Effects of ptosis surgery on Schlemm canal and anterior chamber angle parameters assessed by anterior segment OCT

Abstract

Purpose

To evaluate changes in anterior segment morphology using anterior segment optical coherence tomography (AS-OCT) in patients undergoing levator surgery for ptosis and to investigate the potential influence of eyelid position changes on anterior segment parameters.

Methods

This study included 20 eyes of 18 patients who underwent levator surgery for ptosis. Eyelid parameters (MRD-1 and palpebral fissure height) and anterior segment measurements obtained by AS-OCT were recorded preoperatively and at postoperative weeks 4–6. Angle opening distance (AOD), trabecular iris space area (TISA), iridocorneal angle (ICA), Schlemm canal length (SCL), and Schlemm canal area (SCA) were measured in nasal and temporal quadrants.

Results

Postoperatively, MRD-1 and PFH increased statistically significantly (p < 0.001 for both). Among anterior segment parameters, a significant postoperative decrease was observed only in nasal SCL (p = 0.008), with a moderate-to-large effect size (r = 0.419). No significant differences were detected in AOD, TISA, ICA, or SCA measurements in either nasal or temporal quadrants (p > 0.05). Nasal ICA demonstrated a borderline postoperative increase (p = 0.086; r = 0.271). Correlation analysis revealed a significant negative association between nasal AOD change and both MRD-1 and PFH changes.

Conclusion

Levator surgery for ptosis may be associated with subtle anterior segment morphologic changes detectable by AS-OCT. In particular, the observed decrease in nasal SCL should be regarded as an exploratory, hypothesis-generating finding that requires confirmation in larger studies.

Introduction

Ptosis is a common oculopalpebral condition characterized by the downward displacement of the upper eyelid below its normal anatomical position, leading to both functional and cosmetic consequences. In moderate to severe cases, visual field obstruction, compensatory head posture changes, and aesthetic concerns often necessitate surgical treatment. Surgical correction of ptosis involves not only soft tissue repositioning but also alterations in eyelid tension and mechanical forces acting on the globe.

The levator palpebrae superioris muscle and the superior rectus muscle share a common embryological origin, differentiating during fetal development to form separate muscular structures [1]. The levator muscle subsequently gives rise to the levator aponeurosis, which inserts into the developing tarsal plate and anterior orbital septum, establishing the anatomical basis for eyelid elevation [1].

It is well established that the upper eyelid exerts mechanical pressure on the cornea and limbal region, which may influence the ocular surface and anterior segment morphology [2]. Previous studies have shown that changes in eyelid position may lead to measurable anatomical alterations in anterior segment structures due to the reduction of eyelid induced pressure [3]. However, most of the existing literature has primarily focused on changes in corneal topography, astigmatism, and visual acuity following ptosis surgery, while the potential effects of surgically increased palpebral aperture on deeper anterior segment structures remain insufficiently explored.

Recent advances in anterior segment optical coherence tomography (AS-OCT) technology have enabled quantitative morphometric assessment of the anterior segment [4]. Using this technique, the configuration of the iridocorneal angle and structural characteristics of the trabecular region can be evaluated noninvasively with high resolution. Moreover, morphological parameters related to the aqueous humor outflow pathway can be quantitatively assessed [5, 6]. These technological developments have made it possible to quantitatively investigate the potential effects of eyelid surgeries beyond cosmetic or visual field improvements, including their influence on anterior segment morphology.

The aim of the present study was to evaluate possible morphologic changes in anterior segment parameters using AS-OCT in patients undergoing levator surgery for ptosis and to explore the relationship between eyelid position changes and anterior segment configuration.

Methods

Study design

This retrospective study was approved by the Ethics Committee of Kartal Dr. Lütfi Kırdar City Hospital (Decision No: 2026/010.99/24/5) and was conducted in accordance with the principles of the Declaration of Helsinki. Medical records and AS-OCT images of patients who underwent ptosis surgery for cosmetic or functional indications at the Oculoplastic Surgery Clinic of Kartal Dr. Lütfi Kırdar City Hospital between 2024 and 2025 were retrospectively reviewed.

Patients with a history of previous ocular surgery, glaucoma, uveitis, or chronic ocular surface disease were excluded from the study. All participants underwent a comprehensive ophthalmologic examination prior to surgery, including best corrected visual acuity assessment and slit lamp biomicroscopy of the anterior and posterior segments.

