Limbal Anterior Chamber Depth Research Articles

An education-based intervention investigating the accuracy of community-based optometrists evaluating limbal anterior chamber depth.

In the UK, referrals for suspected primary angle closure (PAC) by community-based optometrists (CBO) to the hospital eye service show moderate accuracy. This study aimed to assess the interobserver agreement of limbal anterior chamber depth (LACD) between CBOs and ophthalmologists and evaluate the impact of an education intervention. Using a 7-point LACD grading scale, consultant ophthalmologists graded an LACD image dataset developed from 100 patients attending Moorfields Eye Hospital. Two sets of 84 images were utilised for two LACD online assessments. CBO were recruited and undertook assessments before and after a PAC education package (EP) between August 2023 and January 2024. Fifty-two optometrists completed the initial LACD assessment with a median of 19.0 (IQR 9.3-24.8) years post-registration experience. Using the 7-point LACD grading scale, mean weighted kappa (Kw) for pre-EP was moderate, 0.42 (95% CI, 0.36-0.48), increasing to 0.47 (0.42-0.53) post-EP. Conversion to the 4-point grading scale, Kw was substantial, pre-EP 0.61, (0.56-0.66) and post-EP Kw 0.64 (0.58-0.69). An LACD threshold (<25%) sensitivity and specificity pre-EP was 86.0% (79.9-91.3%) and 84.6 (82.3-86.9), respectively. Post-EP sensitivity decreased to 78.2% (74.1-85.1%) (p = 0.049) but specificity increased to 90.4 (88.1-92.8) (p < 0.001). The 4-point LACD grading scale would be more applicable for a case-finding setting. An accessible EP improved agreement and specificity using the joint Royal College of Ophthalmologists/College of Optometrists PAC referral threshold. This EP may reduce false positive PAC referrals and could be rapidly disseminated to CBO. Further research is needed to assess real-world PAC referrals after an education intervention.

Technologies for the diagnosis of angle closure glaucoma (ACE): protocol of a prospective, multicentre, cross-sectional diagnostic study

IntroductionAngle-closure is responsible for half of all glaucoma blindness globally. Patients with suspected glaucoma require assessment of the drainage angle by an experienced clinician. The goal of this study is...

Fourteen-Year Outcome of Angle-Closure Prevention with Laser Iridotomy in the Zhongshan Angle-Closure Prevention Study: Extended Follow-up of a Randomized Controlled Trial

This study aimed to evaluate the efficacy of laser peripheral iridotomy (LPI) prophylaxis for patients with primary angle-closure suspect (PACS) after 14 years and to identify risk factors for the conversion from PACS to primary angle closure (PAC). Extended follow-up of the Zhongshan Angle-Closure Prevention Study. Eight hundred eighty-nine Chinese patients 50 to 70 years of age with bilateral PACS. Each patient received LPI in 1 randomly selected eye, with the fellow untreated eye serving as a control. Because the risk of glaucoma was low and acute angle closure (AAC) occurred only rarely, the follow-up was extended to 14 years despite substantial benefits of LPI reported after the 6-year visit. Incidence of PAC, a composite end point including peripheral anterior synechiae, intraocular pressure (IOP) of > 24 mmHg, or AAC. During the 14 years, 390 LPI-treated eyes and 388 control eyes were lost to follow-up. A total of 33 LPI-treated eyes and 105 control eyes reached primary end points (P < 0.01). Within them, 1 LPI-treated eye and 5 control eyes progressed to AAC. Primary angle-closure glaucoma was found in 2 LPI-treated eyes and 4 control eyes. The hazard ratio for progression to PAC was 0.31 (95% confidence interval, 0.21-0.46) in LPI-treated eyes compared with control eyes. At the 14-year visit, LPI-treated eyes showed more severe nuclear cataract, higher IOP, and larger angle width and limbal anterior chamber depth (LACD) than control eyes. Higher IOP, shallower LACD, and greater central anterior chamber depth (CACD) were associated with an increased risk of end points developing in control eyes. In the treated group, eyes with higher IOP, shallower LACD, or less IOP elevation after the darkroom prone provocative test (DRPPT) were more likely to demonstrate PAC after LPI. Despite a two-third decrease in PAC occurrence after LPI, the cumulative risk of progression was relatively low in the community-based PACS population over 14 years. Apart from IOP, IOP elevation after DRPPT, CACD, and LACD, more risk factors are needed to achieve precise prediction of PAC occurrence and to guide clinical practice. The author(s) have no proprietary or commercial interest in any materials discussed in this article.

