Glaucoma is the leading cause of irreversible blindness worldwide, with an estimated 112 million people projected to be affected by 2040.1,2 Primary angle-closure glaucoma (PACG) accounts for a disproportionate share of this burden, particularly in Asian populations, where anatomical predispositions - including shallow anterior chambers, shorter axial lengths, and greater lens vault- are prevalent. India contributes significantly to this global burden, with over 11 million people above the age of 40 affected by glaucoma.3,4 PACG results from obstruction of aqueous outflow due to closure of the anterior chamber angle, leading to elevated intraocular pressure (IOP) and progressive optic nerve damage. Despite carrying a three-fold higher risk of blindness compared to primary open-angle glaucoma (POAG), PACG often follows an asymptomatic course until significant structural damage has occurred.5,6 Early and accurate identification of eyes with occludable angles is therefore essential to prevent avoidable blindness. Gonioscopy remains the clinical gold standard for anterior chamber angle assessment, providing direct visualisation of angle structures and enabling dynamic evaluation through indentation. However, its performance is examiner-dependent, contact-based, and limited in large-scale screening settings.7,8 Anterior segment optical coherence tomography (AS-OCT) has emerged as a non-contact, objective imaging modality capable of quantitative assessment of angle anatomy, including measurement of the angle opening distance (AOD500). Multiple studies have reported fair to moderate agreement between gonioscopy and AS-OCT, with AS-OCT often detecting a higher proportion of narrow or occludable angles in specific quadrants.9,10,11 The majority of comparative studies have been conducted in East Asian or Western populations. Data from North India - particularly from Rajasthan, where PACG burden is high and advanced imaging access is limited - remain sparse. The present study was undertaken to compare the quadrant-wise detection of angle closure by gonioscopy and AS-OCT in a tertiary care cohort in Jaipur, with the aim of defining the roles of both modalities in clinical practice.

This was a hospital-based, observational, cross-sectional study conducted over 18 months (May 2024 to October 2025) in a tertiary centre in Rajasthan, North India. The study was approved by the Institutional Ethics Committee (Ref: /MGMC&H/IEC/JPR/2024/1990) and was conducted in accordance with the tenets of the Declaration of Helsinki. Written informed consent was obtained from all participants prior to enrolment. Patients attending the ophthalmology outpatient department with suspected angle closure (shallow anterior chamber through Van Herick grading on slit-lamp examination), aged 40-70 years of either sex, were consecutively enrolled until the target sample size was reached. No formal eligibility screening log was maintained, all eligible patients who presented during the study period were invited to participate, and those who provided informed consent and met all inclusion criteria were enrolled. Patients who did not meet inclusion criteria or declined consent were excluded. A sample size of 50 patients was calculated using single proportion estimation, based on a PACG prevalence of approximately 2.5% in the Indian population.4 Eligible patients were required to provide voluntary written informed consent, have suspected angle closure on slit-lamp Van Herick grading, be aged 40–70 years, and be of either sex. Patients were excluded if they had known open-angle glaucoma, secondary glaucoma, or congenital glaucoma; lens-induced or post-surgical angle closure; aphakia or pseudophakia; corneal opacities precluding angle visualisation; ptosis or eyelid abnormalities precluding slit-lamp examination; prior ocular surgery or laser procedures; history of ocular trauma; systemic conditions precluding slit-lamp positioning; or inability to cooperate with examination. All patients underwent best-corrected visual acuity assessment (Snellen chart), IOP measurement (Goldmann applanation tonometry), slit-lamp biomicroscopy with Van Herick grading, gonioscopy, and AS-OCT. Optic disc evaluation was performed with a +90D lens without pharmacological dilation to avoid precipitating angle closure. Van Herick grading was performed by directing a narrow slit beam at the temporal corneal limbus (approximately 60° off-axis) and comparing peripheral anterior chamber depth with corneal thickness. Grade 1 indicates depth ≤25% corneal thickness (high risk); Grade 2 indicates depth 25–50% corneal thickness (moderate risk). Gonioscopy was performed using a three-mirror Goldmann universal diagnostic lens under low ambient illumination following topical anaesthesia and coupling medium application. All four quadrants (superior, inferior, nasal, and temporal) were assessed by a single examiner. Angle grading used the Shaffer classification system. A quadrant was defined as closed if two or fewer angle structures were visible (Shaffer Grade ≤2). To minimise examiner bias, all gonioscopic assessments were performed by a single trained examiner under standardised low-illumination conditions; AS-OCT was performed under darkroom conditions without dilation in all cases. The gonioscopy examiner and the AS-OCT grader were each masked to the other modality’s findings at the time of grading, so that quadrant-wise classification on one modality did not influence assessment on the other.7 AS-OCT was performed using the Carl Zeiss Cirrus HD-OCT Model 500 under standardised darkroom conditions without pharmacological dilation to preserve physiological angle configuration. High-resolution cross-sectional scans were obtained for each quadrant. The angle opening distance at 500 µm from the scleral spur (AOD500) was measured. A quadrant was defined as closed if AOD500 <191 µm.10,11,12 Statistical analysis Data were entered in Microsoft Excel and analysed using IBM SPSS Statistics (version 26.0). Descriptive statistics were used for demographic and clinical variables; categorical variables were expressed as frequencies and percentages. Quadrant-wise comparison of angle closure detection between gonioscopy and AS-OCT was performed using the chi-square test (or Fisher’s exact test where cell counts were <5). A p-value <0.05 was considered statistically significant. All tests were two-tailed. No subgroup or interaction analyses were pre-specified. There were no missing data; all 62 enrolled eyes had complete gonioscopy and AS-OCT data. No sensitivity analyses were performed.

