Retrobulbar microvascular and biomechanical changes associated with axial elongation in myopic eyes

Abstract

This study aimed to investigate retrobulbar biomechanical and microvascular changes associated with increasing axial length in myopic eyes using shear wave elastography and a quantitative vascularity index. In this prospective cross-sectional study, 99 eyes from 99 adults were classified into three groups according to axial length: <24.00 mm (Group 1), 24.00–25.99 mm (Group 2), and ≥ 26.00 mm (Group 3). All participants underwent comprehensive ophthalmologic and ultrasonographic evaluations. Shear wave elastography was used to quantify the stiffness of the optic nerve and adjacent retrobulbar fat tissue. Retrobulbar microvascularity was assessed using ultra-microangiography, with color pixel percentage measured as a vascularity index. No significant differences in tissue stiffness were observed among axial length groups (all p > 0.05). However, the vascularity index differed significantly between groups (p = 0.026) and remained independently associated with axial length after adjusting for age and sex (p = 0.041), suggesting progressive reduction in retrobulbar microvascularity, reflected by lower vascularity index values, with increasing axial elongation. Optic nerve diameter significantly decreased with increasing axial length (p = 0.010). These findings indicate that axial elongation in myopic eyes is associated with significant retrobulbar microvascular changes without corresponding alterations in tissue stiffness.

Introduction

Myopia represents a significant global public health challenge, with high myopia distinguished by excessive axial elongation¹. This progressive increase in axial length (AL) induces complex structural and biomechanical changes within the posterior segment of the eye, extending beyond the globe itself².

The effects of myopia on retinal and choroidal vasculature have been extensively documented by numerous studies^3,4. However, associated changes within the retrobulbar compartment related to continuing axial elongation are less known. Despite the anatomical and biomechanical continuity between the globe and the tissues posterior to it, potential vascular changes beyond the sclera have received relatively limited attention.

Elastography uses ultrasound imaging to distinguish tissues based on differences in mechanical elasticity⁵. Shear-wave elastography (SWE) allows quantitative assessment of the elasticity of soft tissues using contemporary ultrasonography systems⁶. Shear waves travel through tissues in a transverse manner, producing tangential motion between tissue layers at relatively low velocities of 1–10 m/s. By comparison, pressure waves used in standard ultrasound imaging propagate through compressive tissue deformation at much higher speeds, on the order of 1500 m/s. In elastographic imaging, shear waves reflect the elastic behavior of tissues when subjected to low-frequency mechanical vibrations between 50 and 200 Hz⁵.

Although SWE has been increasingly utilized to quantitatively assess tissue stiffness in various ophthalmic and orbital conditions^7–10, existing studies predominantly focus on elasticity measurements of individual structures such as the optic nerve or surrounding retrobulbar tissues. However, tissue stiffness alone fails to capture the full spectrum of biomechanical and microvascular adaptations associated with axial elongation. Altered microvascular perfusion in the retrobulbar region may serve as an early marker of biomechanical or vascular changes related to AL that are beyond the scope of SWE⁴.

Accordingly, the present study uses a quantitative vascularity index alongside SWE to provide a more comprehensive assessment of retrobulbar tissue characteristics across increasing AL groups. This combined approach allows evaluation of both tissue mechanical properties and vascular dynamics, offering deeper insight into the pathophysiological effects of axial elongation on ocular and retrobulbar tissues. To the best of our knowledge, this study is the first to concurrently evaluate SWE and a quantitative vascularity index to assess retrobulbar tissue changes associated with axial elongation in myopic eyes.

Results

Demographic and clinical characteristics

The study cohort comprised a total of 99 eyes from 99 patients, with 33 eyes from 33 patients included in each group. There was no significant difference among the three groups with respect to sex distribution (p = 0.831). In contrast, significant differences were observed in age, best corrected visual acuity (BCVA), spherical equivalent (SE), and AL across the groups (p = 0.004, p < 0.001, p < 0.001, and p < 0.001, respectively) (Table 1).

Table 1.

Demographic and clinical characteristics of the study population.

