Longitudinal Changes in Peripapillary Retinal Nerve Fiber Layer Thickness in Patients with Retinitis Pigmentosa

Abstract

Purpose

To perform a longitudinal analysis of peripapillary retinal nerve fiber layer (pRNFL) thickness in retinitis pigmentosa (RP) patients.

Design

A retrospective, longitudinal study.

Subjects

We enrolled patients diagnosed with RP and normal controls.

Methods

After the baseline visit, 3 additional measurements of pRNFL thickness at 1-year intervals were analyzed.

Main Outcome Measures

Peripapillary retinal nerve fiber layer thickness.

Results

In total, 142 eyes were included in the study: 72 in the RP group and 70 in the control group. Global pRNFL thicknesses were 89.3 ± 38.9, 86.5 ± 35.2, 84.6 ± 31.8, and 81.6 ± 31.3 μm at baseline, 1 year, 2 years, and 3 years in the RP group (P = 0.022), and 100.9 ± 6.3, 100.8 ± 7.0, 100.0 ± 6.3, and 100.3 ± 6.9 μm in the control group ( = 0.079), respectively. The reduction rate of pRNFL thickness was –2.45 μm/y in the RP group and –0.25 μm/y in the control group. In multivariate analysis, age (estimate = –0.55, P = 0.021) and RP stage (estimate = –15.42, P = 0.005) were significant factors associated with changes in pRNFL thickness in RP patients.

Conclusions

Retinitis pigmentosa patients exhibited a thinner pRNFL and a faster rate of thinning over time compared with healthy controls. In RP patients, pRNFL thinning was significantly associated with age and disease stage, possibly reflecting accelerated damage with disease progression.

Financial Disclosure(s)

The authors have no proprietary or commercial interest in any materials discussed in this article.

Retinitis pigmentosa (RP) is the most prevalent and severe inherited retinal disorder, ultimately leading to blindness. It has an estimated incidence of approximately 1 in 4000 individuals. It may present with diverse visual symptoms, such as night blindness and peripheral visual field loss, and often progresses to severe visual impairment; however, the onset, rate, and extent of progression can vary considerably among individuals.¹ Typical fundoscopic findings include peripheral pigmented bone spicule-like lesions, retinal arteriolar attenuation, and optic disc pallor.² These retinal changes result from mutations in genes that play crucial roles in the photoreceptors and retinal pigment epithelium.³ Therefore, early retinal changes in RP originate in the outer retina, which can be identified as outer retinal atrophy using OCT.

However, RP affects not only the outer retina but also the inner retinal layer thickness. Yoon et al⁴ reported that the ganglion cell-inner plexiform layer thickness decreased at the moderate and advanced stages of RP, and the retinal nerve fiber layer (RNFL) thickness of the macular area decreased at the advanced stage. Yıldırım et al⁵ reported that although the thinning of peripapillary RNFL (pRNFL) was predominantly observed in the inferior quadrant, the thickening was mostly noted in the temporal quadrant. Evaluating the inner retinal layers in RP patients is crucial, as it helps estimate the remaining retinal function and serves as a key indicator for future treatment strategies.6, 7, 8 However, to more accurately evaluate pRNFL thickness in RP patients, longitudinal analysis is necessary; nonetheless, such studies have been rarely conducted.

The aim of this study was to perform a longitudinal analysis of pRNFL thickness in patients with RP and to compare the findings with those of a healthy control group.

