Swept-source optical coherence tomography assessment of Schlemm’s canal after phacoemulsification with goniosynechialysis in Chinese patients with primary angle-closure glaucoma
IntroductionOther Section
Primary angle-closure glaucoma (PACG) is a leading cause of irreversible blindness worldwide (1). Asian patients comprise 87% of all PACG patients worldwide, and China has the highest incidence of PACG worldwide (2). Angle closure is characterized by the blockage of aqueous outflow due to the mechanical contact of the iris with trabecular meshwork (TM). As 75–80% of aqueous humor outflow occurs via the conventional TM-Schlemm’s canal (SC) pathway (3), peripheral anterior synechiae (PAS) can impede the aqueous humor outflow, resulting in elevated intraocular pressure (IOP). Acute and chronic forms of PACG are further classified according to the clinical features of the disease. Patients with acute primary angle-closure glaucoma (APACG) experience a sudden increase in IOP as the iris rapidly covers the TM. Conversely, patients with chronic primary angle-closure glaucoma (CPACG) experience a slow and asymptomatic increase in IOP as the iris gradually covers the TM (4-6).
The treatment of PACG varies depending on the severity of the angle closure. When the degree of PAS is mild, laser peripheral iridotomy, phacoemulsification alone, or in combination with topical IOP-lowering drops, is often used to lower IOP (7). Further surgical intervention, including combined phacoemulsification with goniosynechialysis (phaco-GSL) or trabeculectomy, is usually required when extensive PAS develops. Combined phaco-GSL has been reported to be an effective treatment for angle-closure glaucoma (8-10), which involves the removal of cataracts and the separation of the PAS to restore the normal outflow pathway. However, it is not yet known whether the TM-SC pathway functions normally after the PAS obstruction is removed. It has been suggested that SC plays an important role in the regulation of IOP in human eyes, with correlation studies indicating that fluctuations in IOP may be related to variations in SC size (11). A previous study also indicated that the eyes of PACG patients had smaller SCs than those of healthy individuals (12). However, the features of the morphology of SC in PACG eyes after phaco-GSL surgery are still unknown.
Anterior-segment optical coherence tomography (AS-OCT) is a fast and non-invasive examination that enables the real-time visualization and assessment of the SC. Several studies have used optical coherence tomography (OCT) to perform in vivo SC imaging, and reported that the SC appears as a thin, black lucent space in the deeper area of the corneoscleral limbus (13-15). In this study, we sought to observe whether structural changes occur in the SC in the eyes of patients with PACG (both APACG and CPACG) undergoing phaco-GSL surgery, and to study the possible factors associated with changes in the SC. We present this article in accordance with the STROBE reporting checklist (available at https://qims.amegroups.com/article/view/10.21037/qims-24-269/rc).
MethodsOther Section
In total, 35 patients (35 eyes) with APACG and 35 patients (35 eyes) with CPACG were recruited from the Eye, Ear, Nose, and Throat Hospital of Fudan University from December 2021 to December 2022. The study was conducted in accordance with the Declaration of Helsinki (as revised in 2013), and was approved by the Ethics Committee of the Eye, Ear, Nose, and Throat Hospital of Fudan University (No. 2021078). Written informed consent was obtained from all participants.
APACG was defined as follows: (I) a history of at least two typical symptoms (i.e., ocular or periocular pain, nausea or vomiting, and/or intermittent blurring of vision with halos); (II) an IOP spike >30 mmHg; (III) the presence of at least three signs (i.e., obvious conjunctival hyperemia, corneal epithelial edema, med-dilated pupil, and/or shallow anterior chamber); (IV) an occluded angle confirmed by gonioscopic examination; and (V) glaucomatous optic neuropathy or visual field defect. CPACG was defined as follows: (I) the absence of acute attack symptoms or signs; (II) PAS confirmed by gonioscopy; (III) a chronically elevated IOP (>21 mmHg); and (IV) glaucomatous optic neuropathy or visual field defect.