How accurate is limbal anterior chamber depth (LACD) for the diagnosis of primary angle closure glaucoma?

How accurate is limbal anterior chamber depth (LACD) for the diagnosis of primary angle closure glaucoma?

Screening for angle-closure disease in the community: A review

Primary angle-closure glaucoma (PACG) has a higher risk of association with blindness compared to primary open-angle glaucoma. Early determination of PAC disease (PACD) before progression to PACG can help prevent loss of vision. Although gonioscopy is the gold standard for the determination of angle status, it requires more training and experience and may not be feasible to use for screening. We reviewed the performance of other modalities of angle assessment in population studies in comparison with gonioscopy. Assessment of limbal anterior chamber depth, biometric parameters such as central anterior chamber depth, lens thickness, axial length measurements, and anterior segment optical coherence tomography were used to qualitatively and quantitatively assess the angle structures in these studies. The sensitivity, specificity, and predictive values varied widely due to the use of varying techniques and definitions. A combination of more than 1 parameter was found to give better results in comparison with gonioscopy in some studies. Individual or combination tests most appropriate for screening need to be determined and reassessed by further well-controlled studies with uniform criteria.

Non-contact tests for identifying people at risk of primary angle closure glaucoma.

Primary angle closure glaucoma (PACG) accounts for 50% of glaucoma blindness worldwide. More than three-quarters of individuals with PACG reside in Asia. In these populations, PACG often develops insidiously leading to chronically raised intraocular pressure and optic nerve damage, which is often asymptomatic. Non-contact tests to identify people at risk of angle closure are relatively quick and can be carried out by appropriately trained healthcare professionals or technicians as a triage test. If the test is positive, the person will be referred for further specialist assessment. To determine the diagnostic accuracy of non-contact tests (limbal anterior chamber depth (LACD) (van Herick test); oblique flashlight test; scanning peripheral anterior chamber depth analyser (SPAC), Scheimpflug photography; anterior segment optical coherence tomography (AS-OCT), for identifying people with an occludable angle. We searched the following bibliographic databases 3 October 2019: CENTRAL; MEDLINE; Embase; BIOSIS; OpenGrey; ARIF and clinical trials registries. The searches were limited to remove case reports. There were no date or language restrictions in the searches. We included prospective and retrospective cross-sectional, cohort and case-control studies conducted in any setting that evaluated the accuracy of one or more index tests for identifying people with an occludable angle compared to a gonioscopic reference standard. Two review authors independently performed data extraction and quality assessment using QUADAS2 for each study. For each test, 2 x 2 tables were constructed and sensitivity and specificity were calculated. When four or more studies provided data at fixed thresholds for each test, we fitted a bivariate model using the METADAS macro in SAS to calculate pooled point estimates for sensitivity and specificity. For comparisons between index tests and subgroups, we performed a likelihood ratio test comparing the model with and without the covariate. We included 47 studies involving 26,151 participants and analysing data from 23,440. Most studies were conducted in Asia (36, 76.6%). Twenty-seven studies assessed AS-OCT (analysing 15,580 participants), 17 studies LACD (7385 participants), nine studies Scheimpflug photography (1616 participants), six studies SPAC (5239 participants) and five studies evaluated the oblique flashlight test (998 participants). Regarding study quality, 36 of the included studies (76.6%) were judged to have a high risk of bias in at least one domain.The use of a case-control design (13 studies) or inappropriate exclusions (6 studies) raised patient selection concerns in 40.4% of studies and concerns in the index test domain in 59.6% of studies were due to lack of masking or post-hoc determination of optimal thresholds. Among studies that did not use a case-control design, 16 studies (20,599 participants) were conducted in a primary care/community setting and 18 studies (2590 participants) in secondary care settings, of which 15 investigated LACD. Summary estimates were calculated for commonly reported parameters and thresholds for each test; LACD ≤ 25% (16 studies, 7540 eyes): sensitivity 0.83 (95% confidence interval (CI) 0.74, 0.90), specificity 0.88 (95% CI 0.84, 0.92) (moderate-certainty); flashlight (grade1) (5 studies, 1188 eyes): sensitivity 0.51 (95% CI 0.25, 0.76), specificity 0.92 (95% CI 0.70, 0.98) (low-certainty); SPAC (≤ 5 and/or S or P) (4 studies, 4677 eyes): sensitivity 0.83 (95% CI 0.70, 0.91), specificity 0.78 (95% CI 0.70, 0.83) (moderate-certainty); Scheimpflug photography (central ACD) (9 studies, 1698 eyes): sensitivity 0.92 (95% CI 0.84, 0.96), specificity 0.86 (95% CI 0.76, 0.93) (moderate-certainty); AS-OCT (subjective opinion of occludability) (13 studies, 9242 eyes): sensitivity 0.85 (95% CI 0.76, 0.91); specificity 0.71 (95% CI 0.62, 0.78) (moderate-certainty). For comparisons of sensitivity and specificity between index tests we used LACD (≤ 25%) as the reference category. The flashlight test (grade 1 threshold) showed a statistically significant lower sensitivity than LACD (≤ 25%), whereas AS-OCT (subjective judgement) had a statistically significant lower specificity. There were no statistically significant differences for the other index test comparisons. A subgroup analysis was conducted for LACD (≤ 25%), comparing community (7 studies, 14.4% prevalence) vs secondary care (7 studies, 42% prevalence) settings. We found no evidence of a statistically significant difference in test performance according to setting. Performing LACD on 1000 people at risk of angle closure with a prevalence of occludable angles of 10%, LACD would miss about 17 cases out of the 100 with occludable angles and incorrectly classify 108 out of 900 without angle closure. The finding that LACD performed as well as index tests that use sophisticated imaging technologies, confirms the potential for this test for case-detection of occludable angles in high-risk populations. However, methodological issues across studies may have led to our estimates of test accuracy being higher than would be expected in standard clinical practice. There is still a need for high-quality studies to evaluate the performance of non-invasive tests for angle assessment in both community-based and secondary care settings.