Methods

Patients

This study was conducted as a retrospective, longitudinal, and observational analysis in accordance with the principles of the Declaration of Helsinki. The study protocol received approval from the Institutional Review Board/Ethics Committee of Konyang University Hospital, Daejeon, Republic of Korea (No. 2025-03-022). Patients who attended the retinal clinic between March 2015 and December 2024 were evaluated for inclusion. Given the retrospective nature of the study, the Institutional Review Board/Ethics Committee of Konyang University Hospital granted a waiver for informed consent. Patients who were diagnosed with RP and followed up for >3 years were included. In our study, RP was diagnosed based on a combination of clinical history, functional testing, and characteristic fundus findings. Specifically, inclusion criteria for RP were as follows: (1) a history of night blindness; (2) peripheral visual field constriction presenting as concentric, ring-shaped, or island-type scotomas; (3) markedly reduced or nonrecordable rod and cone responses on full-field electroretinography; and (4) characteristic fundus changes, including bone spicule pigmentation, attenuation of retinal vessels, and optic disc pallor. All diagnoses were made by experienced retinal specialists based on comprehensive clinical evaluation. Patients with a history of intraocular surgery other than previous cataract surgery, those with any systemic diseases including diabetes and hypertension, and those with ophthalmic diseases other than RP, such as glaucoma, high myopia, epiretinal membrane, retinal vascular disease, macular disease, or optic disc disorders, were excluded. We also excluded patients showing cystoid macular edema, intraocular pressure >21 mmHg, and any kinds of retinal abnormalities during the follow-up period. The control group included patients without any systemic diseases, including diabetes or hypertension, who were diagnosed with a unilateral epiretinal membrane, macular hole, retinal detachment, or intraocular lens dislocation. Only fellow eyes without any ophthalmic disease were included in the analysis. After the initial visit, 3 additional examinations at 1-year intervals were analyzed. Patients with RP were classified into early, moderate, and advanced stages based on initial OCT findings, following criteria used in previous studies.⁴ The classification of moderate and advanced stages was determined by the presence or absence of the inner segment ellipsoid (ISE) zone within 2500 μm of the fovea in OCT images. In the moderate stage, the ISE zone was visible but limited to within 2500 μm of the fovea, whereas in the advanced stage, the ISE zone was absent. In contrast, the early stage was defined as a preserved ISE zone extending beyond 2500 μm from the fovea (Fig 1). If both eyes met the inclusion criteria in 1 person, the eye with the better OCT image quality was selected.

Figure 1.

Representative OCT images of each stage. A, Early stage showing preserved ISE zone. B, Moderate stage with visible ISE within 2500 μm from the fovea. C, Advanced stage with invisible ISE. ISE = inner segment ellipsoid.

pRNFL Thickness Measurements

A trained examiner assessed pRNFL thickness using spectral-domain OCT (Spectralis; Heidelberg Engineering). The scans were performed in a circular pattern with a 3.5 mm diameter centered on the optic nerve head, measuring pRNFL thickness in both global and sectoral regions, including the temporal, superotemporal, superonasal, nasal, inferonasal, and inferotemporal sectors. Two independent observers (J.-T.K. and M.-W.L.) reviewed the OCT images, and scans with a quality score below 15, as well as those exhibiting decentration, misalignment, or significant segmentation errors, were excluded from the analysis.

Statistical Analysis

Independent t tests were used to compare baseline demographic characteristics and ocular parameters between groups, whereas categorical variables were analyzed using chi-squared tests. The Kruskal–Wallis test was used to compare the baseline global pRNFL thickness among the disease stages within the RP group. To evaluate changes in pRNFL thickness over time within each group, including the rate of thinning, linear mixed models with a random intercept at the eye level were applied. Additionally, generalized linear mixed models were employed to identify factors influencing pRNFL thickness changes over time in the RP group, with best-corrected visual acuity, intraocular pressure, and time entered as values measured at each visit, and all other factors entered as baseline values. All statistical analyses were conducted using SPSS software (version 18.0; IBM Corp).

Results

Demographic Characteristics

In the initial screening, 109 cases were diagnosed with RP and had follow-up data spanning more than 3 years at annual intervals. Among them, 7 cases with concomitant epiretinal membrane, 5 with macular edema, 4 with choroidal neovascularization, 13 with glaucoma, and 8 with segmentation errors on OCT images were excluded. Consequently, a total of 72 cases were included in the RP group and 70 cases in the control group (Table 1). The mean age was 47.9 ± 16.1 years in the RP group and 51.7 ± 14.9 years in the control group (P = 0.215). Other characteristics, including sex, spherical equivalent, and intraocular pressure, were not statistically different between the 2 groups. The mean best-corrected visual acuity was 0.32 ± 0.29 in the RP group and 0.01 ± 0.02 in the control group (P < 0.001), and central macular thickness was 245.8 ± 50.7 and 276.1 ± 19.6 μm (P < 0.001), respectively. Although some patients experienced disease progression during the follow-up period, none showed sufficient change to be reclassified.

Table 1.

