Quantitative Iris Parameters and Association with Narrow Angles

doi:10.1016/j.ophtha.2009.06.017

Ophthalmology

Volume 117, Issue 1, January 2010, Pages 11-17

https://doi.org/10.1016/j.ophtha.2009.06.017 Get rights and content

Purpose

To investigate the relationship between quantitative iris parameters (iris curvature [I-Curv], iris area [I-Area], and iris thickness) and the presence of narrow angles.

Design

Cross-sectional, community-based study.

Participants

We recruited 2047 subjects >50 years old without ophthalmic symptoms from a community clinic in Singapore.

Methods

All subjects underwent gonioscopy and anterior segment optical coherence tomography (AS-OCT) under dark conditions. An eye was considered to have narrow angles if the posterior pigmented trabecular meshwork was not visible for ≥180° on nonindentation gonioscopy with the eye in the primary position. Customized software was used on horizontal AS-OCT scans to measure I-Curv, I-Area, and iris thickness 750 μm (IT750) and 2000 μm (IT2000) from the scleral spur. The average of both temporal and nasal measured values of the right eye was used for analysis.

Main Outcome Measures

The association between iris parameters and narrow angles on gonioscopy.

Results

Iris parameters from 1465 eyes (71.6%) were available for analysis. Of these, 315 subjects (21.5%) had narrow angles. The mean I-Curv (0.366 vs 0.259 mm; P<0.020), IT750 (0.476 vs 0.453 mm; P<0.001), and IT2000 (0.491 vs 0.482 mm; P = 0.010) were greater in persons with than without narrow angles. After adjusting for age, gender, anterior chamber depth, axial length, and pupil size, the greater I-Curv, I-Area, IT750, and IT2000 were significantly associated with narrow angles (odds ratio [OR] 2.5 and 95% confidence interval [CI], 1.3–5.1; OR, 2.7 and 95% CI, 1.6–4.8; OR, 2.6 and 95% CI, 1.6–4.1; OR, 2.7 and 95% CI, 1.5–4.7, comparing 4th with 1st quartile for each parameter, respectively). In stratified analysis, women and subjects aged ≥60 years had stronger associations for most iris parameters with narrow angles than men and younger subjects.

Conclusions

Quantitative iris parameters (I-Curv, I-Area, and iris thickness) are independently associated with narrow angles, particularly in women and older subjects. These data provide further insights into the pathogenesis of angle closure in Singaporeans.

Financial Disclosure(s)

Proprietary or commercial disclosure may be found after the references.

Section snippets

Methods

This cross-sectional study included persons aged ≥50 years who were recruited between December 2005 and July 2006 from a government-run polyclinic that provides primary health care services for residents living in the area around the clinic. Details of the study have been described previously.12, 18 In brief, subjects were participants of a study evaluating new screening instruments for narrow angles and did not have any ophthalmic complaints at the time of consultation. Subjects were

Results

A total of 2047 participants were recruited into the study. Among them, 582 subjects were excluded for the following reasons: 11 subjects could not undergo gonioscopy; 62 subjects could not complete AS-OCT examination or had poor quality AS-OCT images; 42 subjects had software delineation errors; and the scleral spur was not clearly visible on AS-OCT images in 467 subjects. Therefore, data from 1465 participants (71.6%) were available and included in the analysis. Of these, 793 (54.1%) were

Discussion

This study assessed the relationship between quantitatively measured iris parameters and presence of narrow angles in a large, community-based population. We found that greater I-Curv, I-Area and iris thickness were independently associated with narrow angles, after adjusting for other known associated biometric parameters. These represent novel associations identified for the condition.