Parameter	Entire Cohort	Group 1	Group 2	Group 3	p value
Number of patients/eyes, n	99/99	33/33	33/33	33/33	-
Age, years (mean ± SD) [min – max]	34.86 ± 13.86 [18–66]	37.45 ± 10.96 [19–62]	29.30 ± 12.80 [18–58]	39.58 ± 15.02 [18–66]	0.004 φac
Gender, n (%) Male Female	32 (32.3) 67 (67.7)	10 (30.3) 23 (69.7)	10 (30.3) 23 (69.7)	12 (36.4) 21 (63.6)	0.831γ
BCVA, logMAR (mean ± SD) [min – max]	0.23 ± 0.39 [0.00–1.30]	0.00 ± 0.00 [0.00–0.00]	0.05 ± 0.15 [0.00–0.70]	0.63 ± 0.44 [0.00–1.30]	< 0.001 φbc
SE, diopters (mean ± SD) [min – max]	−5.07 ± 5.31 [(−20.00) – (0.00)]	−0.66 ± 0.84 [(−3.50) – (0.00)]	−3.19 ± 2.05 [(−8.00) – (0.00)]	−11.35 ± 4.15 [(−20.00) – (−3.50)]	< 0.001 φabc
AL, mm (mean ± SD) [min – max]	25.31 ± 2.37 [22.00–31.15]	23.01 ± 0.57 [22.00–23.93]	24.77 ± 0.59 [24.00–25.89]	28.16 ± 1.56 [26.03–31.15]	< 0.001 φabc

AL, axial length; BCVA, best corrected visual acuity; SD, standard deviation; SE, spherical equivalent.

^φ Kruskal-Wallis test.

^γ Pearson chi-square test.

^a Post-hoc significant difference between Group 1 and Group 2.

^b Post-hoc significant difference between Group 1 and Group 3.

^c Post-hoc significant difference between Group 2 and Group 3.

Post-hoc analyses revealed that patients in Group 2 were significantly younger than those in Groups 1 and 3 (Mann-Whitney U test with Bonferroni correction; p = 0.022 and p = 0.008, respectively). Best corrected visual acuity and SE differed significantly across all pairwise group comparisons, with Group 3 exhibiting the poorest visual acuity and the highest myopic refractive error (all p < 0.05) (Table 1).

Intergroup comparisons of ultrasonographic parameters

Significant differences were observed among the groups in terms of optic nerve diameter (p = 0.002), with Group 3 exhibiting lower values compared with Group 1 and Group 2 (Mann-Whitney U test with Bonferroni correction; p = 0.003 and p = 0.020, respectively). The vascularity index also showed significant intergroup difference (p = 0.026), with Group 3 exhibiting lower values compared with Group 2 (one-way analysis of variance [ANOVA] with Bonferroni correction; p = 0.030). In contrast, no significant intergroup differences were identified with respect to SWE measurements of the optic nerve, retrobulbar fat tissue, or the SWE ratio (p = 0.987, p = 0.194, and p = 0.660, respectively) (Table 2). No adverse events or patient-reported discomfort were observed during or after the ultrasonographic examinations.

Table 2.

Comparison of the ultrasonographic measurements across the groups.

Parameter, mean ± SD [min – max]	Entire Cohort (n = 99)	Group 1 (n = 33)	Group 2 (n = 33)	Group 3 (n = 33)	p value
Optic nerve diameter, mm	3.05 ± 0.55 [1.90–5.10]	3.19 ± 0.53 [1.90–4.20]	3.11 ± 0.41 [2.40–3.90]	2.84 ± 0.64 [1.95–5.10]	0.002 φab
SWE - optic nerve, kPa	12.21 ± 4.54 [4.36–24.91]	12.22 ± 4.20 [4.99–24.91]	12.49 ± 5.23 [4.39–24.91]	11.93 ± 4.25 [4.36–20.53]	0.987φ
SWE - fat tissue, kPa	8.05 ± 3.69 [3.07–22.39]	8.21 ± 2.50 [4.07–15.84]	8.34 ± 4.44 [3.07–22.39]	7.60 ± 3.93 [3.08–20.68]	0.194φ
SWE - ratio	1.70 ± 0.76 [0.40–4.66]	1.63 ± 0.78 [0.69–4.49]	1.72 ± 0.79 [0.40–3.83]	1.74 ± 0.72 [0.90–4.66]	0.660φ
Vascularity index	34.28 ± 10.01 [11.90–58.38]	35.38 ± 8.98 [19.33–51.36]	36.90 ± 10.13 [23.76–58.38]	30.58 ± 10.08 [11.90–47.58]	0.026 λb

SD, standard deviation; SWE, shear wave elastography.

