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Investigating the determinants of iridolenticular contact area: a novel parameter for angle closure
  1. Tin A Tun1,2,
  2. Monisha Esther Nongpiur1,2,
  3. Benjamin Y Xu3,
  4. Xiaofei Wang4,
  5. Marcus Tan1,5,
  6. Joanne Hui Min Quah6,
  7. Hou-Boon Lim1,
  8. Ching Yu Cheng1,2,
  9. Tin Aung1,2
  1. 1 Singapore Eye Research Institute and Singapore National Eye Centre, Singapore
  2. 2 Duke-NUS Medical School, Singapore
  3. 3 Department of Ophthalmology, USC Roski Eye Institute, Keck School of Medicine, University of Southern California, Los Angeles, California, USA
  4. 4 Key Laboratory for Biomechanics and Mechanobiology of Ministry of Education, Beijing Advanced Innovation Center for Biomedical Engineering, School of Biological Science and Medical Engineering, Beihang University, Beijing, China
  5. 5 Ophthalmology Service, Jurong Health Service, Singapore
  6. 6 SingHealth Polyclinics, Outram, Singapore
  1. Correspondence to Dr Tin Aung, Glaucoma, Singapore National Eye Centre Glaucoma Department, Singapore 168751, Singapore; aung.tin{at}snec.com.sg

Abstract

Background/aims To identify ocular determinants of iridolenticular contact area (ILCA), a recently introduced swept-source optical coherence tomography (SSOCT) derived parameter, and assess the association between ILCA and angle closure.

Methods In this population-based cross-sectional study, right eyes of 464 subjects underwent SSOCT (SS-1000, CASIA, Tomey Corporation, Nagoya, Japan) imaging in the dark. Eight out of 128 cross-sectional images (evenly spaced 22.5° apart) were selected for analysis. Matlab (Matworks, Massachusetts, USA) was used to measure ILCA, defined as the circumferential extent of contact area between the pigmented iris epithelium and anterior lens surface. Gonioscopic angle closure (GAC) was defined as non-visibility of the posterior trabecular meshwork in two or more angle quadrants.

Results The mean age of subjects was 62±6.6 years, with the majority being female (65.5%). 143/464 subjects (28.6%) had GAC. In multivariable linear regression analysis, ILCA was significantly associated with anterior chamber width (β=1.03, p=0.003), pupillary diameter (β=−1.9, p<0.001) and iris curvature (β=−17.35, p<0.001). ILCA was smaller in eyes with GAC compared with those with open angles (4.28±1.6 mm2 vs 6.02±2.71 mm2, p<0.001). ILCA was independently associated with GAC (β=−0.03, p<0.001), iridotrabecular contact index (β=−6.82, p<0.001) or angle opening distance (β=0.02, p<0.001) after adjusting for covariates. The diagnostic performance of ILCA for detecting GAC was acceptable (AUC=0.69).

Conclusions ILCA is a significant predictor of angle closure independent of other biometric factors and may reflect unique anatomical information associated with pupillary block. ILCA represents a novel biometric risk factor in eyes with angle closure.

  • Anterior chamber
  • Glaucoma
  • Imaging
  • Iris
  • Lens and zonules

Data availability statement

Data are available on reasonable request.

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Data availability statement

Data are available on reasonable request.

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Footnotes

  • X @BenXuLab

  • Contributors Design of study (TAT, MEN, JHMQ, CYC and TA); Conduct of the study (TAT, MEN, XW and MT); Collection and management of data (TAT, XW, BYX, H-BL and TA); Analysis and Interpretation of data (TAT, MEN, XW, BYX, CYC and TA); Preparation of manuscript (TAT, MEN, XW, BYX, H-BL and TA); Review or approval of manuscript (MT, JHMQ, H-BL, CYC and TA). TA is the guarantor of the manuscript.

  • Funding The study was supported by the National Medical Research Council (TA; NMRC/STAR/0023/2014 and MOH-000435) and the National Natural Science Foundation of China (XW; 12002025).

  • Disclaimer The sponsor or funding organisation had no role in the design or conduct of this research. The views expressed are those of the author(s) and not necessarily those of the NMRC, Singapore.

  • Competing interests None declared.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.

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