The association of greater I-Curv with narrow angles shows that there was more anterior bulging of the iris

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Cited by (172)

Performance of anterior segment OCT-based algorithms in the opportunistic screening for primary angle-closure disease
2024, Heliyon
This study aimed to investigate the performance of deep learning algorithms in the opportunistic screening for primary angle-closure disease (PACD) using combined anterior segment parameters.
This was an observational, cross-sectional hospital-based study. Patients with PACD and healthy controls who underwent comprehensive eye examinations, including gonioscopy and anterior segment optical coherence tomography (ASOCT) examinations under both light and dark conditions, were consecutively enrolled from the Department of Ophthalmology at the Beijing Tongren Hospital between November 2020 and June 2022. The anterior chamber, anterior chamber angle, iris, and lens parameters were assessed using ASOCT. To build the prediction models, backward logistic regression was utilized to select the variables to discriminate patients with PACD from normal participants, and the area under the receiver operating characteristic curve was used to evaluate the efficacy of the opportunistic screening.
The data from 199 patients (199 eyes) were included in the final analysis and divided into two groups: PACD (109 eyes) and controls (90 eyes). Angle opening distance at 500 μm, anterior chamber area, and iris curvature measured in the light condition were included in the final prediction models. The area under the receiver operating characteristic curve was 0.968, with a sensitivity of 91.74 % and a specificity of 91.11 %.
ASOCT-based algorithms showed excellent diagnostic performance in the opportunistic screening for PACD. These results provide a promising basis for future research on the development of an angle-closure probability scoring system for PACD screening.
Progressive Changes in the Anterior Segment and Their Impact on the Anterior Chamber Angle in Primary Angle Closure Disease
2024, American Journal of Ophthalmology
To investigate longitudinal changes in the anterior segment (AS) using serial optical coherence tomography (OCT) images and determine the impact of these changes on the anterior chamber angle (ACA) in eyes with primary angle closure disease (PACD) treated with laser peripheral iridotomy (LPI).
Retrospective clinical cohort study.
This study included 103 patients with PACD who underwent LPI and were followed up by a mean 6.7 ± 1.7 AS-OCT examinations for a mean 6.5 ± 2.9 years. Temporal changes in AS-OCT parameters, including anterior chamber depth (ACD), angle opening distance (AOD750), angle recess area (ARA750), iris thickness (IT750), lens vault (LV), and pupil diameter (PD), were analyzed by multivariate linear mixed effects models (LMEMs).
Multivariate LMEMs showed that decrease in AOD750 was not significant (–1.59 µm/y, P = .222); however, ARA750 decreased over time (–2.3 × 10³ µm²/y, P = .033) and SSA showed marginal significance (–0.20°/y, P = .098), and LV increased significantly (11.6 µm/y, P < .001) after LPI. Mean LV change was negatively associated with AOD750, ARA750, and SSA, whereas PD was negatively associated with ARA750 (P < .001 each). PD decreased with aging (–13.7 µm/y, P = .036), accompanied by thinning of IT750 (–1.7 µm/y, P = .063).
LV tends to increase with aging, which contributes to the shallowing of the anterior chamber and narrowing of ACA in PACD eyes treated with LPI. In the meantime, pupillary constriction and subsequent peripheral iris thinning associated with aging could possibly offset the effect of ACA narrowing.
Anterior segment measurements and determinants of angle width with short, medium, and long axial lengths in a rural Chinese population
2023, Heliyon
To report the anterior segment measurements and investigate the determinants of angle width with short, medium, and long axial length (AL) in a rural Chinese population.
Observational, population-based, cross-sectional study.
Subjects aged ≥35 years who underwent complete ocular examinations during the follow-up of the Handan Eye Study were included. Ocular data of the right eye were analyzed. Anterior segment parameters were obtained and stratified by age and sex. AL was categorized into short (<22.0 mm), medium (22.0–23.5 mm), and long (>23.5 mm) subgroups. Linear regression analyses were performed to identify the parameters associated with angle width (angle opening distance at 500 μm from the scleral spur (SS) [AOD500]).
The final analysis included 4435 subjects (58.0 [49.0, 64.0] years old, 44.1% males). Smaller AOD500 was significantly associated with female sex (P = 0.032), larger iris thickness at 750 μm from the SS (IT750) (P < 0.001), larger lens vault (LV) (P < 0.001), and smaller anterior chamber volume (ACV) (P < 0.001) in the short AL subgroup; larger sphere equivalent (SE), IT750, iris curvature (IC), and LV and smaller ACV (all P < 0.001) in the medium AL subgroup; and larger SE, IT750, IA, IC, and LV and smaller ACV (all P < 0.001) in the long AL subgroup.
Our study provides the anterior segment parameters of a large rural Chinese population. IT750, ACV, and LV were found to be the most important factors associated with angle width.
Ocular Biometric Risk Factors for Progression of Primary Angle Closure Disease: The Zhongshan Angle Closure Prevention Trial
2022, Ophthalmology
To assess baseline ocular biometric risk factors for progression from primary angle closure suspect (PACS) to primary angle closure (PAC) or acute angle closure (AAC).
Prospective, observational study.
Six hundred forty-three mainland Chinese with untreated PACS.