Based on the APACG and CPACG definitions provided above, patients were enrolled in the study if they met the following criteria: (I) had concurrent cataracts; (II) had ≥180 degrees of synechial angle closure; and (III) had logarithm of minimum angle of resolution (logMAR) visual acuity (VA) of 0.1 or worse. Patients were excluded from the study if they met any of the following exclusion criteria: (I) had secondary glaucoma; and/or (II) had undergone any type of ocular incisional surgery. If both eyes of one patient met the inclusion criteria, one eye was randomly selected. Patients in both the APACG and CPACG groups were initially treated with appropriate medications to lower IOP. These medications included intravenous mannitol, topical pilocarpine, timolol, acetazolamide, and brimonidine. All topical ocular medications were continued until the time of the surgery.
Complete ophthalmologic examinations were performed on all patients enrolled in this study, including best-corrected visual acuity (BCVA) in logMAR, the refractive error, slit-lamp examination, Goldmann applanation tonometry, visual field testing (Humphrey perimetry), axial length measurement using IOLmaster (Carl Ziess, Inc., Jena, Germany), and anterior-segment imaging by AS-OCT (see below). Gonioscopy was performed using a gonioscope (Volk Optical, Inc., Mentor, OH, USA), and the anterior chamber angle (ACA) was graded using the modified Shaffer grading system by a glaucoma specialist (Y.C.). In addition, medical and family histories were also collected for each patient. Patients underwent regular follow-ups at 1 week, 1 month, 3 months, and 6 months after surgery at the Glaucoma Clinic. Slit-lamp examination, BCVA, IOP measurements, and OCT were performed at each follow-up visit.
OCT data acquisition and processing
The AS-OCT instrument used in this study was swept-source optical coherence tomography (SS-OCT; CASIA SS-1000; Tomey Corporation, Nagoya, Japan) with a wavelength of 1,310 nm, a scan speed of 30,000 A-scans per second, and lateral resolution of 10 µm. A high-density (HD) angle scan (with a raster of 64 B-scans each with 512 A-scans over 8 mm) and a low-density (LD) scan (with a raster of 128 radial scans each with 512 A-scans over 16 mm) were acquired by SS-OCT. The nasal and temporal quadrants (at the 3 and 9 o’clock positions) were scanned independently. In the LD protocol, images of the temporal and nasal angles were acquired concurrently in a horizontal image centered on the cornea. In the HD protocol, patients were instructed to stare at a nasal or temporal fixation light to ensure that the iridocorneal angle was centered in the visual field of OCT. Next, the patients were advised to open their eyes as wide as possible when testing. If necessary, the examiner would help them to keep their eyes open with their fingers, without putting any pressure on the eye. Three scans were taken at each location. The highest-quality image at each location was selected for the final analysis. The digital images were processed by two masked operators (H.H. and F.G.) with more than 3 years’ experience in OCT using the software built into the apparatus. Due to the instability of patients’ conditions one week after surgery, only the images obtained after the first month of postoperative recovery were analyzed.
The SC appears as a thin, black lucent space located outside the TM in the AS-OCT images (Figure 1). The Schlemm’s canal diameter (SCD) was measured from the posterior to the anterior SC endpoints on the HD images. The Schlemm’s canal area (SCA) was drawn freehand and illustrated as the area surrounded by its boundary. The mean nasal and temporal SC measurements from each OCT image were used in the analysis.
The angle opening distance at 500 µm (AOD 500), trabecular-iris space area at 500 µm (TISA 500), and trabecular-iris angle at 500 µm (TIA 500) were automatically analyzed after the manual location of the scleral spur using the LD scan protocol. The AOD 500 was defined as the distance from the posterior surface of the cornea to the anterior surface of the iris, on a line perpendicular to the TM at 500 µm from the scleral spur. The TISA 500 was a trapezoidal area, defined by the following boundaries: anteriorly, by the AOD 500; posteriorly, by a line drawn from the perpendicular to the plane of the inner scleral wall to the iris; superiorly, by the inner corneoscleral wall; and inferiorly, by the iris surface. The TIA 500 was defined as an angle between the apex of the iris recess and the arms of the angle that pass through a point on the TM, located at a distance of 500 µm from the scleral spur and the point on the iris that is perpendicularly opposite. The anterior chamber depth (ACD) was defined as the perpendicular distance between the corneal endothelium at the corneal apex to the anterior lens surface.