Predictive Value of Screening Tests for Visually Significant Eye Disease

To determine the predictive value of ophthalmic screening tests with visually significant eye disease in a cohort of American Indian/Alaskan Natives from the Pacific Northwest. Validity assessment of a possible screening protocol. Ophthalmic technicians performed a screening examination including medical and ocular history, best-corrected visual acuity, limbal anterior chamber depth assessment, frequency-doubling technology perimetry (FDT, C-20-5), confocal scanning laser ophthalmoscopy, nonmydriatic digital photography, and tonometry on 429 participants. An ophthalmologist performed a comprehensive eye examination on subjects with 1 or more abnormal screening tests and a random selection of those with normal screening tests. We used univariate and multivariate logistic regression to determine the association between abnormal screening test results and visually significant eye disease. We also determined the predictive value of screening tests with ocular disease. Univariate analysis identified history of eye disease or diabetes mellitus (P < .001), visual acuity <20/40 (P < .001), abnormal/poor-quality confocal scanning laser ophthalmoscopy (P < .001), abnormal FDT (P < .001), and abnormal/poor-quality nonmydriatic imaging (P < .001) as associated with visually significant eye disease. A multivariate analysis found visually significant eye disease to be associated (P < .001; receiver operating characteristic curve area= 0.827, negative predictive value= 84%) with 4 screening tests: visual acuity <20/40, abnormal/poor-quality nonmydriatic imaging, abnormal FDT, and abnormal/poor-quality confocal scanning laser ophthalmoscopy. Ophthalmic technicians performing a subset of screening tests may provide an accurate and efficient means of screening for eye disease in an American Indian/Alaskan Native population. Confirmation of these results in other populations, particularly those with a different profile of disease prevalence, is needed.

Agreement among optometrists and ophthalmologists in estimating limbal anterior chamber depth using the van Herick method

To evaluate the inter-observer agreement for measuring limbal anterior chamber depth (LACD) using the van Herick test in community optometrists, glaucoma specialist optometrists and ophthalmologists. The study was divided into two phases. In the first phase, a random sample of 100 UK community optometrists were given an opportunity to select and grade eight digital slit-lamp images of anterior chamber angles using the original van Herick 4 point grading scale. The images were included in a clinical decision making study using computerised virtual case vignettes. In the second phase, hospital-based glaucoma specialist optometrists and glaucoma sub-specialist ophthalmologists graded the LACD of the right eye using a 7-point % grading scale in 57 consecutively presenting patients with suspect glaucoma. Inter-observer agreement was assessed using linearly weighted kappa (κw ). Inter-observer agreement for community optometrists was moderate, with a mean κw for grading photographic images of 0.50 (95% confidence interval (CI) 0.43-0.57). Overall, ninety-two percent of observations were within one grade of the actual grade, although grading of narrow angles was associated with a 13% false negative error rate (based on a≤grade 2 threshold). For Phase 2 of the study, pairwise comparisons between optometrists and ophthalmologists showed that agreement was moderate to substantial (mean κw =0.54-0.65) with a false negative rate of 1.9% (based on a≤25% threshold). Grading accuracy of specialist optometrists and ophthalmologists were equivalent. In summary, the present study found that community optometrists showed moderate inter-observer agreement for grading LACD. Glaucoma specialist optometrists showed moderate to substantial agreement with weighted kappa values that were equivalent to sub-specialist ophthalmologists. The augmented 7-point % grading scale is intuitive and potentially offers greater accuracy for grading narrow angles than the traditional 4-point scale for grading LACD.