Baseline Demographics

	RP Group (n = 72)	Control Group (n = 70)	P Value
Age (yrs, mean ± SD)	47.9 ± 16.1	51.7 ± 6.6	0.215
Sex (n, %)	33 (45.8)	38 (54.3)	0.807
SE (diopters, mean ± SD)	–1.39 ± 2.19	–0.85 ± 2.16	0.261
IOP (mmHg, mean ± SD)	13.5 ± 3.4	13.7 ± 2.6	0.785
BCVA (logMAR, mean ± SD)	0.32 ± 0.29	0.01 ± 0.02	<0.001
CMT (μm, mean ± SD)	245.8 ± 50.7	276.1 ± 19.6	0.002

BCVA = best-corrected visual acuity; IOP = intraocular pressure; CMT = central macular thickness; logMAR = logarithm of the minimum angle of resolution; RP = retinitis pigmentosa; SD = standard deviation; SE = spherical equivalent.

P values that are statistically significant (P < 0.050) are in bold font.

pRNFL Thickness at Each Visit

At baseline, the pRNFL thicknesses of the global area and the temporal, superotemporal, superonasal, nasal, inferonasal, and inferotemporal sectors were 89.3 ± 38.9, 91.7 ± 39.5, 132.0 ± 59.4, 90.4 ± 65.8, 47.4 ± 34.7, 75.0 ± 40.9, and 132.0 ± 55.5 μm in the RP group and 100.9 ± 6.3, 80.3 ± 13.7, 141.0 ± 11.8, 108.0 ± 18.0, 67.5 ± 12.4, 110.4 ± 14.8, and 150.9 ± 15.7 μm in the control group, respectively (Table 2). All sectors, except for the superotemporal region, showed a significant difference between the 2 groups. Unlike other sectors, the temporal sector was thicker in the RP group (Fig 2).

Table 2.

Peripapillary Retinal Nerve Fiber Layer Thickness at Baseline

	RP Group	Control Group	P Value
Global	89.3 ± 38.9	100.9 ± 6.3	0.016
Temporal	91.7 ± 39.5	80.3 ± 13.7	0.034
Superotemporal	132.0 ± 59.4	141.0 ± 11.8	0.221
Superonasal	90.4 ± 65.8	108.0 ± 18.0	0.039
Nasal	47.4 ± 34.7	67.5 ± 12.4	<0.001
Inferonasal	75.0 ± 40.9	110.4 ± 14.8	<0.001
Inferotemporal	132.0 ± 55.5	150.9 ± 15.7	0.009

RP = retinitis pigmentosa.

P values that are statistically significant (P = 0.050) are in bold font.

Figure 2.

Mean pRNFL thickness with bars showing 95% confidence intervals in each visit. ∗Statistically significant changes over time (P < 0.050). pRNFL = peripapillary retinal nerve fiber layer; RP = retinitis pigmentosa.

In the RP group, global pRNFL thicknesses were 89.3 ± 38.9, 86.5 ± 35.2, 84.6 ± 31.8, and 81.6 ± 31.3 μm at baseline, 1 year, 2 years, and 3 years, respectively (P = 0.022), which showed a significant reduction over time (Table 3) (Fig 3). In the control group, global pRNFL thicknesses were 100.9 ± 6.3, 100.8 ± 7.0, 100.0 ± 6.3, and 100.3 ± 6.9 μm at baseline, 1 year, 2 years, and 3 years, respectively (P = 0.079), indicating a lack of a significant change over time. Although there were no significant differences in pRNFL thicknesses between the 2 groups at baseline after Bonferroni correction (P = 0.016), the disparity increased over time, with significant differences observed at 1 (P = 0.001), 2 (P < 0.001), and 3 years (P < 0.001). In terms of sectoral pRNFL thickness, similar to the global measurements, the RP group exhibited a general trend of progressive thinning over time, whereas the control group remained stable throughout the follow-up period.

Table 3.

Global Peripapillary Retinal Nerve Fiber Layer Thickness at Each Visit

	RP Group	Control Group	P Value
Baseline	89.3 ± 38.9	100.9 ± 6.3	0.016
1 yr	86.5 ± 35.2	100.8 ± 7.0	0.001
2 yrs	84.6 ± 31.8	100.0 ± 6.3	<0.001
3 yrs	81.6 ± 31.3	100.3 ± 6.9	<0.001

P values that are statistically significant after Bonferroni correction (P < 0.013) are in bold font.

RP = retinitis pigmentosa.