Eyelid parameters, including palpebral fissure height (PFH), levator function, and margin reflex distance-1 (MRD-1), were recorded preoperatively and during the follow-up period between 4 and 6 weeks postoperatively, following the complete resolution of eyelid edema and ecchymosis. Of the 20 eyes included, three unilateral cases had congenital ptosis, while the remaining cases (both unilateral and bilateral) had aponeurotic ptosis. Levator function was greater than 10 mm in all patients.

Surgical procedure

All surgeries were performed by the same experienced surgeon (A.A.) under operating room conditions. Local anesthesia was achieved by infiltration of a solution containing 2% lidocaine with 1:100,000 epinephrine along the eyelid crease.

After exposure of the tarsal plate, the levator aponeurosis was identified and dissected. Hemostasis was achieved with cauterization when necessary. Levator advancement was then performed according to the required correction, and the aponeurosis was reattached to the tarsus using 6−0 polyglactin sutures. During the procedure, patients were positioned upright to optimize eyelid height and symmetry. Skin closure was completed using 6−0 polyglactin sutures, and all patients were instructed to apply cold compresses during the first 72 postoperative hours.

Anterior segment optical coherence tomography imaging

Anterior segment imaging was performed using a swept-source optical coherence tomography device (Topcon Triton DRI-OCT; Topcon Corp., Tokyo, Japan) equipped with an anterior segment module. The device operates at a wavelength of 1050 nm, with a scanning speed of 100 kHz and a scanning depth of 3 mm.

To minimize diurnal variation, all measurements were obtained in the morning under dim lighting conditions by the same examiner (A.A.). Images were captured from the nasal and temporal quadrants (corresponding to the 3 and 9 o’clock positions). During imaging, patients were instructed to fixate in the opposite direction to facilitate visualization of the target limbal region. No manual manipulation of the eyelids was performed, and images were obtained with the eyelids in their natural position.

In some preoperative cases with severe ptosis where MRD-1 was below zero and imaging from the 3 and 9 o’clock positions was not possible in the natural position, patients were asked to open their eyes to allow adequate visualization. For each quadrant, at least three images were obtained, and the highest-quality image with clear visualization of the scleral spur and Schlemm canal was selected.

Image analysis

OCT images were exported from the Topcon IMAGEnet software and analyzed using ImageJ software (National Institutes of Health, Bethesda, MD, USA). All measurements were performed using the scleral spur as the reference landmark (Fig. 1).

Fig. 1.

Representative swept-source anterior segment OCT image demonstrating measurement of anterior chamber angle parameters. The scleral spur (SS) was used as the anatomical reference landmark. Angle opening distance(AOD) and trabecular iris space area(TISA) were measured 500 μm anterior to the scleral spur. The asterisk (*) indicates the manually delineated area corresponding to the Schlemm canal used for measurement of Schlemm canal area (SCA). The upper image shows the external view of the right eye indicating the temporal quadrant used for OCT imaging

The following parameters were evaluated:

• Angle Opening Distance (AOD500): the perpendicular distance from the corneal endothelium to the iris surface at a point located 500 μm anterior to the scleral spur.

• Trabecular Iris Space Area (TISA500): the area bounded by the scleral spur, the point on the corneal endothelium 500 μm anterior to the scleral spur, a perpendicular line from this point to the iris surface, and the iris surface.

• Iridocorneal Angle (ICA): the angle formed between the corneal endothelium and the iris surface at a location 500 μm anterior to the scleral spur.

• Schlemm’s Canal Parameters: the widest horizontal diameter of the canal was recorded as Schlemm canal length (SCL), and the luminal area was measured using the freehand selection tool and recorded as Schlemm canal area (SCA).

To minimize measurement error, all morphometric measurements were repeated three times, and the mean values were used for statistical analysis.

Statistical analysis

Statistical analyses were performed using SPSS software (version 23.0; IBM Corp., Armonk, NY, USA). Normality of data distribution was assessed using the Shapiro–Wilk test. As most variables did not demonstrate normal distribution, preoperative and postoperative measurements were compared using the Wilcoxon signed-rank test. Correlations between changes in eyelid parameters and anterior segment measurements were evaluated using Spearman correlation analysis. Linear regression analysis was performed to determine whether changes in eyelid position were associated with changes in anterior segment parameters. For regression models, residual normality and homoscedasticity were assessed; assumptions were adequately met for the ΔPFH model, while the ΔMRD-1 model showed a mild deviation from normality, consistent with the exploratory nature of the analysis. Cluster-robust standard errors, incorporating a small-sample correction, were computed using Python (version 3.12; statsmodels library, version 0.15) as a sensitivity check for inter-eye correlation. A p-value < 0.05 was considered statistically significant.