Méthode de dépistage du glaucome chronique par fermeture de l’angle basée sur l’utilisation systématique du GDxVCC et de la gonioscopie photodynamique. Résultats à un an d’une iridotomie systématique

Angle closure glaucoma, a recognized major world health issue disproportionately affecting women and Asians, is not often considered in our European populations, normotensive subjects, myopic patients, or subjects with a deep anterior chamber. Early diagnosis is worthwhile, as laser peripheral iridotomy (LPI) is an effective one-step treatment of the causal mechanism. We have performed a retrospective study of patients who underwent an LPI, the indication for which was based on "photodynamic" gonioscopy in a darkened room showing iridotrabecular contact in darkness. Such photodynamic gonioscopy was motivated by the presence of even minute defects in the nerve fiber layer as seen on the GDxVCC or the presence of a Van Herick sign (narrow limbal anterior chamber depth). One hundred and three eyes of 103 patients underwent LPI and a minimum 1-year follow-up (mean follow-up almost 2 years). Mean age was 63.7±11.8 years, and women accounted for 63.1% of cases. The vast majority (78.6%) of patients had neither glaucoma nor ocular hypertension. There were 60.1% hyperopes and 39.9% myopes. Over half (57%) had a deep or a very deep anterior chamber. After LPI, there was immediate deepening of the limbal depth of the anterior chamber in 100% of cases. The aqueous humor that flowed forward was almost always viscous-looking. After 1 year, the IOP was 1.3mm Hg±2.4 lower (P<.001) (t test). All patients who had experienced morning headaches (44% of patients) were relieved of this symptom. GDxVCC after 1 year was clearly improved in 18% of cases, slightly improved in 20%, stable in 50%, slightly worse in 11% of cases, and clearly worse in 1%. Cases treated at an earlier stage had a better improvement in GDxVCC. Our study shows frequent chronic angle closure in our European population even with deep anterior chambers. Absence of a Van Herick sign does not rule out angle closure at night. A photodynamic gonioscopy with the Goldmann three-lens mirror (to avoid unintentional indentation with the small diameter lenses in these normotensive eyes) should be performed in a darkened room. LPI is an effective one-step treatment of the underlying cause, that is particularly beneficial if performed early.

Re: The portsmouth-based refinement scheme: a role for virtual clinics in the future?

Sir, We read with interest the Portsmouth Glaucoma Referral Refinement Scheme findings.1 The scheme does highlight the potential benefits in the current burden of waiting times and costs on the NHS since the introduction of the NICE guidelines. Interestingly, there was no mention of angle closure suspects in this report. A similar glaucoma referral refinement scheme in our hospital is run by a glaucoma-trained optometrist and has been in place for the last 14 months. In this clinic, patients have a series of tests similar to the ones described by the authors, but we also document Van Herick test in all patients and the patients with peripheral limbal anterior chamber depth less than 25% corneal thickness are referred to consultant-led clinics for gonioscopy and further evaluation. A recent audit of our referral refinement clinic over 3 months showed that out of 35 patients seen, 22 were referred to the consultant clinic. This included three cases (13.6%) with narrow angles with Van Herick less than 25% of corneal thickness. Primary angle closure was confirmed in all three of these cases, and they went on to have laser iridotomy. We would be keen to know if the authors can share their data on angle closure suspects detected in their scheme.