^φ Kruskal-Wallis test.

^λ One-way analysis of variance (ANOVA).

^a Post-hoc significant difference between Group 1 and Group 3.

^b Post-hoc significant difference between Group 2 and Group 3.

Correlation analysis

Correlation analysis between ultrasonographic measurements and clinical characteristics demonstrated that optic nerve diameter was moderately negatively correlated with BCVA (r = −0.393, p < 0.001) and AL (r = −0.346, p < 0.001), and moderately positively correlated with SE (r = 0.355, p < 0.001). Shear wave elastography measurements of the retrobulbar fat tissue exhibited a weak positive correlation with SE (r = 0.233, p = 0.020). The vascularity index showed a moderate negative correlation with age (r = −0.312, p = 0.002), a weak negative correlation with BCVA (r = −0.203, p = 0.044), and a weak positive correlation with SE (r = 0.203, p = 0.044). No significant correlations were identified between any other parameters (Table 3).

Table 3.

Spearman’s correlation analysis between ultrasonographic measurements and clinical characteristics.

	Age	BCVA	SE	AL
Optic nerve diameter, r (p)	−0.053 (0.604)	−0.393 (< 0.001)	0.355 (< 0.001)	−0.346 (< 0.001)
SWE - optic nerve, r (p)	0.125 (0.218)	0.031 (0.759)	0.070 (0.488)	0.009 (0.929)
SWE - fat tissue, r (p)	0.103 (0.308)	−0.151 (0.136)	0.233 (0.020)	−0.190 (0.060)
SWE - ratio r (p)	−0.020 (0.844)	0.120 (0.236)	−0.093 (0.359)	0.105 (0.303)
Vascularity index, r (p)	−0.312 (0.002)	−0.203 (0.044)	0.203 (0.044)	−0.162 (0.109)

AL, axial length; BCVA, best corrected visual acuity; r, correlation coefficient; SE, spherical equivalent; SWE, shear wave elastography.

Regression analysis

Given that age and sex may potentially influence ultrasonographic measurements, multivariate regression analyses were performed to assess the independent effect of AL on ultrasonographic parameters. After adjustment for age and sex, optic nerve diameter remained independently associated with AL, with longer AL predicting lower optic nerve diameter values (B = −0.066, p = 0.005). This model accounted for 6.1% of the variance in optic nerve diameter (adjusted R² = 0.061).

The vascularity index was independently associated with both age and AL. Increasing age (B = −0.183, p = 0.010) and longer AL (B = −0.713, p = 0.041) were associated with lower vascularity index values. This model explained 20.1% of the variance in vascularity index (adjusted R² = 0.201).

In contrast, SWE measurements of the optic nerve, retrobulbar fat tissue, and the SWE ratio were not independently associated with age, sex, or AL (all p > 0.05) (Table 4).

Table 4.

Multivariate linear regression analyses evaluating the association between axial length and ultrasonographic measurements.