Surgical procedure
The phaco-GSL surgeries were performed by an experienced ophthalmologist with more than 10 years’ experience in glaucoma. Briefly, after the administration of topical anesthesia, a standard clear-cornea tunneled phacoemulsification procedure was performed, and a foldable intraocular lens was then implanted in the capsular bag. Subsequently, a blunt cyclodialysis spatula was applied and pressed against the peripheral edges of the iris to remove any visible PAS. This procedure was repeated along the entire peripheral iris until the entire angle was fully open under gonioscopic observation. The residual viscoelastic was extracted at the end of the operation. After surgery, patients were administered steroids and antibiotics.
Data analysis
If both eyes of one patient met the inclusion criteria, one eye was selected at random for the analysis. The Kolmogorov-Smirnov normality test was used to examine whether the variables were normally distributed. The normally distributed continuous data are presented as the mean ± standard deviation (SD), and the categorical variables are presented as the count and percentage for each category. The non-normally distributed data are expressed as the median and interquartile range. An independent sample t-test (continuous data) or chi-square test (categorical data) was used to compare differences between groups. A Pearson’s correlation analysis was used to assess the association between the SC and the ocular parameters. A multiple linear regression analysis was conducted to examine predictors of change in the SC parameters from the baseline to 6 months after surgery (hereafter referred to as ∆SCD or ∆SCA), using parameters that showed significance of less than the 0.1 level in Pearson’s correlation analysis. The intraclass correlation coefficient (ICC), which assesses the variability of measurements between different participants, was calculated using the random-effects mixed model. All the statistical analyses were performed using SPSS software (SPSS Statistics version 22.0; IBM Corp., Armonk, NY, USA). A two-sided P value <0.05 was considered statistically significant.
ResultsOther Section
Demographic characteristics of patients
A total of 70 PACG patients (70 eyes) who met the criteria for phaco-GSL (Figure 2), were included in this study. Of the PACG patients, 35 had APACG (35 eyes, 50%) and 35 had CPACG (35 eyes, 50%). The mean age (mean ± SD) of the APACG and CPACG groups was 63.8±7.7 and 63.2±8.3 years, respectively (P>0.05). The APACG group comprised 9 (25.71%) males and 26 (74.29%) females, while the CPACG group comprised 17 (48.57%) males and 18 (51.43%) females (P=0.048). The APACG group had a significantly smaller cup-to-disc ratio (C/D) (0.54±0.18 vs. 0.71±0.21, P<0.001), smaller disease duration (2 vs. 12 months, P<0.001), shorter axial length (AL) (22.19±0.69 vs. 22.79±1.01 mm, P=0.005), and larger pupil diameter (4.27±1.39 vs. 2.65±0.93 mm, P<0.001) than the CPACG group. There were no significant differences in the laterality, mean deviation (MD), PAS range, refraction, central corneal thickness (CCT), lens thickness (LT), and IOP between the two groups (P>0.05). Detailed data are provided in Table 1.