Fifty patients (62 affected eyes) were included. Mean age was 56.64 ± 8.88 years (range 40-70 years); the 51–60-year age group was the largest (46%, n = 23). Females predominated (64%, n = 32). A positive family history of glaucoma in a first-degree relative was reported by 12% (n = 6) of participants. Unilateral involvement was present in 76% (n = 38) and bilateral in 24% (n = 12). Demographic data are summarised in Table 1. Visual acuity of 6/12-6/18 was the most common finding (41.9% of eyes, n = 26), followed by 6/24-6/36 (29.0%, n = 18). Near-normal vision (6/6-6/9) was present in 21.0% (n = 13) and severe impairment (≤6/60) in 8.1% (n = 5). IOP was 10-20 mmHg in 3.2% (n = 2) of eyes, 20-30 mmHg in 51.6% (n = 32), 30-40 mmHg in 37.1% (n = 23), and ≥40 mmHg in 8.1% (n = 5). Grade 2 (anterior chamber depth 25-50% of corneal thickness) was the most common finding (56.5%, n = 35 eyes), followed by Grade 1 (≤25% corneal thickness; 43.5%, n = 27 eyes), indicating predominantly shallow to moderately shallow anterior chambers across the cohort. Gonioscopy identified angle closure most frequently in the superior quadrant (50.0%, n = 31 of 62 eyes), followed by the inferior (24.2%, n = 15) and nasal (24.2%, n = 15) quadrants. The temporal quadrant was least frequently involved (16.1%, n = 10). AS-OCT identified angle closure most frequently in the nasal quadrant (45.2%, n = 28 of 62 eyes), followed by the superior (40.3%, n = 25) and inferior (40.3%, n = 25) quadrants. Temporal involvement was least common (17.7%, n = 11). This distribution differed from the gonioscopic pattern, with relatively greater detection in the nasal and inferior quadrants. The overall quadrant-wise distribution of angle closure differed significantly between gonioscopy and AS-OCT (p = 0.013). Quadrant-wise analysis showed that detection in the nasal quadrant was significantly higher on AS-OCT than gonioscopy (45.2% vs. 24.2%; difference +21.0%, 95% CI 4.6-37.3%; χ² = 6.02, p = 0.014). Differences in the inferior quadrant approached but did not reach significance (40.3% AS-OCT vs. 24.2% gonioscopy; difference +16.1%, 95% CI -0.1-32.3%; χ² = 3.69, p = 0.055). Superior and temporal quadrant detection did not differ significantly between modalities. Detailed quadrant-wise comparisons are presented in Table 2 and illustrated in Figure 1. Table 1. Demographic characteristics of study participants (n = 50). Variable Category n (%) Details Age group (years) n = 50 Mean 56.64 ± 8.88 years; range 40–70 40–50 15 (30%) 51–60 23 (46%) Largest age group 61–70 12 (24%) Sex Female 32 (64%) Male 18 (36%) Family history of glaucoma 6 (12%) First-degree relative Eye involvement Total: 62 affected eyes Unilateral 38 (76%) Bilateral 12 (24%) Table 2. Quadrant-wise angle closure detection by gonioscopy and AS-OCT (n = 62 eyes) Quadrant Gonioscopy AS-OCT Difference (95% CI) χ² p Closed n (%) Open n (%) Closed n (%) Open n (%) Superior 31 (50.0%) 31 (50.0%) 25 (40.3%) 37 (59.7%) -9.7% (-27.1 to 7.7%) 1.17 0.280 Inferior 15 (24.2%) 47 (75.8%) 25 (40.3%) 37 (59.7%) +16.1% (-0.1 to 32.3%) 3.69 0.055 Nasal 15 (24.2%) 47 (75.8%) 28 (45.2%) 34 (54.8%) +21.0% (4.6 to 37.3%) 6.02 0.014* Temporal 10 (16.1%) 52 (83.9%) 11 (17.7%) 51 (82.3%) +1.6% (-11.6 to 14.8%) 0.06 0.810 Overall distribution – 0.013* Comparisons performed using chi-square test. Percentages represent proportion of 62 eyes with angle closure per quadrant. Difference = AS-OCT minus gonioscopy (percentage points). AS-OCT = anterior segment optical coherence tomography; CI = confidence interval; χ² = chi-square statistic. *p < 0.050. Figure 1. Quadrant-wise comparison of angle closure detection rates by gonioscopy and AS-OCT (n = 62 eyes). Grouped bars show the percentage of the 62 study eyes with angle closure detected in each quadrant, by modality. The asterisk denotes a statistically significant between-modality difference (nasal quadrant, p = 0.014); corresponding numerical values, confidence intervals, and χ² statistics for all quadrants are presented in Table 2. AS-OCT = anterior segment optical coherence tomography.