Model	B	Standard Error	β	p value	95% CI
Optic nerve diameter*
Age	0.001	0.004	−0.006	0.955	−0.008 to 0.008
Gender	−0.158	0.119	−0.135	0.187	−0.393 to 0.078
AL	−0.066	0.023	−0.285	0.005	−0.112 to −0.020
SWE - optic nerve
Age	0.019	0.035	0.058	0.581	−0.050 to 0.088
Gender	−1.847	1.004	−0.191	0.069	−3.389 to 0.146
AL	−0.076	0.196	−0.04	0.699	−0.466 to 0.313
SWE - fat tissue
Age	0.012	0.029	0.044	0.68	−0.045 to 0.069
Gender	0.023	0.832	0.003	0.978	−1.628 to 1.674
AL	−0.124	0.163	−0.08	0.448	−0.447 to 0.199
SWE - ratio
Age	−0.001	0.006	−0.015	0.89	−0.012 to 0.011
Gender	−0.197	0.169	−0.122	0.247	−0.533 to 0.139
AL	0.026	0.033	0.081	0.435	−0.040 to 0.092
Vascularity index*
Age	−0.183	0.069	−0.249	0.01	−0.320 to −0.046
Gender	1.84	1.01	0.274	0.07	−0.160 to 3.850
AL	−0.713	0.389	−0.169	0.041	−1.485 to −0.060

AL, axial length; B, unstandardized coefficient; β, standardized coefficient; CI, confidence interval; SWE, shear wave elastography.

* Adjusted R² values are reported only for regression models demonstrating statistically significant associations: 0.061 for optic nerve diameter and 0.201 for vascularity index.

Discussion

In the present study, we categorized eyes according to AL to better evaluate structural changes associated with axial elongation, as refractive error does not always accurately reflect posterior segment anatomy. With this approach, we found that increased AL in myopic eyes was associated with significant retrobulbar microvascular alterations, while no corresponding changes in tissue stiffness were detected by SWE. These findings differ from previous in vivo elastography studies by Yuan et al.²and Qian et al.⁷, who reported reduced posterior scleral or eyewall elasticity with increasing AL, suggesting that biomechanical alterations related to axial elongation may be region-specific rather than uniformly distributed across retrobulbar tissues. Notably, the vascularity index remained independently associated with AL after adjustment for age and sex, while elastographic parameters of the optic nerve and adjacent retrobulbar fat tissue showed no significant relationship. Taken together, these results indicate that microvascular changes may accompany axial elongation before measurable biomechanical alterations become apparent in the retrobulbar compartment.

Ultra-microangiography (UMA) is an advanced ultrasound method that provides improved visualization of microvascular blood flow, particularly at low velocities, without requiring contrast agents¹¹. In the present study, UMA was used to derive a quantitative vascularity index based on color pixel percentage (CPP), providing an objective measure of retrobulbar microvascularity¹². Our findings demonstrate that retrobulbar vascularity decreases with increasing AL, indicating a close relationship between axial elongation and microvascular alterations. The combined use of SWE and UMA thus provides complementary biomechanical and microvascular information, allowing a more comprehensive evaluation of retrobulbar tissue changes associated with axial elongation.

Evaluating tissue elasticity and stiffness has been shown to contribute meaningfully to the differential diagnosis of a wide range of conditions¹³. Conventional ultrasonic waves primarily reflect tissue density and compressive behavior, whereas mechanical shear waves characterize tissue responses to shear stress, thereby offering complementary information on tissue elasticity¹⁴. The posterior segment of the eye is a biomechanically complex structure in which the optic nerve and surrounding peripapillary tissues play a central role in visual function. Biomechanical alterations in these tissues may impair axoplasmic transport at the optic nerve head, contributing to retinal ganglion cell loss and subsequent visual dysfunction⁹. Accordingly, in contrast to the multi-regional posterior segment elastography approach described by Qian et al.⁷, the present study prioritized a targeted and standardized measurement protocol. Shear wave elastography was performed at anatomically consistent retrobulbar locations, focusing on the optic nerve and adjacent fat tissue, to enhance reproducibility and minimize anatomical variability. The use of a SWE ratio provided an internally normalized estimate of tissue elasticity, whereas microvascular evaluation focused on a single standardized retrobulbar region of interest (ROI) to generate a global vascularity index with reduced sensitivity to motion-related artifacts.

Beyond elasticity assessment, SWE has also been applied to measuring optic nerve diameter in various ophthalmic conditions¹⁵. In this study, increasing AL was associated with a reduction in optic nerve diameter and significant retrobulbar microvascular alterations, whereas no corresponding changes in tissue stiffness were detected by SWE. Clinically, optic nerve diameter and retrobulbar microvascular parameters may provide more sensitive indicators of axial elongation than elastographic stiffness measurements alone, particularly in myopic eyes without advanced posterior pole deformation.