Participants underwent baseline clinical examinations, including gonioscopy, anterior segment OCT (AS-OCT) imaging, and A-scan ultrasound biometry as part of the Zhongshan Angle Closure Prevention (ZAP) Trial. Primary angle closure suspect was defined as an inability to visualize pigmented trabecular meshwork in 2 or more quadrants based on static gonioscopy. Primary angle closure was defined as development of intraocular pressure above 24 mmHg or peripheral anterior synechiae. Progression was defined as development of PAC or an AAC attack. Multivariable logistic regression models were developed to assess biometric risk factors for progression.
Six-year progression from PACS to PAC or AAC.
Six hundred forty-three untreated eyes (609 nonprogressors, 34 progressors) of 643 participants were analyzed. In a multivariable model with continuous parameters, narrower horizontal angle opening distance of 500 μm from the scleral spur (AOD₅₀₀; odds ratio [OR], 1.10 per 0.01-mm decrease; P = 0.03), flatter horizontal iris curvature (IC; OR, 1.96 per 0.1-mm decrease; P = 0.01), and older age (OR, 1.11 per 1-year increase; P = 0.01) at baseline were associated significantly with progression (area under the receiver operating characteristic curve [AUC], 0.73). Smaller cumulative gonioscopy score was not associated with progression (OR, 1.03 per 1-modified Shaffer grade decrease; P = 0.85) when replacing horizontal AOD₅₀₀ in the multivariable model. In a separate multivariable model with categorical parameters, participants in the lowest quartile of horizontal AOD₅₀₀ (OR, 3.10; P = 0.002) and IC (OR, 2.48; P = 0.014) measurements and 59 years of age or older (OR, 2.68; P = 0.01) at baseline showed higher odds of progression (AUC, 0.72).
Ocular biometric measurements can help to risk-stratify patients with early angle closure for more severe disease. Anterior segment OCT measurements of biometric parameters describing the angle and iris are predictive of progression from PACS to PAC or AAC, whereas gonioscopy grades are not.
The Heritability of Primary Angle Closure Anatomic Traits and Predictors of Angle Closure in South Indian Siblings
2021, American Journal of Ophthalmology
To estimate the heritability of ocular biometric and anterior chamber morphologic parameters and to determine predictors of angle closure concordance in South Indian probands with angle closure and their siblings
Prospective observational cohort study
Subjects received a standardized ophthalmic examination, A-scan ultrasonography, pachymetry, and anterior segment optical coherence tomography (ASOCT) imaging. Heritability was calculated using residual correlation coefficients adjusted for age, sex, and home setting. Concordant sibling pairs were defined as both proband and sibling with angle closure. Predictors of angle closure concordance among siblings were calculated using multivariable logistic regression models.
A total of 345 sibling pairs participated. All anterior chamber parameters were highly heritable (P < .001 for all). Similarly, all iris parameters, axial length, lens thickness (LT), central corneal thickness, anterior lens curvature, lens vault (LV), spherical equivalent, and intraocular pressure were moderately to highly heritable (P < .004 for all). LV and LT were more heritable among concordant siblings (P < .05 for both). In contrast, ASOCT angle parameters had statistically insignificant heritability estimates. In multivariable analyses, siblings older than their probands were more likely to be concordant for angle closure (OR 1.05, 95% CI 1.01, 1.09; P = .02) and siblings with deeper anterior chamber depths (ACDs) compared to their proband were less likely to be concordant for angle closure (OR 0.74, 95% CI 0.64, 0.86; P < .001).
Iris, anterior chamber, and lens parameters may be heritable whereas angle parameters were not. LT and LV may play important roles in the pathogenesis of angle closure. Siblings who are older or have a shallower ACD may need more careful disease monitoring.
Differences in Ocular Biometric Measurements among Subtypes of Primary Angle Closure Disease: The Chinese American Eye Study
2021, Ophthalmology Glaucoma
To assess differences in ocular biometric measurements between primary angle closure suspect (PACS) eyes and primary angle closure (PAC) and primary angle closure glaucoma (PACG) eyes.
Cross-sectional study.
Patients with primary angle closure disease (PACD) were identified from the Chinese American Eye Study, a population-based study in Los Angeles, California.
Patients previously underwent complete ocular examinations including gonioscopy and anterior segment (AS)-OCT imaging with the Tomey CASIA SS-1000 (Tomey Corporation). Four AS-OCT images were analyzed per eye. Averaged and sectoral measurements of biometric parameters, including angle recess area (ARA), trabecular iris space area (TISA), iris area, iris curvature, lens vault, anterior chamber depth, and anterior chamber area, were compared between early PACD (PACS) and late PACD (PAC and PACG) groups. Machine learning classifiers that attempt to differentiate between early and late PACD eyes were developed by applying different regression algorithms to a training dataset of sectoral parameter measurements. Classifier performance was assessed using an independent test dataset.
Averaged and sectoral measurements of biometric parameters.
Two hundred ninety-eight eyes (231 PACS, 67 PAC or PACG) of 298 patients were analyzed. No difference was found in averaged biometric measurements between the 2 groups before (P > 0.09) or after (P > 0.14) adjusting for age and gender. Differences (P < 0.04) between the 2 groups were found for 11 sectoral parameter measurements, including ARA and TISA. The performance of machine learning classifiers developed using sectoral parameter measurements was poor on the independent test dataset for all regression algorithms (area under the receiver operating characteristic curve, 0.529–0.628).
Differences in biometric measurements between subtypes of PACD eyes were small in a population-based cohort of Chinese Americans. The poor performance of classifiers based on these measurements highlights potential challenges of developing quantitative methods to detect late PACD.

