases of significant chemosis or when clinical suspicion remains high despite unremarkable AS-OCT findings, proceeding directly to UBM is a decisive step to exclude deep scleral or ciliary body involvement and to stage the inflammatory burden accurately.

Our longitudinal UBM monitoring revealed a key finding: inflammation and scleral thickening continued to progress paradoxically after surgery, peaking at one month even following successful chestnut-burr spines removal. This demonstrated that chestnut-burr spines extraction did not immediately terminate the inflammatory cascade, especially in cases with prolonged chestnut-burr spines retention or associated fungal inoculation. UBM served as a valuable objective tool for monitoring these cases¹⁸, providing quantitative metrics of inflammation (thickness, echogenicity) and assisting in guiding clinical and surgical management until resolution was achieved.

A critical observation was the strong association between delayed intervention and complication risk. Patients who developed scleral abscesses had a significantly longer interval from injury to initial treatment compared to those with uncomplicated scleritis. This finding underscores the urgency of timely diagnosis and surgical removal to mitigate the risk of severe complications. The strong association between delayed intervention and complications not only underscores the need for timely diagnosis but also highlights the importance of close postoperative monitoring, for which UBM proved invaluable.

The high prevalence of fungal infections (52.8%, 19/36) in our cohort, primarily comprising Alternaria alternata (9 cases) and Mycelia sterilia (6 cases), demonstrates the substantial microbiological complexity inherent in chestnut-burr-related ocular injuries^19,20. This finding is further reinforced by the consistent isolation of fungi from all severe abscess cases, providing compelling clinical evidence that fungal colonization significantly exacerbates scleral inflammatory progression. These observations collectively underscore the pivotal role of mycological factors in determining disease severity, suggesting that targeted antifungal therapy should be considered integral to the management of these complex cases.

Study limitations

This study has several limitations. Its single-center, retrospective design may introduce selection bias. The sample size, though substantial for this specific injury, was insufficient to robustly correlate specific fungal species with distinct scleral thickness trajectories. Furthermore, the diagnostic sensitivity for fungal infection is limited by traditional culture methods; future studies employing advanced molecular techniques like PCR could provide deeper microbiological insights. Finally, UBM findings are operator-dependent, though this was mitigated by having all images analyzed by a single experienced clinician. This study lacked a direct comparison cohort imaged with AS-OCT. Such comparisons would help further delineate the unique UBM findings specific to chestnut-burr injuries and more precisely quantify its added diagnostic value over other anterior segment imaging modalities.Future prospective studies incorporating such metrics would be valuable.

Conclusion

In conclusion, UBM is recommended as a first-line diagnostic and monitoring tool for chestnut-burr injuries. It maximizes the rate of complete primary foreign body removal, reducing the need for reoperation. Furthermore, its ability to quantify postoperative scleral inflammation provides a valuable objective guide for management, preventing underestimation of persistent infection or inflammation. Surgeons must be aware of potential scanning blind spots (e.g., far posterior pars plana) and exercise meticulous technique to avoid missing closely adjacent or deeply buried spines. Ultimately, while UBM-guided surgery and monitoring are crucial, primary prevention through protective eyewear during harvest remains the most effective strategy against these debilitating injuries²¹.

Author contributions

Data acquisition: M.Z., X.S., J.W., Q.K., Y.S., D.L. Writing (original draft): M.Z. Writing (review and editing): D.L. Final approval of manuscript: all authors.

Funding

This study was supported by the Qingdao Municipal Medical and Health Research Project (Grant No. 2025-WJKY190)

Data availability

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Declarations

Competing interests

The authors declare no competing interests.