Results

A total of 20 eyes from 18 patients were included in the study. Eight patients were male and ten were female, with a mean age of 53.11 ± 15.75 years. Ten eyes were right eyes and ten were left eyes. Preoperative MRD-1 and PFH were 0.4 ± 1.5 mm and 5.35 ± 1.53 mm, respectively. Postoperatively, these values increased to 3.45 ± 1.05 mm and 8.4 ± 1.31 mm, demonstrating significant postoperative improvement following levator surgery (p < 0.001 for both parameters).

Preoperative and postoperative anterior segment parameters measured by AS-OCT are summarized in Table 1. Among these parameters, a statistically significant postoperative decrease was observed only in nasal SCL (p = 0.008). No significant differences were detected in other anterior segment parameters, including AOD, TISA, ICA or SCA, in either nasal or temporal quadrants (p > 0.05 for all comparisons). The decrease in nasal SCL demonstrated a moderate-to-large effect size (r = 0.419). Although nasal ICA did not reach statistical significance (p = 0.086), it showed a small-to-moderate effect size (r = 0.271). Effect sizes for the remaining parameters were negligible.

Table 1.

Preoperative and postoperative anterior segment parameters measured by AS-OCT

	Preoperative	Postoperative	P value	Effect size (r)
Nasal AOD	405,35±183,64	419,25±235,25	0,881	0,023
Nasal ICA	32,1 ± 10,17	34,39 ± 12,18	0,086	0,271
Nasal TISA	0,170 ± 0,068	0,167 ± 0,091	0,390	0,135
Nasal SCL	292 ± 74,82	228,6 ± 50,41	0,008	0,419
Nasal SCA	4566,35 ± 2131,18	4501,35 ± 1909,21	0,654	0,07
Temporal AOD	445,55 ± 168,6	441,15 ± 195,42	0,896	0,02
Temporal ICA	34,04 ± 13,49	35,1 ± 12,45	0,391	0,135
Temporal TISA	0,169 ± 0,074	0,160 ± 0,075	0,765	0,047
Temporal SCL	230 (192,75–289)	214,5 (191,5-250,5)	0,173	0,215
Temporal SCA	5248,05 ± 2431,65	5110,05 ± 2293,33	0,852	0,029

AOD: Angle opening distance; TISA: Trabecular iris space area; ICA: Iridocorneal angle; SCL: Schlemm canal length; SCA: Schlemm canal area

Correlation analyses between eyelid position changes and anterior segment parameters are presented in Table 2. A significant negative correlation was observed between nasal AOD change and both MRD-1 and PFH changes (r = − 0.463, p = 0.04; r = − 0.553, p = 0.011, respectively). No significant correlations were identified between eyelid position changes and other anterior segment parameters.

Table 2.

Correlation of angle parameters with changes in eyelid position

	ΔMRD-1	ΔPFH
ΔNasal AOD	-0,463 p = 0,04	-0,553 p = 0,011
ΔNasal ICA	-0,088 p = 0,713	-0,131 p = 0,583
ΔNasal TISA	-0,249 p = 0,289	-0,291 p = 0,213
ΔNasal SCL	0,013 p = 0,955	-0,039 p = 0,869
ΔNasal SCA	-0,128 p = 0,592	-0,151 p = 0,525
ΔTemporal AOD	-0,115 p = 0,628	-0,073 p = 0,758
ΔTemporal ICA	0,143 p = 0,547	0,270 p = 0,250
ΔTemporal TISA	-0,286 p = 0,222	-0,291 p = 0,213
ΔTemporal SCL	-0,140 p = 0,555	-0,164 p = 0,488
ΔTemporal SCA	-0,132 p = 0,578	-0,049 p = 0,837

MRD: Margin reflex distance-1; PFH: Palpebral fissure height; Δ: Postoperative – preoperative difference; AOD: Angle opening distance; TISA: Trabecular iris space area; ICA: Iridocorneal angle; SCL: Schlemm canal length; SCA: Schlemm canal area