View all citing articles on Scopus

: Manuscript no. 2009-266.

: Financial Disclosure(s): Tin Aung – funding, travel support, honoraria – Carl Zeiss Meditec David S. Friedman – instrument loan – Carl Zeiss Meditec.

: Supported by grants from Singhealth, Singapore and National Medical Research Council, Singapore.

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Original articleQuantitative Iris Parameters and Association with Narrow Angles

Purpose

Design

Participants

Methods

Main Outcome Measures

Results

Conclusions

Financial Disclosure(s)

Section snippets

Methods

Results

Discussion

Surv Ophthalmol

Ophthalmology

Ophthalmology

Am J Ophthalmol

Am J Ophthalmol

Am J Ophthalmol

Am J Ophthalmol

An epidemiological study of glaucoma in Shunyi County, Beijing

Zhonghua Yan Ke Za Zhi

Glaucoma in China: how big is the problem?

Br J Ophthalmol

Glaucoma in Mongolia: a population-based survey in Hovsgol province, northern Mongolia

Arch Ophthalmol

Glaucoma in China (and worldwide): changes in established thinking will decrease preventable blindness

Br J Ophthalmol

Aetiology of the anatomical basis for primary angle closure glaucoma: biometrical comparisons between normal eyes and eyes with primary angle-closure glaucoma

Br J Ophthalmol

Ocular parameters in subgroups of angle closure glaucoma

Clin Experiment Ophthalmol

Ocular biometry in occludable angles and angle closure glaucoma: a population based survey

Br J Ophthalmol

Original article
Quantitative Iris Parameters and Association with Narrow Angles