Response to Shah et al

Sir, We thank Shah et al1 for their interest in the Portsmouth Glaucoma Refinement Scheme.2 The scheme also uses Van Herick grading for anterior chamber depth—all patients with a Van Herick peripheral limbal anterior chamber depth of less than 25% of corneal thickness were referred to the virtual clinic for assessment by an ophthalmologist. Approximately 10% of all of those accepted from the Refinement Scheme virtual clinic to HES (from a total of 11 out of 100 referred to the virtual clinic, from our audit) were due to narrow angles suspected through Van Herick grading. Of these, 25% subsequently required laser peripheral iridotomy, slightly higher than the 17% positive predictive value, for the suggestion of occludable angles by an initial Van Herick test, outlined by Foster.3

Comparing approaches to screening for angle closure in older Chinese adults

Primary angle-closure glaucoma is expected to account for nearly 50% of bilateral glaucoma blindness by 2020. This study was conducted to assess the performance of the scanning peripheral anterior chamber depth analyzer (SPAC) and limbal anterior chamber depth (LACD) as screening methods for angle closure. This study assessed two clinical populations to compare SPAC, LACD, and gonioscopy: the Zhongshan Angle-closure Prevention Trial, from which 370 patients were eligible as closed-angle participants and the Liwan Eye Study, from which 72 patients were selected as open-angle controls. Eligible participants were assessed by SPAC, LACD, and gonioscopy. Angle status was defined by gonioscopy. Area under the receiver operating characteristic curve (AUROC) for SPAC was 0.92 (0.89-0.95) whereas AUROC for LACD was 0.94 (0.92-0.97). Using conventional cutoff points, sensitivity/specificity was 93.0%/70.8% for SPAC and 94.1%/87.5% for LACD. Sequential testing using both SPAC and LACD increased the specificity to 94.4% and decreased the sensitivity to 87.0%. SPAC has significantly lower specificity than LACD measurement using conventional cutoffs but interpretation of the findings can be performed by modestly trained personnel.

Anterior Chamber Angle Assessment Techniques

Angle-closure glaucoma is a leading cause of irreversible blindness. Diagnosis and treatment are intricately related to angle assessment techniques. This article reviews the literature on angle assessment and provides recommendations about optimal techniques based on the published evidence. Specifically, we review gonioscopy, ultrasound biomicroscopy, and anterior segment optical coherence tomography, all of which can be used to assess the anterior chamber angle directly. In addition, we discuss surrogate approaches to measuring the angle configuration, including limbal anterior chamber depth measurement, scanning peripheral anterior chamber depth measurement, and Scheimpflug photography.

Laser Peripheral Iridotomy in Primary Angle-Closure Suspects: Biometric and Gonioscopic Outcomes: The Liwan Eye Study

Purpose To assess the immediate effect of laser peripheral iridotomy (LPI) and mechanisms of angle closure in a population-based study of primary angle closure (PAC) suspects. Design Prospective interventional study. Participants People identified as PAC suspects aged 50 to 79 years from a population-based survey in Guangzhou, China. Intervention Laser peripheral iridotomy was performed in 1 randomly selected eye. Examinations were carried out before and 2 weeks after the intervention. Main Outcome Measures Intraocular pressure (IOP), ultrasound biometry, optical pachymetry, and gonioscopy. Results A total of 72 people with bilateral suspected PAC participated in the study. Mean IOP decreased by 3 mmHg (P<0.001), but axial anterior chamber depth did not change significantly (P = 0.784) after LPI. Median limbal anterior chamber depth increased from 15% to 25% of peripheral corneal thickness (P<0.001, Wilcoxon signed-rank test). Median iridotrabecular angle width increased from 0° to 10° in the superior quadrant and from 10° to 30° in the inferior quadrant (P<0.001). Nevertheless, 14 eyes (19.4%) still had 3 or more quadrants in which the posterior (usually pigmented) trabecular meshwork could not be seen after laser iridotomy. Conclusions This study confirms that LPI results in a significant increase in the angle width in Chinese people with narrow angles. However, one fifth of eyes had residual angle closure after LPI. Although this report confirms that iridotomy widens the anterior chamber angle in most PAC suspects, long-term prospective studies with a larger sample size are required to determine if the risks of PAC glaucoma and other related pathologic sequelae are reduced after prophylactic LPI and to investigate the risk-to-benefit ratio before recommending widespread use of prophylactic LPI in this population. To assess the immediate effect of laser peripheral iridotomy (LPI) and mechanisms of angle closure in a population-based study of primary angle closure (PAC) suspects. Prospective interventional study. People identified as PAC suspects aged 50 to 79 years from a population-based survey in Guangzhou, China. Laser peripheral iridotomy was performed in 1 randomly selected eye. Examinations were carried out before and 2 weeks after the intervention. Intraocular pressure (IOP), ultrasound biometry, optical pachymetry, and gonioscopy. A total of 72 people with bilateral suspected PAC participated in the study. Mean IOP decreased by 3 mmHg (P<0.001), but axial anterior chamber depth did not change significantly (P = 0.784) after LPI. Median limbal anterior chamber depth increased from 15% to 25% of peripheral corneal thickness (P<0.001, Wilcoxon signed-rank test). Median iridotrabecular angle width increased from 0° to 10° in the superior quadrant and from 10° to 30° in the inferior quadrant (P<0.001). Nevertheless, 14 eyes (19.4%) still had 3 or more quadrants in which the posterior (usually pigmented) trabecular meshwork could not be seen after laser iridotomy. This study confirms that LPI results in a significant increase in the angle width in Chinese people with narrow angles. However, one fifth of eyes had residual angle closure after LPI. Although this report confirms that iridotomy widens the anterior chamber angle in most PAC suspects, long-term prospective studies with a larger sample size are required to determine if the risks of PAC glaucoma and other related pathologic sequelae are reduced after prophylactic LPI and to investigate the risk-to-benefit ratio before recommending widespread use of prophylactic LPI in this population.