Figure 3.

Scatterplots showing change from baseline in global peripapillary retinal nerve fiber layer thickness at 1, 2, and 3 years in patients with retinitis pigmentosa. For each eye, the change was calculated as baseline minus follow-up thickness at the corresponding time point, so positive values indicate thinning relative to baseline. Each line connects measurements from the same eye across time points.

In the RP group, the early, moderate, and advanced stages comprised 9, 42, and 21 eyes, with baseline pRNFL thicknesses of 99.5 ± 21.3, 94.4 ± 39.6, and 74.6 ± 35.7 μm, respectively (P = 0.011). Patients in the moderate (1 year, 92.5 ± 40.5 μm; 2 years, 89.6 ± 35.9 μm; 3 years, 85.5 ± 34.7 μm; P = 0.005) and advanced (1 year, 68.7 ± 19.3 μm; 2 years, 68.4 ± 20.4 μm; 3 years, 65.9 ± 20.3 μm; P = 0.020) stages showed a significant decrease in pRNFL thickness over time, whereas those in the early stage (1 year, 100.3 ± 21.2 μm; 2 years, 99.1 ± 17.2 μm; 3 years, 99.7 ± 19.8 μm; P = 0.915) did not.

Rate of pRNFL Thinning and Factors Associated with Changes in pRNFL Thickness in the RP Group

The reduction rate of global thickness in the RP group was –2.45 μm/y (Table 4). A decreasing trend was observed in all sectors, with the superotemporal, superonasal, and nasal sectors showing significant rates of reduction. In contrast, the control group showed no significant changes in either global or sectoral thicknesses over time.

Table 4.

Rates of Change in Peripapillary Retinal Nerve Fiber Layer Thickness

	RP Group	P Value	Control Group	P Value
General	–2.45 (–4.54 to –0.37)	0.022	–0.25 (–0.54 to 0.03)	0.079
Temporal	–1.90 (–3.82 to 0.02)	0.052	–0.07 (–0.63 to 0.48)	0.791
Superotemporal	–2.98 (–5.85 to –0.11)	0.042	–0.57 (–1.58 to 0.43)	0.259
Superonasal	–5.17 (–7.93 to –2.42)	<0.001	–0.69 (–2.03 to 0.65)	0.304
Nasal	–2.58 (–4.65 to –0.50)	0.015	0.16 (–0.75 to 1.01)	0.727
Inferonasal	–3.43 (–6.91 to 0.05)	0.054	–0.59 (–1.73 to 0.54)	0.302
Inferotemporal	–1.30 (–4.76 to 2.15)	0.458	–0.35 (–1.15 to 0.45)	0.380

P values that are statistically significant (P < 0.050) are in bold font.

RP = retinitis pigmentosa.

In univariate analysis, age (estimate = –0.67, P = 0.002), RP stage (estimate = –17.67, P = 0.002), lens status (phakic or pseudophakic; estimate = 17.94, P = 0.033), and time (estimate = –2.45, P = 0.022) were significant factors associated with pRNFL thickness in the RP group (Table 5). In multivariate analysis, age (estimate = –0.55, P = 0.021), stage (estimate = –15.42, P = 0.005), and time (estimate = –2.46, P = 0.021) remained significant.

Table 5.

Linear Mixed-Effect Model Determination of Factors Associated with Changes in Peripapillary Retinal Nerve Fiber Layer Thickness in RP Group

	Univariate		Multivariate
	Estimate (95% CI)	P Value	Estimate (95% CI)	P Value
Age	–0.67 (–1.09 to –0.24)	0.002	–0.55 (–1.02 to –0.09)	0.021
Sex	–9.01 (–23.36 to 5.34)	0.215
RP stage	–17.67 (–28.47 to –6.87)	0.002	–15.42 (–26.03 to –4.80)	0.005
Lens	17.94 (1.46 to 34.41)	0.033	2.65 (–15.21 to 20.50)	0.768
BCVA	–2.96 (–18.10 to 12.18)	0.700
SE	1.43 (–1.88 to 4.74)	0.393
IOP	0.92 (–1.19 to 3.02)	0.387
CMT	0.07 (–0.01 to 0.15)	0.082
Time	–2.45 (–4.54 to –0.37)	0.022	–2.46 (–4.54 to –0.38)	0.021

BCVA = best-corrected visual acuity; CI = confidence interval; CMT = central macular thickness; IOP = intraocular pressure; RP = retinitis pigmentosa; SE = spherical equivalent.