Table 1
Parameters | APACG | CPACG | P value |
---|---|---|---|
Number of eyes | 35 (50.0) | 35 (50.0) | – |
Age (years) | 63.8±7.7 | 63.2±8.3 | 0.744 |
Male/female | 9/26 | 17/18 | 0.048†* |
Right/left eye | 14/21 | 18/17 | 0.337† |
C/D | 0.54±0.18 | 0.71±0.21 | <0.001* |
MD (dB) | –12.77±7.04 | –6.52±9.49 | 0.067 |
Disease duration (months) | 2 [1] | 12 [34] | <0.001* |
PAS range (degrees) | 253.71±91.85 | 230.57±82.25 | 0.271 |
Refraction (D) | 0.96±0.94 | 0.90±1.06 | 0.813 |
Axial length (mm) | 22.19±0.69 | 22.79±1.01 | 0.005* |
CCT (μm) | 548.14±31.25 | 538.69±31.96 | 0.215 |
LT (mm) | 4.96±0.36 | 4.85±0.32 | 0.189 |
IOP (mmHg) | 22.0±9.5 | 21.7±7.1 | 0.743 |
Pupil diameter (mm) | 4.27±1.39 | 2.65±0.93 | <0.001* |
Number of antiglaucoma medications | 2.7±0.8 | 2.9±0.8 | 0.385 |
Data are presented as n (%) or mean ± standard deviation, number or median [interquartile range]. †, chi-square test; *, P<0.05 indicates statistical significance. APACG, acute primary angle-closure glaucoma; CPACG, chronic primary angle-closure glaucoma; C/D, cup-to-disc ratio; MD, mean deviation; PAS, peripheral anterior synechiae; D, diopters; CCT, central corneal thickness; LT, lens thickness; IOP, intraocular pressure.
Changes in the ocular parameters before and after surgery
All the patients were followed up at 1 week, 1 month, 3 months, and 6 months after the surgery. In our within-group analysis, we found that all the postoperative parameters improved significantly compared with the preoperative parameters (all P<0.01). The IOPs were significantly lower at all follow-ups postoperatively compared with those at the baseline (all P<0.01) (Table 2). The IOP dropped from 22.0±9.5 mmHg preoperatively to 13.1±3.3 mmHg in the APACG group and from 21.7±7.1 mmHg to 13.8±3.4 mmHg in the CPACG group at the last follow-up, respectively. However, at the final follow-up examination, there was no significant difference in the mean reduction of the postoperative IOP between the APACG and CPACG groups (8.9±9.2 vs. 8.0±7.4 mmHg). In addition, the APACG group showed a greater improvement in logMAR VA than the CPACG group (0.48±0.41 vs. 0.31±0.22, P=0.037).
Table 2
Parameters | APACG | CPACG | P value |
---|---|---|---|
Preoperative logMAR VA | 0.63±0.50 | 0.40±0.26 | 0.019* |
1 week post operation | 0.30±0.34 | 0.23±0.24 | 0.298 |
1 month post operation | 0.19±0.27 | 0.15±0.13 | 0.370 |
3 months post operation | 0.17±0.28 | 0.11±0.11 | 0.257 |
6 months post operation | 0.16±0.27 | 0.09±0.11 | 0.192 |
∆logMAR VA | 0.48±0.41 | 0.31±0.22 | 0.037* |
Preoperative IOP (mmHg) | 22.0±9.5 | 21.7±7.1 | 0.871 |
1 week post operation | 14.0±4.2 | 15.6±5.6 | 0.177 |
1 month post operation | 14.9±5.3 | 15.6±5.3 | 0.652 |
3 months post operation | 13.6±4.2 | 13.9±4.1 | 0.776 |
6 months post operation | 13.1±3.3 | 13.8±3.4 | 0.428 |
∆IOP | 8.9±9.2 | 8.0±7.4 | 0.631 |
Preoperative ACD (mm) | 1.71±0.22 | 1.90±0.19 | <0.001* |
1 month post operation | 3.23±0.18 | 3.33±0.29 | 0.081 |
3 months post operation | 3.26±0.20 | 3.36±0.26 | 0.086 |
6 months post operation | 3.34±0.21 | 3.39±0.22 | 0.273 |
∆ACD | 1.63±0.31 | 1.50±0.29 | 0.070 |
Preoperative AOD 500 (mm) | 0.12±0.06 | 0.16±0.05 | 0.012* |
1 month post operation | 0.31±0.09 | 0.30±0.06 | 0.867 |
3 months post operation | 0.34±0.07 | 0.35±0.08 | 0.486 |
6 months post operation | 0.36±0.07 | 0.35±0.08 | 0.792 |
∆AOD | 0.23±0.06 | 0.19±0.09 | 0.044* |