Linear regression analysis was performed to determine whether eyelid position changes were associated with changes in nasal AOD. Changes in MRD-1 were significantly associated with changes in nasal AOD (B = − 45.3 μm per 1-mm increase; 95% CI: −90.3 to − 0.4; p = 0.048), explaining approximately 20% of the variance in AOD change (R² = 0.20); this association attenuated after accounting for inter-eye correlation (see below). Similarly, PFH change showed a relatively stronger association with nasal AOD change (B = − 51.5 μm per 1-mm increase; 95% CI: −91.8 to − 11.2; p = 0.015), accounting for approximately 28.6% of the variance (R² = 0.286).

To assess the robustness of these findings, three sensitivity analyses were performed. First, because two patients contributed both eyes, the primary analysis was repeated after excluding one eye from each of these patients (n = 18); the nasal SCL decrease remained statistically significant (p = 0.011). Second, excluding eyes that required voluntary eyelid opening prior to imaging (n = 14) yielded consistent findings, with the nasal SCL decrease remaining significant (p = 0.0085) and the regression associations retained (ΔMRD-1: p = 0.020; ΔPFH: p = 0.017). Third, to further account for inter-eye correlation, key comparisons and regression models were repeated using cluster-robust standard errors clustered by patient; the nasal SCL decrease remained significant (p = 0.004), as did the association between ΔPFH and Δnasal AOD (p = 0.018), whereas the association between ΔMRD-1 and Δnasal AOD attenuated (p = 0.092).

Scatter plots illustrating the relationships between ΔMRD-1 and Δnasal AOD as well as ΔPFH and Δnasal AOD are shown in Figs. 2 and 3.

Fig. 2.

Scatter plot illustrating the association between ΔMRD-1 and Δnasal AOD. The linear regression line with 95% confidence interval is shown (R² = 0.20, p = 0.048)

Fig. 3.

Linear regression analysis showing the relationship between ΔPFH and Δnasal AOD. The regression line with 95% confidence interval is displayed (R² = 0.286, p = 0.015)

Discussion

In the present study, the effects of levator surgery on anterior segment morphology were quantitatively evaluated using swept-source AS-OCT. The significant postoperative increases in MRD-1 and PFH confirmed successful elevation of the upper eyelid and enlargement of the palpebral aperture. Beyond functional improvement, our findings suggest that levator surgery may be associated with subtle morphologic changes in anterior segment structures detectable by AS-OCT.

The upper eyelid is known to exert a continuous mechanical influence on the ocular surface [7]. Previous studies have demonstrated that eyelid pressure and eyelid manipulation may affect ocular biomechanics and intraocular pressure measurements [3, 8–10]. Voluntary eyelid squeezing and manual eyelid manipulation during tonometry have both been associated with increased intraocular pressure measurements, while postoperative intraocular pressure changes have also been reported following upper eyelid blepharoplasty [8–10]. Collectively, these findings support the concept that eyelid position and eyelid–globe interaction may influence anterior segment configuration.

To our knowledge, no previous study has directly evaluated the effect of eyelid position or eyelid surgery on Schlemm canal morphology. However, previous studies suggest that Schlemm canal dimensions may be responsive to biomechanical alterations. Digital ocular massage has been associated with enlargement of Schlemm canal dimensions, while altered canal morphology has also been reported in conditions such as Graves’ ophthalmopathy and after cataract surgery [11–14]. Collectively, these findings support the concept that Schlemm canal morphology may demonstrate dynamic structural responses to changes in ocular mechanical environment.

In the present study, a significant postoperative decrease in nasal SCL was observed, with a moderate-to-large effect size. Schlemm canal morphology is known to be influenced by multiple biomechanical factors, including intraocular pressure and trabecular meshwork tension [15, 16]. Changes in eyelid position after levator surgery may alter eyelid–globe mechanical interaction and contribute to subtle morphologic changes in the trabecular region. However, regression analysis did not demonstrate a significant linear association between eyelid elevation and SCL change, suggesting that the relationship may be multifactorial. In addition, the relatively small sample size may have limited the detection of more subtle associations. This observational finding does not establish a causal effect of levator surgery on Schlemm canal morphology and should be interpreted as an association warranting further investigation.

