Peripheral iris thickness and association with iridotrabecular contact after laser peripheral iridotomy in patients with primary angle-closure and primary angle-closure glaucoma

Iris Morphological and Biomechanical Factors Influencing Angle Closure During Pupil Dilation

Purpose

To use finite element (FE) analysis to assess what morphologic and biomechanical factors of the iris and anterior chamber are more likely to influence angle narrowing during pupil dilation.

Methods

The study consisted of 1344 FE models comprising the cornea, sclera, lens, and iris to simulate pupil dilation. For each model, we varied the following parameters: anterior chamber depth (ACD = 2-4 mm) and anterior chamber width (ACW = 10-12 mm), iris convexity (IC = 0-0.3 mm), iris thickness (IT = 0.3-0.5 mm), stiffness (E = 4-24 kPa), and Poisson's ratio (v = 0-0.3). We evaluated the change in (△∠) and the final dilated angles (∠f) from baseline to dilation for each parameter.

Results

The final dilated angles decreased with a smaller ACD (∠f = 53.4° ± 12.3° to 21.3° ± 14.9°), smaller ACW (∠f = 48.2° ± 13.5° to 26.2° ± 18.2°), larger IT (∠f = 52.6° ± 12.3° to 24.4° ± 15.1°), larger IC (∠f = 45.0° ± 19.2° to 33.9° ± 16.5°), larger E (∠f = 40.3° ± 17.3° to 37.4° ± 19.2°), and larger v (∠f = 42.7° ± 17.7° to 34.2° ± 18.1°). The change in angles increased with larger ACD (△∠ = 9.37° ± 11.1° to 15.4° ± 9.3°), smaller ACW (△∠ = 7.4° ± 6.8° to 16.4° ± 11.5°), larger IT (△∠ = 5.3° ± 7.1° to 19.3° ± 10.2°), smaller IC (△∠ = 5.4° ± 8.2° to 19.5° ± 10.2°), larger E (△∠ = 10.9° ± 12.2° to 13.1° ± 8.8°), and larger v (△∠ = 8.1° ± 9.4° to 16.6° ± 10.4°).

Conclusions

The morphology of the iris (IT and IC) and its innate biomechanical behavior (E and v) were crucial in influencing the way the iris deformed during dilation, and angle closure was further exacerbated by decreased anterior chamber biometry (ACD and ACW).

Association of peripheral anterior synechiae with anterior segment parameters in eyes with primary angle closure glaucoma

To investigate the association of peripheral anterior synechiae (PAS) with intraocular pressure (IOP) and anterior-segment parameters in subjects with primary angle-closure glaucoma (PACG). A total of 267 subjects with PACG were recruited and underwent gonioscopy and anterior-segment optical coherence tomography (ASOCT). Customized software was used to measure ASOCT parameters, including angle opening distance (AOD750) and trabecular-iris-space-area (TISA750) at 750 µm from the scleral spur, anterior chamber depth, width, area and volume (ACD, ACW, ACA, ACV), iris thickness (IT750), iris area (IAREA), and lens vault (LV). Presenting IOP was defined as the first IOP reading before the initiation of IOP-lowering treatment. The mean age of the 267 subjects was 67.0 ± 8.9 years, 140 (52.4%) were male, and 246 (92.1%) were of Chinese ethnicity. PAS was present in 122 (45.7%) subjects, and was most frequently found in the superior quadrant (79.5%). Subjects with PAS had greater presenting IOP (28.7 ± 12.9 vs 22.4 ± 9.7 mmHg, p < 0.001), narrower AOD750 (p < 0.001), smaller TISA750 (p < 0.001), ACD (p = 0.04), ACA (p = 0.02), ACV (p = 0.01) and larger LV (p = 0.01) compared to PACG eyes without PAS. No significant differences were noted for iris parameters. A multivariate logistic regression analysis showed that higher presenting IOP (β = 0.20, p < 0.001), worse visual field mean deviation (β = - 0.20, p = 0.01) and narrower AOD750 (β = - 0.25, p = 0.03) were the only parameters that significantly correlated with the extent of PAS in clock hours. Almost one-half of the subjects with PACG demonstrated PAS; these eyes were associated with higher presenting IOP, smaller anterior segment dimensions and more severe disease.