Preoperative TISA 500 (mm2) | 0.05±0.04 | 0.07±0.03 | 0.019* |
1 month post operation | 0.12±0.04 | 0.12±0.03 | 0.964 |
3 months post operation | 0.13±0.04 | 0.13±0.03 | 0.596 |
6 months post operation | 0.15±0.04 | 0.13±0.03 | 0.057 |
∆TISA | 0.10±0.05 | 0.06±0.03 | 0.001* |
Preoperative TIA 500 (degrees) | 13.46±4.23 | 14.87±4.39 | 0.173 |
1 month post operation | 30.04±7.53 | 26.91±4.81 | 0.042* |
3 months post operation | 31.00±6.04 | 30.65±6.85 | 0.822 |
6 months post operation | 32.57±5.68 | 31.14±5.84 | 0.301 |
∆TIA | 19.12±4.72 | 16.27±6.44 | 0.038* |
Preoperative SCD (μm) | 104.62±8.70 | 105.89±16.71 | 0.731 |
1 month post operation | 140.77±10.87 | 135.74±18.18 | 0.229 |
3 months post operation | 168.54±17.94 | 161.04±18.16 | 0.137 |
6 months post operation | 176.54±16.97 | 168.78±17.64 | 0.109 |
∆SCD | 71.92±15.69 | 62.89±18.28 | 0.059 |
Preoperative SCA (μm2) | 2,904.89±706.88 | 2,775.99±559.28 | 0.464 |
1 month post operation | 3,769.57±1,059.11 | 3,691.39±957.54 | 0.779 |
3 months post operation | 5,204.56±1,180.68 | 5,003.35±817.35 | 0.473 |
6 months post operation | 5,315.58±1,078.29 | 5,055.54±803.38 | 0.323 |
∆SCA | 2,410.69±550.88 | 2,279.55±538.01 | 0.385 |
Data are presented as mean ± standard deviation. *, P<0.05, indicates statistical significance. All the postoperative parameters were significantly improved compared with the preoperative parameters (P<0.01). APACG, acute primary angle-closure glaucoma; CPACG, chronic primary angle-closure glaucoma; MAR, minimum angle of resolution; VA, visual acuity; IOP, intraocular pressure; ACD, anterior chamber depth; AOD, angle opening distance; TISA, trabecular-iris space area; TIA, trabecular-iris angle; SCD, Schlemm’s canal diameter; SCA, Schlemm’s canal area.
The ACD, AOD 500, TISA 500, and TIA 500 increased significantly after the surgery at all follow-ups in both groups (both P<0.01). The APACG group showed a greater increase in the AOD 500, TISA 500, and TIA 500 than the CPACG group (all P<0.05). However, there was no significant difference in the mean change in the ACD before and after surgery between the APACG and CPACG groups (1.63±0.31 vs. 1.50±0.29 mm, P=0.07).
The percentages of detectable SCs increased slightly after the surgery in both groups [APACG group: 74.3% (26/35) vs. 80% (28/35); CPACG group: 77.1% (27/35) vs. 82.9% (29/35); all P>0.05]. The ICC of the SC parameters measured by the same observer (H.H.) was 0.98, and that measured by different observers (H.H. and F.G.) was 0.90. According to the reference (16), ICC values <0.5 are indicative of poor reliability, values between 0.5–0.75 are indicative moderate reliability, values between 0.75–0.9 are indicative of good reliability, and values ≥0.9 are indicative of excellent reliability. Consequently, the repeatability and reproducibility of these parameters were excellent. The mean SCD and SCA increased significantly after the surgical treatment, and this increase was maintained at the last follow-up in both the APACG group (SCD: 104.62±8.70 vs. 176.54±16.97 µm; SCA: 2,904.89±706.88 vs. 5,315.58±1,078.29 µm2; all P<0.01) and the CPACG group (SCD: 105.89±16.71 vs. 168.78±17.64 µm; SCA: 2,775.99±559.28 vs. 5,055.54±803.38 µm2; all P<0.01). However, there was no significant difference in the mean increase between the APACG group and the CPACG group (P>0.05). Representative SC images obtained before and after surgery are shown in Figure 3.