The age imbalance across the AL groups in the present study may reflect differences in patterns of clinical presentation within the study population. Younger individuals and patients with advanced myopia tended to undergo ophthalmologic evaluation more often, likely because of increased visual demands and more noticeable visual symptoms. In contrast, patients with mild to moderate myopia in middle age were less frequently seen in clinical practice in our region. This pattern may reflect a common misconception among middle aged patients regarding spectacle use and myopic progression, together with preserved near vision after the age of 40, which can lessen the perceived need for refractive correction or regular follow-up. Importantly, age was included as a covariate in multivariate analyses to account for this imbalance and to minimize its potential impact on the study outcomes.

A major strength of this study is the combined evaluation of retrobulbar biomechanical and microvascular parameters using SWE and a quantitative vascularity index, allowing a more comprehensive assessment of retrobulbar changes associated with axial elongation in myopic eyes. A limitation of this study is the exclusion of eyes with advanced pathologic myopia, including posterior staphyloma and myopic maculopathy with the Meta-Analysis for Pathologic Myopia (META-PM) category 3 or higher. Due to the markedly irregular posterior contour and advanced structural deformation associated with these features, standardized and reproducible SWE and microvascular measurements could not be reliably obtained. Therefore, the results primarily reflect myopic eyes without advanced, ultrasonographically apparent posterior pole deformation and should be interpreted accordingly. In addition, although the association between AL and vascularity index remained statistically significant after adjustment for age and sex, the relatively limited sample size and borderline p value warrant cautious interpretation, and larger studies are needed to confirm the robustness of this relationship.

In conclusion, axial elongation was associated with reduced retrobulbar vascularity, while SWE failed to detect parallel changes in tissue stiffness within the studied AL range. These findings suggest that retrobulbar microvascular alterations may occur before measurable biomechanical changes become detectable by SWE during axial elongation. This combined SWE and UMA approach may therefore contribute to a more comprehensive understanding of retrobulbar tissue changes associated with myopia.

Materials and methods

Study design

This prospective cross-sectional study was conducted collaboratively by the Departments of Ophthalmology and Radiology at Agri Ibrahim Cecen University Training and Research Hospital between October and December 2025. Ethical approval was obtained from the Clinical Research Ethics Committee of Atatürk University (approval number: 09; approval date: September 5, 2025), and the study was conducted in accordance with the principles of the Declaration of Helsinki. Written informed consent was obtained from all participants before enrollment.

Patient selection, ophthalmological examination, and group classification

Participants aged 18 years and older who underwent routine ophthalmologic examination at the Department of Ophthalmology were prospectively enrolled in the study. Exclusion criteria included a history of ocular trauma; previous ocular surgery; glaucoma; retinal or neuro-ophthalmic disorders other than pathological myopia; advanced pathologic myopia with clinically significant myopic maculopathy (META-PM category 3 or higher)¹⁶; hyperopic refractive error (SE ≥ + 0.25 diopters), due to potentially different biomechanical characteristics compared with myopic eyes; active ocular inflammation or infection; significant corneal pathology; severe dry eye syndrome, as ocular surface instability could affect refractive and optical biometry measurements and reduce examination tolerability during contact-based ultrasonographic assessment; pregnancy; and systemic diseases or use of medications that could potentially affect ocular structures.

Initially, demographic data were recorded for each eligible participant, followed by a comprehensive ophthalmological assessment. This assessment included measurement of BCVA using a Snellen chart, slit-lamp biomicroscopy (Zeiss, Oberkochen, Germany), intraocular pressure measurement with Goldmann applanation tonometry, measurement of cycloplegic spherical and cylindrical refractive error using an autorefractor-keratometer (RKT-7700, NIDEK, Co., Ltd., Gamagori, Japan). Then, fundus examination was performed in all participants, and AL was measured using optical biometry (Aladdin, Topcon, Tokyo, Japan). Snellen BCVA was converted to logarithm of the minimum angle of resolution (logMAR) units for statistical analysis. Spherical equivalent value was calculated as the spherical refractive error plus half of the cylindrical refractive error.