P values that are statistically significant (P < 0.050) are in bold font.

Discussion

Although RP primarily affects the photoreceptors and retinal pigment epithelium, growing evidence suggests that inner retinal structures also undergo progressive changes. Given that many of the current and upcoming therapeutic modalities (e.g., gene therapy, neurotrophic factor delivery, retinal prostheses, and stem cell–based therapies) rely on the preservation of inner retinal integrity, reliable and quantifiable biomarkers of inner retinal status are of critical importance. In this context, pRNFL thickness could represent a more layer-specific structural parameter than global retinal thickness, which encompasses multiple retinal layers and may be less sensitive to subtle or localized changes. In addition, compared with the measurement of inner retinal thickness in the macular area, which can be affected by concomitant epiretinal membrane or macular edema in RP, pRNFL thickness is far less influenced by such conditions. Therefore, pRNFL thinning could potentially serve as a structural biomarker for disease progression or treatment response in clinical trials. Moreover, assessing pRNFL integrity could assist in identifying suitable candidates for interventions that depend on viable inner retinal neurons for visual signal transmission.

In light of these considerations, we sought to investigate longitudinal changes in pRNFL thickness in RP using a robust study design and modern imaging technology, thereby overcoming the limitations of previous research. Although a previous longitudinal study on pRNFL thickness in patients with RP has been reported, it had several limitations, such as the absence of a control group, the use of Stratus OCT (which may have lower measurement accuracy compared with current devices), and the inclusion of only two time points with varying intervals between them for each patient.⁹ In our study, we conducted a longitudinal analysis comparing the pRNFL thickness between patients with RP and healthy individuals over a period of 3 years at 1-year intervals. At baseline, the global pRNFL thickness tended to be thinner in the RP group than in the control group. Over time, the RP group showed more rapid thinning, leading to significantly lower values at the first, second, and third years. These longitudinal changes in pRNFL thickness were significantly associated with both age and RP stage as assessed via OCT.

At baseline, the global pRNFL thickness was thinner in the RP group compared with the control group, and this difference became more pronounced over time. Additionally, the RP group showed a significant decrease in global pRNFL thickness over time, whereas the control group did not. The reduction rate of pRNFL thickness was –2.45 μm/y in the RP group and –0.25 μm/y in the control group, whereas a previous study reported that the mean rate of decrease of RP patients was calculated as –1.63 ± 2.0 μm/y (range, –8.3 to +3.4 μm/y).⁹ Because of differences in the OCT devices between our study and that previous one, direct comparison is limited; however, the notably thicker baseline pRNFL in their study (105.8 ± 22.7 μm), compared with ours (89.3 ± 38.9 μm), suggests that our study may have included more advanced RP cases, potentially accounting for the greater thinning rate observed. The rate of pRNFL thinning observed in this study is substantially greater than that reported in association with systemic conditions such as hypertension or diabetes, or with high myopia, all of which influence pRNFL thickness.10, 11, 12 This fast reduction of pRNFL may be associated with transneuronal anterograde degeneration caused by decreased neuronal input from the photoreceptors and vascular insufficiency.^13,14 In addition to RP, inner retinal alterations have also been reported in other inherited photoreceptor diseases, such as Stargardt disease. Previous studies using OCT have demonstrated sectoral thinning of the pRNFL in patients with Stargardt disease.^15,16 Although the underlying pathophysiology differs from that of RP, these findings support the broader concept that inner retinal remodeling may occur across various photoreceptor degenerations. This underscores the importance of assessing inner retinal integrity when evaluating disease progression and considering therapeutic interventions in inherited retinal disorders.