Quantification of Iridotrabecular Contact in Primary Angle-Closure Disease

PRECIS

Iridotrabecular contact (ITC), a measure of angle closure, can be quantified along with other angle parameters on anterior segment optical coherence tomography (ASOCT). Hence, angle changes and angle closure mechanisms can be detected predicting the efficacy of iridotomy.

PURPOSE

To assess 360-degree ITC and ocular parameter changes, after laser peripheral iridotomy (LPI), in primary angle-closure disease (PACD) subgroups.

METHODOLOGY

This was a prospective observational study including 90 subjects, 30 each of primary angle-closure suspect (PACS), primary angle closure (PAC), and primary angle-closure glaucoma (PACG). Anterior segment OCT parameters were measured before and 3 weeks after LPI ITC: central anterior chamber depth, lens vault, angle-opening distance, angle recess area, trabecular iris space area, trabecular iris angle at 500 and 750 μm from scleral spur.

RESULTS

ITC was highest in PACG, 81.43%±22.39%, followed by PAC, 28.53%±21.30%, and PACS, 10.76%± 8.54% (P=0.011). There was a significant decrease in ITC in all 3 groups after iridotomy (P<0.001), with a residual ITC of 68.56%±26.44% in PACG, 18.23%±15.98% in PAC, and 5.13%±5.11% in PACS. A significant positive correlation was seen between the extent of ITC, baseline intraocular pressure, and visual field index. ITC was highest in eyes with exaggerated lens vault (77.3%±32.03%), as compared with eyes having a plateau iris configuration or relative pupillary block configuration (P<0.001).

CONCLUSIONS

Iridotomy at any stage of PACD shows a significant decrease in ITC, with areas of residual ITC. Even in PACG, the iridotomy is effective in exposing parts of the trabecular meshwork that had contact earlier. Greater baseline ITC and postlaser ITC are a biomarker for higher intraocular pressure and greater visual field damage, which need lifelong review and appropriate management.

Factors Associated with Interventions after Laser Peripheral Iridotomy for Primary Angle-Closure Spectrum Diagnoses

PURPOSE

To assess factors associated with receipt of subsequent medical, laser, or surgical interventions after laser peripheral iridotomy (LPI).

DESIGN

Retrospective review.

PARTICIPANTS

A total of 1271 eyes in 692 subjects with narrow angles (NAs) that were treated with LPI.

METHODS

Demographic and clinical factors associated with primary angle-closure (PAC) or PAC glaucoma (PACG) versus PAC suspect (PACS) diagnosis and use of glaucoma medications at the time of LPI, as well as factors predictive of subsequent addition of glaucoma medications, and receipt of selective laser trabeculoplasty (SLT), cataract surgery, and glaucoma surgery were assessed using logistic regression with generalized estimating equations. Kaplan-Meier curves and Cox proportional-hazards regression analysis were used to assess baseline factors affecting the time to SLT, cataract surgery, or glaucoma surgery.

MAIN OUTCOME MEASURES

Diagnosis of PAC/PACG and medical, laser, or surgical interventions after LPI.

RESULTS

African Americans (odds ratio [OR], 2.12; P < 0.001) were significantly more likely than whites to have PAC/PACG than PACS and to already be taking glaucoma medications (OR, 2.25, P < 0.001) at the time of LPI. In multivariable logistic regression analysis, African Americans were significantly more likely to be prescribed additional glaucoma medications after LPI (OR, 1.73; P = 0.025) and receive glaucoma surgery (OR, 2.7; P = 0.007), but were less likely to receive SLT (OR, 0.37; P = 0.009). In multivariate Cox proportional-hazards regression analysis, African Americans had longer time to SLT than whites (hazard ratio [HR], 0.41; P = 0.022), but a shorter time to glaucoma surgery (HR, 2.57; P = 0.004). There was no significant association between race and the likelihood of cataract surgery or time to cataract surgery (P > 0.10).

CONCLUSIONS

African Americans were more likely than whites to carry a diagnosis of PAC or PACG at the time of LPI and were significantly more likely to be prescribed additional glaucoma medications and require glaucoma surgery after LPI. Improved screening methods that target African Americans with NAs are needed so that preventive interventions such as LPI can be performed earlier to decrease the risk of progression.

Pupil Size Associated with the Largest Iris Volume in Normal Chinese Eyes

Background

To determine the range of pupil size that has the largest iris volume in normal eyes.