To avoid inter-eye correlation, a single eye was selected using simple randomization performed on a computer. A randomly generated value (0 or 1) was assigned to each subject, with values below 0.5 corresponding to the right eye and values of 0.5 or higher corresponding to the left eye. Eyes were categorized into three groups based on axial length. Group 1 comprised eyes with axial length shorter than 24.00 mm, Group 2 included eyes with axial length between 24.00 and 25.99 mm, and Group 3 consisted of eyes with axial length ≥ 26.00 mm. Because AL and refractive status are not fully interchangeable parameters, eyes with AL < 24.00 mm were eligible for inclusion provided that they did not meet the exclusion criterion for hyperopic refractive error. Patients with an AL difference greater than 2.00 mm between the two eyes were excluded.

The study was designed with a balanced group structure in order to be able to provide comparable statistical power across the three AL categories. Given the exploratory nature of the study and the limited availability of prior data on retrobulbar vascularity index measurements in myopic eyes, a formal a priori sample size calculation based on this parameter was not feasible. Therefore, we aimed to include at least 30 eyes in each group, which is generally considered adequate for preliminary intergroup comparisons and regression analyses. To allow for possible exclusions and to maintain balanced group sizes, 33 eyes were ultimately included in each group, as this was feasible within the study timeframe.

Ultrasonographic evaluation

Following the ophthalmological examination, the patients were referred to the Department of Radiology for ultrasonographic assessment and were informed about the procedure beforehand. All examinations were performed with the participants in the supine position and with their eyes closed. No supporting material was used to elevate the head, and a neutral head position was targeted. Participants were instructed to maintain a forward gaze without any ocular movement. Ultrasonographic evaluations were conducted using a Mindray Resona R9 ultrasound system (Mindray Bio-Medical Electronics, Shenzhen, China) equipped with an L15-3 WU linear array transducer (3.8–15.4 MHz), real-time SWE, and UMA software. Measurements included optic nerve diameter, SWE of the optic nerve and retrobulbar fat tissue, and assessments performed using UMA.

B-mode ultrasonography was performed without exerting pressure on the globe. The ultrasound probe was positioned horizontally, ensuring that the optic nerve was centered within the imaging plane. Optic nerve diameter was measured at a point 3 mm posterior to the globe using standardized techniques and recorded for analysis (Fig. 1A).

Fig. 1.

Ultrasonographic evaluation of the right eye of a 38-year-old female patient with an axial length of 24.02 mm. (A) Measurement of the optic nerve diameter performed 3 mm posterior to the globe, perpendicular to the optic nerve axis, using a standardized transorbital ultrasonography technique. (B) Shear wave elastography assessment of the optic nerve and adjacent retrobulbar fat tissue. A rectangular sampling box was positioned over the retrobulbar region, and circular regions of interest (ROIs) with a diameter of 3 mm were placed centrally within the optic nerve and within the adjacent retrobulbar fat tissue, and mean elasticity values (kPa) were recorded. (C) Ultra-microangiography image demonstrating assessment of retrobulbar microvascularity. A circular ROI with a diameter of 10 mm was centered on the optic nerve. Color pixel percentage was calculated as a quantitative vascularity index, representing the proportion of color-coded vascular signals within the ROI.

For SWE imaging, the vitreous body was excluded from the sampling area to minimize motion-related and acoustic artifacts. A rectangular sampling frame measuring approximately 3 × 2 cm was positioned over the retrobulbar optic nerve. Within this frame, a circular ROI with a diameter of 3 mm was placed centrally within the optic nerve to obtain elasticity measurements. After a stabilization period of 3–5 s, the image was frozen, and the system automatically calculated minimum, maximum, and mean SWE values of the optic nerve. The mean SWE value of the optic nerve was recorded as SWE-optic nerve. An additional circular ROI was positioned approximately 2 mm away from the optic nerve within the adjacent retrobulbar fat tissue, and the mean SWE value obtained from this region was recorded as SWE-fat tissue (Fig. 1B). The SWE ratio was calculated by dividing the SWE of the optic nerve by that of the retrobulbar fat tissue.