Noncontact Goniometry With Optical Coherence Tomography

To assess the value of noncontact goniometry with optical coherence tomography (OCT) compared with current clinical parameters in the evaluation of the anterior chamber angle (ACA). Prospective observational study of 138 eyes of 109 patients. The ACA parameters and angle-opening distance (AOD) were measured with slitlamp-adapted OCT goniometry. The iris and scleral thickness and the iris convexity were assessed with OCT. Both ACA and AOD were compared with the clinical parameters of gonioscopy grade, limbal anterior chamber depth (ACD), ultrasonographic central ACD, and lens-axial length (LAL) ratio. Noncontact goniometry with OCT revealed mean +/- SD values of 28 degrees +/- 16 degrees for the ACA and 381 +/- 234 mum for the AOD. The mean +/- SD iris thickness was 369 +/- 84 mum, and the scleral thickness at the scleral spur was 943 +/- 148 mum. There was a significant correlation (P<.001) with the clinical parameters of gonioscopic grading, limbal ACD, ultrasonographic central ACD, and LAL ratio. The sensitivity and specificity of OCT goniometry to detect an occludable angle were 86% and 95% for ACA and 85% and 90% for AOD, respectively. Noncontact goniometry with OCT was helpful in evaluating the anterior chamber structures and as a screening modality. Goniometry with OCT could improve the noninvasive clinical assessment and treatment of patients with glaucoma.

A prospective ultrasound biomicroscopy evaluation of changes in anterior segment morphology after laser iridotomy in asian eyes

Purpose To prospectively quantify changes in anterior segment morphology after laser iridotomy using gonioscopy and ultrasound biomicroscopy (UBM). Design Prospective comparative observational case series. Participants Fifty-five fellow eyes of patients presenting with acute primary angle closure (APAC). Methods The fellow eyes of patients presenting with APAC were examined with UBM, A-scan ultrasonography, and optical pachymetry at presentation and 2 weeks after sequential argon/neodymium yttrium–aluminum–garnet laser peripheral iridotomy (LPI). UBM images were analyzed using UBM Pro 2000 software. Baseline measurements were made both under standard lighting conditions and in darkness to look for changes in anterior segment findings. Main outcome measures The degree of angle opening was measured using the angle-opening distance (AOD) at 250 and 500 μm from the scleral spur (AOD250 and AOD500, respectively) and angle recess area (ARA). Results Fifty-five Asian patients were examined; AOD250, AOD500, and ARA all significantly increased after sequential laser iridotomy ( P < 0.002). Gonioscopic grading of the angle opening significantly increased in all 4 quadrants ( P < 0.001). The Van Herick grade of limbal anterior chamber depth increased ( P < 0.001), whereas the number of eyes classified as occludable decreased (73%–33%, P < 0.001). Anterior chamber depth did not change significantly (2.41 mm ± 0.28 mm vs. 2.42 mm ± 0.30 mm, P = 0.43) as measured with optical pachymetry. Increased illumination increased the angle-opening measures, but induced a different alteration in peripheral iris morphology. Illumination-induced changes were greater after iridotomy than before laser treatment. Conclusions In Asian eyes at high risk of developing APAC, sequential LPI produced a significant widening of the anterior chamber angle without deepening the anterior chamber centrally. LPI produces changes in iris morphology that are different from those caused by an increase in illumination, indicating that different mechanisms account for angle opening under these 2 conditions.