Methods

31 healthy adult Chinese volunteers underwent swept-source anterior segment OCT examination in both eyes. Pilocarpine 1% was instilled in a randomly selected eye (eye with induced miosis (ME)) of each participant to obtain iris volume (IV) measurements over a range of pupil sizes. OCT was performed prior to and one hour after pilocarpine in both ME and fellow eye (FE). Iris volume (IV), anterior chamber volume (ACV), anterior chamber depth (ACD), and pupil size (PS) were recorded. A scatter plot was used to depict the association between each pupil size and IV.

Results

The pupillary sizes for which IV was recorded in ME and FE ranged from 1.161 mm to 6.665 mm. The mean IV increased with miosis in both ME and FE; in 13 eyes, IV decreased with a decrease in pupillary size. PS between 3.812 and 6.665 mm was associated with an increase in IV, while PS between 3.159 and 5.54 mm was associated with a decrease. The relationship between PS and IV was in the shape of a downward parabola and was modeled using a quadratic equation (y = −1.3121x² + 8.8429x + 16.423, R² = 0.26886). The largest IV occurred at PS between 3 and 4 mm.

Conclusions

The relationship between PS and IV in this study was in the shape of a downward parabola. The largest IV was recorded at a pupillary size between 3 and 4 mm. This trial is registered with ChiCTR-ROC-17013572.

Contemporary approach to the diagnosis and management of primary angle-closure disease

The primary angle-closure disease spectrum varies from a narrow angle to advanced glaucoma. A variety of imaging technologies may assist the clinician in determining the pathophysiology and diagnosis of primary angle closure, but gonioscopy remains a mainstay of clinical evaluation. Laser iridotomy effectively eliminates the pupillary block component of angle closure; however, studies show that, in many patients, the iridocorneal angle remains narrow from underlying anatomic issues, and increasing lens size often leads to further narrowing over time. Recent studies have further characterized the role of the lens in angle-closure disease, and cataract or clear lens extraction is increasingly used earlier in its management. As a first surgical step in angle-closure glaucoma, lens extraction alone often effectively controls the pressure with less risk of complications than concurrent or stand-alone glaucoma surgery, but may not be sufficient in more advanced or severe disease. We provide a comprehensive review on the primary angle-closure disease nomenclature, imaging, and current laser and surgical management.

Risk Factors Associated with Missed Diagnoses of Narrow Angles by the Van Herick Technique

PURPOSE

To identify which factors are associated with a deep-appearing anterior chamber on slit-lamp examination by the Van Herick (VH) technique in eyes with a diagnosis of narrow angle (NA) on gonioscopy.

DESIGN

Retrospective review.

PARTICIPANTS

One thousand three hundred fourteen eyes in 696 participants with NA on indirect gonioscopy.

METHODS

All included eyes were graded as narrow with iridotrabecular contact on indirect gonioscopy in a darkened room by a single trained glaucoma specialist. Before gonioscopy, eyes were graded as narrow or deep by VH slit-lamp examination technique. Demographic and clinical factors predictive of a deep VH grading were assessed using logistic regression with generalized estimating equations.

MAIN OUTCOME MEASURES

Factors associated with deep versus narrow VH grade.

RESULTS

Using the VH technique, 13.7% of eyes (n = 180/1314) with NA on gonioscopy were classified as deep. Eyes with primary angle-closure glaucoma (PACG; odds ratio, 2.43; P < 0.001) and primary angle closure (PAC; odds ratio, 1.38; P = 0.006) were significantly more likely to be graded as deep by the VH technique relative to eyes that were primary angle-closure suspects (PACSs). In multivariate analysis, male gender (odds ratio, 2.22; P < 0.001), myopia (odds ratio, 1.4; P = 0.048), and black (odds ratio, 4.11; P < 0.001) and Asian (odds ratio, 2.24; P = 0.044) race were independent risk factors for a deep grading with the VH technique in eyes with NA on gonioscopy.

CONCLUSIONS

Patients with NAs on gonioscopy who are men, myopic, and of black or Asian race are at increased risk of being misdiagnosed with deep angles if examined with the VH technique alone. Eyes with PACG and PAC may be more likely than those with PACS to be misdiagnosed as deep with the VH technique. It is possible that by being missed by the VH technique, these eyes could have progressed from PACS to PAC and PACG. Patients with these demographic and clinical characteristics in the presence of other risk factors for glaucoma should undergo careful gonioscopy.