Interestingly, despite the significant decrease in SCL, no significant change was observed in SCA. This finding may suggest that levator surgery influences certain morphologic aspects of Schlemm canal configuration without a measurable change in luminal area. Because SCL and SCA represent different structural characteristics of the canal, they may demonstrate different response patterns following alterations in eyelid position and mechanical interaction with the globe.

Previous studies have reported that eyelid surgery may induce changes in corneal curvature, anterior chamber parameters, and iridocorneal angle configuration [3, 17–19]. However, the reported findings have been variable, with some studies demonstrating measurable anterior segment alterations while others observed minimal or no significant biometric changes. These heterogeneous results suggest that the effects of eyelid surgery on anterior segment structures may depend on surgical technique, eyelid tension, and individual biomechanical characteristics.

In our study, nasal AOD demonstrated a significant inverse association with eyelid position changes, with regression analysis indicating that each 1-mm increase in palpebral fissure height was associated with an approximate 51-µm decrease in nasal AOD. This finding suggests that eyelid elevation may be associated with subtle alterations in peripheral anterior segment configuration, although the underlying relationship is likely multifactorial. In addition, nasal ICA values demonstrated a borderline postoperative increase with a small-to-moderate effect size, suggesting a possible effect of surgery on angle configuration. However, the limited sample size may have reduced the statistical power to detect statistically significant changes.

Another notable finding was that the observed changes were more pronounced in the nasal quadrant, while temporal parameters remained largely unchanged. The reasons for this apparent nasal predominance remain unclear. Possible explanations, including regional anatomical differences, scleral rigidity variations, or regional differences in eyelid-related mechanical effects, remain hypothetical because these mechanisms were not directly assessed in the present study [2, 20]. Because AS-OCT imaging was limited to nasal and temporal quadrants, potential superior quadrant changes, where eyelid influence may be more direct, could not be evaluated.

The strengths of this study include the use of high-resolution swept-source AS-OCT imaging, standardized measurement conditions, and repeated morphometric measurements performed by the same examiner. In addition, effect size and regression analyses allowed a more comprehensive interpretation of subtle morphologic findings. Nonetheless, several limitations should be noted. The sample size was relatively small and no a priori power calculation was performed, as this retrospective study was exploratory in nature. The limited sample size may have reduced the statistical power to detect smaller effects. In addition, the relatively short follow-up period may have limited the detection of longer-term changes. Formal intraobserver and interobserver reproducibility of the manual ImageJ measurements was not assessed. Although each parameter was measured three times and the mean value was used for analysis, observer-dependent measurement variability cannot be excluded, particularly for the manually delineated Schlemm canal parameters. In six eyes with severe preoperative ptosis, as adequate visualization could not be obtained in the natural eyelid position; this maneuver may transiently alter eyelid–globe contact pressure and anterior segment configuration, potentially introducing measurement bias. However, a sensitivity analysis excluding these eyes yielded consistent results suggesting this bias did not substantially affect the main findings. As multiple parameters were compared without adjustment for multiple testing, the isolated significance of nasal SCL should be interpreted cautiously as exploratory and hypothesis-generating. Furthermore, this study did not include an untreated control group; therefore, temporal variation, measurement variability, or regression to the mean cannot be entirely excluded as alternative explanations for the observed changes. Additionally, intraocular pressure was not measured and glaucoma patients were excluded, limiting correlation of structural changes with functional outflow parameters. Overall, these findings suggest that periocular surgical procedures may be associated with subtle anterior segment morphologic alterations detectable by AS-OCT, although the clinical relevance of these findings remains to be clarified.

Author contributions

A.A.: Conceptualization, Methodology, Investigation, Data Curation, Formal Analysis, Visualization, Writing – Original Draft, Writing – Review & Editing. F.I.S.D.: Investigation, Resources, Data Curation.

Funding

The authors received no financial support for the research.

Data availability

The datasets are available from the corresponding author on reasonable request.

Declarations

Ethical approval

This study was approved by the Ethics Committee of Kartal Dr. Lütfi Kırdar City Hospital (Decision No: 2026/010.99/24/5) and was conducted in accordance with the principles of the Declaration of Helsinki.

Consent to participate

Due to the retrospective nature of the study, formal informed consent to participate was not required according to institutional policy and Ethics Committee regulations.

Consent for publication

Not applicable. No identifiable personal information or images are included in this manuscript.

Competing interests

The authors declare no competing interests.