Tissue stiffness was displayed as a semi-transparent color map overlaid on the grayscale image, with elasticity values ranging from blue to red (0–75 kPa), with blue indicating the lowest elasticity and red indicating the highest elasticity.

All SWE measurements were obtained in 2D-SWE high-quality mode, ensuring a motion stability index of at least four stars and a maximum reliability index of the ultrasound system for elastography measurements (M-STB index) of five stars, indicating optimal image quality.

In addition to elasticity assessment, a vascularity index was obtained to assess microvascular characteristics within the retrobulbar region. Color pixel percentage, a quantitative UMA parameter reflecting the proportion of vascular structures within a predefined ROI^12,17,18, was used as the vascularity index. For CPP measurement (vascularity index), UMA mode was activated on the device and set to PRF 0.6 kHz, wall filter 63 Hz, and dynamic range 25 dB. A circular ROI with a diameter of 10 mm was positioned centrally over the retrobulbar region, with the optic nerve placed at the center of the ROI, while excluding the retinal/choroidal layers and ensuring that the vitreous body did not overlap with the measurement area. Using the subtraction UMA mode to minimize motion and background artifacts, the central retinal artery was aligned within the imaging field to optimize vascular visualization. After elimination of vascular artifacts, three consecutive measurements were obtained, and the mean CPP value of the retrobulbar tissue was recorded as the vascularity index (Fig. 1C).

The examination time and acoustic output during SWE and UMA assessments were kept as low as reasonably achievable, while maintaining adequate diagnostic image quality, in accordance with the ALARA (As Low As Reasonably Achievable) principle.

All ultrasonographic examinations were performed by a single experienced radiologist with 7 years of experience in orbital ultrasonography, 6 years of experience in SWE, and 1 year of experience in UMA, using a standardized acquisition protocol. The use of a single experienced operator was preferred to minimize inter-operator variability and improve measurement consistency across examinations. In addition, this approach was intended to minimize acoustic exposure to ocular tissues by avoiding repeated examinations by multiple operators.

Statistical analysis

Statistical analyses were performed using Statistical Package for the Social Sciences (SPSS) software, version 26.0 (IBM Corp., Armonk, NY, USA). Continuous and categorical variables were expressed as mean ± standard deviation (SD) and as number and percentage, respectively. Continuous variables were assessed for normality using the Shapiro-Wilk test.

Intergroup comparisons were conducted using one-way ANOVA for normally distributed data or the Kruskal–Wallis test for non-normally distributed data, as appropriate. For statistically significant intergroup differences, post hoc analyses were conducted using the independent samples t-test or the Mann–Whitney U test with Bonferroni correction applied. Categorical variables were compared using the Pearson chi-square test.

Associations between ultrasonographic parameters and clinical characteristics were assessed using Spearman’s correlation analysis. To evaluate independent associations between AL and ultrasonographic measurements, multivariate linear regression models were constructed, adjusting for age and sex as covariates.

A p value < 0.05 was considered statistically significant.

Author contributions

Concept: S.K., Y.O; Design: S.K., M.K., Y.O.; Supervision: E.K., S.Y.T.; Resource: M.I.I., O.P., and C.T.; Data Collection and/or Processing: S.K., M.K., M.I.I., C.T., O.P., E.K., S.Y.T., and Y.O.; Analysis and/or Interpretation: S.K., M.K., and Y.O.; Literature Search: S.K., and M.K.; Writing: S.K., M.K., M.I.I., C.T., O.P., E.K., S.Y.T., and Y.O.; Critical Reviews: S.K., M.K., M.I.I., C.T., O.P., E.K., S.Y.T., and Y.O.;

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.

Institutional review board statement

The study was conducted in accordance with the Declaration of Helsinki and approved by the institutional ethics committee (Approval number: 09 date: September 5, 2025).

Informed consent

Written informed consent was obtained from all participants prior to their inclusion in the study.