Correlation analysis of the changes in the SC parameters
We analyzed the changes in the SCD and SCA from baseline to 6 months after surgery, and found that the changes in the SCD and SCA were correlated with the changes in the IOP (∆SCD: r=0.356, P=0.009; ∆SCA: r=0.347, P=0.011), AOD 500 (∆SCD: r=0.289, P=0.036; ∆SCA: r=0.281, P=0.041), and TIA 500 (∆SCD: r=0.349, P=0.010; ∆SCA: r=0.289, P=0.036). However, there was no statistically significant correlation between changes in the SC and other baseline factors, such as age, gender, right/left eye, C/D, MD, refraction, disease duration, PAS range, AL, CCT, LT, and pupil diameter. The results are set out in Table 3 and Figure 4. Further, the multiple linear regression analysis showed that only the change of IOP was associated with the SCD change (β =0.281, P=0.040) and the SCA change (β =0.295, P=0.039) (Table 4).
Table 3
Parameters | ∆SCD | ∆SCA | |||
---|---|---|---|---|---|
r | P value | r | P value | ||
APACG vs. CPACG | −0.261 | 0.059 | −0.122 | 0.385 | |
Age | 0.120 | 0.393 | −0.191 | 0.171 | |
Gender | 0.026 | 0.851 | 0.215 | 0.121 | |
Right/left eye | −0.043 | 0.761 | 0.077 | 0.581 | |
C/D | −0.081 | 0.565 | −0.091 | 0.518 | |
MD | 0.082 | 0.564 | 0.040 | 0.776 | |
Disease duration | −0.129 | 0.359 | −0.021 | 0.879 | |
PAS range | 0.239 | 0.085 | 0.024 | 0.863 | |
Refraction | −0.079 | 0.575 | 0.141 | 0.313 | |
Axial length | 0.065 | 0.643 | −0.178 | 0.202 | |
CCT | −0.027 | 0.848 | −0.052 | 0.711 | |
LT | −0.182 | 0.192 | −0.137 | 0.328 | |
logMAR VA | −0.137 | 0.328 | −0.159 | 0.257 | |
Pupil diameter | 0.173 | 0.219 | −0.047 | 0.741 | |
∆IOP | 0.356 | 0.009* | 0.347 | 0.011* | |
∆SCD | – | – | 0.402 | 0.003* | |
∆SCA | 0.402 | 0.003* | – | – | |
∆ACD | −0.060 | 0.671 | −0.059 | 0.676 | |
∆AOD 500 | 0.289 | 0.036* | 0.281 | 0.041* | |
∆TISA 500 | 0.150 | 0.285 | 0.031 | 0.828 | |
∆TIA 500 | 0.349 | 0.010* | 0.289 | 0.036* |
*, P<0.05, indicates statistical significance. SC, Schlemm’s canal; SCD, Schlemm’s canal diameter; SCA, Schlemm’s canal area; APACG, acute primary angle-closure glaucoma; CPACG, chronic primary angle-closure glaucoma; C/D, cup-to-disc ratio; MD, mean deviation; PAS, peripheral anterior synechiae; CCT, central corneal thickness; LT, lens thickness; MAR, minimum angle of resolution; VA, visual acuity; IOP, intraocular pressure; ACD, anterior chamber depth; AOD, angle opening distance; TISA, trabecular-iris space area; TIA, trabecular-iris angle.