This hospital-based cross-sectional study compared gonioscopy and AS-OCT for quadrant-wise detection of angle closure in a tertiary care cohort in Rajasthan, North India. The divergent quadrant-wise pattern observed between the two modalities corroborates established evidence that gonioscopy and AS-OCT are complementary rather than interchangeable diagnostic tools, each capturing a partly distinct facet of angle anatomy rather than one simply outperforming the other. The demographic profile of the study cohort - female predominance (64%), mean age in the sixth decade, and a proportion with positive family history (12%) - is consistent with the known epidemiological characteristics of PACG in Asian populations.2,5,6 Female sex is well recognised as a risk factor for angle-closure disease, attributed to anatomical differences including shallower anterior chambers and shorter axial lengths.6 The predominance of superior quadrant closure on gonioscopy is consistent with published literature. Superior angle narrowing has been attributed to a combination of gravitational, morphological, and iris-crowding factors that render the superior angle most susceptible to appositional closure.7 This quadrant is also most amenable to dynamic gonioscopic evaluation, which may further contribute to its higher detection rate with this modality. In contrast, AS-OCT detected significantly more nasal quadrant closure than gonioscopy, with a similar but non-significant trend in the inferior quadrant. This pattern is consistent with prior comparative studies. Sakata et al. reported that AS-OCT detected more closed angles than gonioscopy, particularly in quadrants where closure was appositional rather than synechial.10 Desmond et al., in a systematic review and meta-analysis of 23 studies, confirmed that AS-OCT demonstrates high sensitivity (pooled median 87%) for angle closure detection, though modality-specific quadrant-wise distributions may differ from those of gonioscopy.13 The non-contact, standardised darkroom conditions of AS-OCT likely preserve physiological angle configuration more faithfully than gonioscopy, which is susceptible to examiner-induced inadvertent indentation - particularly in the inferior and nasal quadrants.8 Recent Indian and Asian studies support these findings. Jaseena and Rekha (2022) found statistically significant discrepancies between gonioscopy and AS-OCT in quadrant-wise detection, with AS-OCT detecting more closures in non-superior quadrants.14 Similarly, Imran et al. (2023) reported higher AS-OCT detection in non-superior quadrants relative to gonioscopy.15 Radhakrishnan et al. demonstrated that anterior segment OCT provides an objective and reproducible method of angle assessment with good agreement with gonioscopic findings, supporting its role as an adjunct rather than a replacement for gonioscopy.16 Shruthi et al. (2025), in a recent quadrant-wise study from India, similarly reported complementary detection patterns between the two modalities.17 The present study extends these findings to a North Indian population in Rajasthan, where comparative angle assessment data have been limited. The statistically significant overall difference between modalities should not be interpreted as evidence of superiority of one over the other. Rather, it reflects modality-specific anatomical detection patterns. Gonioscopy provides unique dynamic assessment capabilities- including detection of peripheral anterior synechiae and differentiation of appositional from synechial closure - capabilities that AS-OCT cannot replicate.7,8 AS-OCT, in turn, provides objective, reproducible, non-contact documentation that is particularly valuable for screening, follow-up, and tele-triage settings where contact-based assessment may not be feasible.13,18 The clinical implication is that gonioscopy and AS-OCT are best viewed as complementary rather than competing tools: gonioscopy remains essential for dynamic decision-making and detection of synechial closure, while AS-OCT’s objectivity and reproducibility make it particularly suited to flagging subtle inferior and nasal angle narrowing that may otherwise be under-recognised on dynamic examination alone. This study has several limitations. It was conducted at a single tertiary care centre, which may limit generalisability to community-based or rural populations. The sample size of 50 patients (62 eyes), while sufficient to demonstrate statistically significant quadrant-wise differences, is modest. All gonioscopy was performed by a single examiner, precluding assessment of inter-observer variability. The cross-sectional design does not permit evaluation of disease progression or longitudinal agreement between modalities. Kappa statistics for inter-modality agreement were not calculated, which would have provided a more complete assessment of concordance. Additionally, the AOD500 threshold of 191 µm used to define closure on AS-OCT, while based on published normative data, may not be universally applicable across all populations.

Gonioscopy and AS-OCT demonstrate complementary but non-identical quadrant-wise detection patterns in angle-closure disease, and neither modality alone captures the full spectrum of angle-closure pathology. Gonioscopy remains the clinical gold standard for dynamic angle assessment, while AS-OCT offers an objective, non-contact adjunct that is particularly informative in quadrants prone to examiner-induced indentation artefact. A combined approach - gonioscopy for dynamic clinical decision-making and AS-OCT for objective documentation, screening, and follow-up, may offer the most comprehensive evaluation of angle-closure glaucoma in clinical practice. Conflicts of interest The authors declare no conflicts of interest. Source of Funding This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sector. Acknowledgements Not Applicable.

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