Similar to other diseases that affect pRNFL thickness, previous studies have reported that the pRNFL thickness in the inferior sector was notably thinner in patients with RP.^5,17 Our study also showed a significantly thinner pRNFL in inferior sectors than that of normal controls at baseline. Although the rate of pRNFL thinning in the inferior sectors was not statistically significant, this may be attributable to the higher proportion of patients with moderate- to advanced-stage RP compared to those with early-stage disease. It is possible that the inferior sectors in these patients had already undergone rapid RNFL thinning in earlier stages and had reached a plateau by the time of evaluation. The larger difference in RNFL thickness between the RP group and the control group in the inferior sectors compared with the superior sectors at baseline suggests this possibility. This may be due to the increased metabolic demand caused by anatomical structures, such as larger laminar pores and less connective tissue support, making the RNFL in the inferior sector more susceptible to various types of damage.^18,19

Previous studies have reported that the pRNFL thickness in the temporal sector is increased in patients with RP.^5,17 In this study, the temporal pRNFL thickness in RP patients was significantly thicker than in the control group at baseline, which is consistent with previous studies. Although it showed a tendency to decrease over time, it remained thicker than the control group even at the 3-year point. The exact mechanism behind the thickening of temporal pRNFL thickness is unclear; however, it may be the result of glial tissue proliferation secondary to RNFL atrophy, which is most prominently observed between the temporal arcades.^5,20 Further pathological and anatomical studies are needed to confirm this. Additionally, because the temporal pRNFL was thicker than the control group at baseline but showed a decreasing trend over time, it can be inferred that the temporal pRNFL thickening occurs in the very early stages of RP. Evaluating patients with very early-stage RP to confirm the thickening of temporal pRNFL would also be meaningful research.

Previous studies have reported a significant association between pRNFL thickness and age in patients with RP. Anastasakis et al¹⁷ reported that a significant negative correlation between age and overall pRNFL thickness in patients with RP has been demonstrated through linear regression analysis. Oishi et al⁹ also reported a negative correlation between the average pRNFL thickness and age in their cross-sectional multivariate linear regression analysis. Our study showed that a change in pRNFL thickness of RP patients was significantly associated with age, which was consistent with previous studies. In healthy individuals, pRNFL is known to gradually thin over time, and a similar slight thinning trend was observed in the control group of this study.^21,22 The onset of disease may vary depending on the type of RP; however, once the disease begins, it progresses gradually over time. As a result, the influence of age on pRNFL thickness is expected to be significantly greater in patients with RP than in healthy individuals.

Change in pRNFL thickness was significantly associated with RP stages based on the OCT status. Although the number of enrolled early-stage patients was relatively small, warranting further studies with larger samples, our study found no significant decrease in pRNFL thickness over time in this group. This may be because a more extensive and substantial level of outer retinal damage, as seen in moderate or more advanced stages, is required for the acceleration of pRNFL thinning. To confirm this, further studies including a larger number of patients in each stage are needed. Meanwhile, Yoon et al⁴ reported that a decrease in ganglion cell-inner plexiform layer thickness was observed starting from the moderate stage, while a reduction in macular RNFL thickness was seen starting from the advanced stage in RP patients. This may be because the RNFL in the peripapillary area is thicker than that in the macular area, making changes more pronounced. Consequently, the peripapillary region may serve as a more sensitive indicator of RNFL damage in RP.

This study had several limitations. First, its retrospective design inevitably introduced selection bias. Second, as genotyping information was not available, we could not stratify patients by inheritance pattern. Although family history suggested a small number of autosomal dominant, autosomal recessive, and X-linked cases, the sample size was too limited and uncertain to allow meaningful analysis. In particular, X-linked RP associated with RP2 or RPGR mutations may show more rapid progression, but this could not be further evaluated in the present study. In our analysis, the standard deviation of the data was larger even within each disease stage compared with the control group, which may be attributable to the inclusion of patients with various genotypes. Further studies that include genotyping on a larger number of patients are needed. Third, the classification method used for RP disease staging in this study was based on a previous report; however, this approach is not yet widely adopted. Therefore, caution is warranted when generalizing our results across studies using different staging criteria.

In conclusion, the pRNFL was thinner in RP patients, and the rate of decrease over time was also faster compared with healthy individuals. In most sectors, the trend was similar to that of the global area; however, in the temporal sector, RP patients tended to have a thicker pRNFL. This pRNFL thickness change in RP patients was significantly associated with age and RP stage based on the OCT, which may reflect the acceleration of pRNFL damage as the disease progresses over time. These findings may be valuable for evaluating comorbidities that could influence pRNFL thickness in RP patients, contributing to a deeper understanding of the mechanisms underlying changes in retinal structure in RP and informing future research on treatments for retinal neurodegeneration.

Data Availability

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

Manuscript no. XOPS-D-25-00357.