Table 4
Parameters | ∆SCD | ∆SCA | |||
---|---|---|---|---|---|
Beta | P value | Beta | P value | ||
APACG vs. CPACG | −0.159 | 0.266 | 0.024 | 0.870 | |
Age | 0.191 | 0.173 | −0.142 | 0.331 | |
Gender | 0.031 | 0.825 | 0.241 | 0.111 | |
PAS range | 0.258 | 0.066 | −0.062 | 0.667 | |
∆IOP | 0.281 | 0.040* | 0.295 | 0.039* | |
∆AOD 500 | −0.043 | 0.824 | 0.020 | 0.920 | |
∆TIA 500 | 0.291 | 0.142 | 0.248 | 0.230 |
*, P<0.05, indicates statistical significance. SCD, Schlemm’s canal diameter; SCA, Schlemm’s canal area; APACG, acute primary angle-closure glaucoma; CPACG, chronic primary angle-closure glaucoma; PAS, peripheral anterior synechiae; IOP, intraocular pressure; AOD, angle opening distance; TIA, trabecular-iris angle.
DiscussionOther Section
In this study, SC expansion was observed after phaco-GSL in both the APACG and CPACG patients, and was maintained for at least 6 months after surgery. In addition, a significant correlation was found between the SC expansion and IOP decrease. These findings suggested that the SC provides valuable information and anatomical evidence that could be used to assess the efficacy of phaco-GSL. To our knowledge, this is the first in-depth evaluation of anatomical changes in the SC after phaco-GSL in patients with PACG using SS-OCT.
Phaco-GSL surgery was performed in this study. This surgery involves the removal of the cataract and the separation of the PAS. Lens removal can deepen the anterior chamber, eliminate pupillary obstruction, and effectively widen the ACA due to the increased thickness or a more anterior position of the lens in PACG. The separation of the PAS by GSL can restore the physiological drainage pathway. In the absence of adhesions, most of the aqueous humor can flow out through the conventional TM-SC pathway. Consequently, the postoperative IOP can be lowered after phaco-GSL. Therefore, phaco-GSL has been reported to be an effective and important surgical technique for the treatment of angle-closure glaucoma (8-10,17-20).
We found that the IOP significantly decreased in both the APACG and CPACG patients at 1 week, 1 month, 3 months, and 6 months after surgery. IOP decreased by 40% in the APACG group and by 37% in the CPACG group at the last follow-up visit. The results suggest that short-term (6 months) IOP control can be effectively achieved by phaco-GSL in both APACG and CPACG patients, which is consistent with the findings of previous research (17-20). Zhuo et al. conducted a prospective study to investigate the effects of phacoemulsification as an initial procedure to control IOP in eyes with APAC and CPACG, and found a reduction in postoperative IOP in both groups during the 6-month follow-up period (17). Tian et al. retrospectively analyzed the clinical effects of phaco-GSL in acute and chronic PAC/PACG patients and observed a decrease in IOP for at least 3 months (18). White et al. retrospectively assessed the effect of phaco-GSL in APAC and CPAC eyes for about 2 years, and reported a significant reduction in IOP in both groups (19). The present findings and previous findings confirm that combined phaco-GSL is effective in treating PACG eyes. IOP control in these glaucoma patients after surgery may be related to the anatomical change of the ACA structures.
Recently, there have been significant advancements in anterior-segment imaging technology, particularly AS-OCT, which is now widely used to non-invasively assess the anatomical structure of the ACA. The SC serves as the primary drainage system for aqueous humor outflow and plays a crucial role in influencing the aqueous humor outflow. The development of AS-OCT has enabled the visualization and assessment of the SC. The SCD ranges from 127–283 µm, and its cross-sectional SCA ranges from 4,064–13,991 µm2 in normal eyes (21,22). The percentages of detectable SCs in our patients before surgery were 74.3% and 77.1% in the APACG and CPACG groups, respectively, which is consistent with that reported (75%) in a previous study of patients with PACG (12), and is similar to that reported (78%) in patients with primary open-angle glaucoma (POAG), but is lower than that reported (86%) in normal subjects (22). Our results support the findings of previous in vivo human OCT studies (12,21,22).
After surgery, the angle width parameters (AOD 500, TIA 500, and TISA 500) were significantly increased in both groups, and there was no significant difference between the two groups; however, before surgery the APACG patients had a more crowded anterior segment than the CPACG patients. These findings support those of previous studies (23-28). The improved angle width parameters in both groups are related to the lens extraction, which may diminish the anterior position of the ciliary processes, reduce the plateau iris component of the angle closure, and flatten the iris leaf and move it posteriorly. Further, viscoelastic and saline infusion during phacoemulsification may deepen the anterior chamber (27). In addition, we found that the visibility of the SC increased slightly after surgery, but no statistically significant difference was observed. Further, the mean SCD and SCA increased significantly after surgery (P<0.05), and this increase was maintained for at least 6 months after surgery. The SC increase in our study may be due to positive flushing pressure during the phacoemulsification procedure, exposure of the TM by GSL, the widening of the ACA, the relief of the pupillary block, increased ciliary muscle contractility after cataract surgery (29), and postoperative capsule fibrosis and capsule contraction (30,31). Our results showed the expansion of the SC accompanied by a sufficiently low IOP after phaco-GSL. In addition, the multiple linear regression analysis showed that the change in IOP was only associated with the change of SCD and the change of SCA.
The relationship between the IOP and SC has received increasing attention in recent years (32-40). Various studies have used AS-OCT to visualize the microstructure of the aqueous humor outflow pathway. These studies have consistently shown that the SCA of glaucoma eyes is smaller than that of normal eyes (22,32,33). Kagemann et al. showed that a sudden increase in IOP significantly reduced SC cross-sectional area in healthy eyes (34,35). Another study conducted by Chen et al. used an ophthalmodynamometer to apply external pressure on the eyeball and observed that these pressure-induced changes in the SC appeared to directly influence the outflow facility (36). Chung et al. reported a positive association between the SCA at the baseline and the mean IOP reduction after using IOP-lowering agents in patients with POAG (37). Canaloplasty is a surgical intervention that involves viscodilating the SC to enlarge the drainage canal. Fuest et al. found that the SC increased with IOP reduction after canaloplasty in glaucoma patients (38). Similar to previous studies, we found that the change in SC size is correlated with the function of aqueous outflow. Thus, the SC provides valuable information that could be used to assess the efficacy of phaco-GSL. An enlarged SC provides strong evidence of the surgical effect and may also be an additional mechanism of IOP reduction after phaco-GSL in PACG. Further studies need to be conducted to investigate the mechanism of the SC and long-term changes in the SC.
The present study had several limitations. First, we only obtained the SC morphology for the nasal and temporal quadrants, as the images of the superior and inferior quadrants could not be obtained without manipulating the eyelid, which can compress the angle structures. Second, the sample size was relatively small, making it difficult to investigate the SC changes at different PACG stages. Third, the follow-up period was relatively short; thus, longer-term changes in the SC after surgery is still unclear. Fourth, the results of multivariate analyses may vary depending on the choice of the objective variable. Therefore, studies with larger sample sizes and further refined objective variables need to be conducted in the future.
ConclusionsOther Section
SS-OCT clearly visualized postoperative anatomical changes in the SC after phaco-GSL. SC expansion was observed after phaco-GSL in patients with PACG (both APACG and CPACG). An expansion in the SC was associated with a reduction in IOP. Thus, the SC provides anatomical evidence that could be used to assess the efficacy of phaco-GSL.
AcknowledgmentsOther Section
Funding: This work was supported by
FootnoteOther Section
Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://qims.amegroups.com/article/view/10.21037/qims-24-269/rc
Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://qims.amegroups.com/article/view/10.21037/qims-24-269/coif). The authors have no conflicts of interest to declare.
Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki (as revised in 2013) and was approved by the Ethics Committee of the Eye, Ear, Nose, and Throat Hospital of Fudan University (No. 2021078). Written informed consent was obtained from all participants.
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