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Angle closure extent, anterior segment dimensions and intraocular pressure
  1. Natalia Porporato1,2,
  2. Rachel Chong1,2,
  3. Benjamin Y Xu3,
  4. Tin A Tun1,2,
  5. Joanne HuiMin Quah4,
  6. Marcus Tan5,
  7. Mani Baskaran1,
  8. Ching Yu Cheng1,2,
  9. Tin Aung1,2,6
  1. 1 Glaucoma, Singapore Eye Research Institute, Singapore National Eye Centre, Singapore
  2. 2 DUKE-NUS Medical School, Singapore
  3. 3 Ophthalmology, University of Southern California Keck School of Medicine, Los Angeles, California, USA
  4. 4 Outram Polyclinic, SingHealth Polyclinics, Singapore
  5. 5 Ophthalmology, National University Hospital, National University of Singapore, Singapore
  6. 6 Yong Loo Lin School of Medicine, National University of Singapore, Singapore
  1. Correspondence to Dr Tin Aung, Glaucoma Services, Singapore Eye Research Institute, Singapore 168751, Singapore; aung.tin{at}


Aim To investigate the association between the extent of iridotrabecular contact and other quantitative anterior segment dimensions measured by swept-source optical coherence tomography (SS-OCT; CASIA SS-1000, Tomey, Nagoya, Japan) with intraocular pressure (IOP).

Methods Cross-sectional study. All subjects who were ≥50 years with no history of glaucoma, ocular surgery or trauma, underwent SS-OCT imaging (eight equally spaced radial scans), Goldman applanation tonometry and gonioscopy on the same day. We measured iridotrabecular contact (ITC) index and area, total volume of trabeculo-iris space area and angle opening distance at 500 and 750 from the scleral spur (TISA 500 and 750, AOD 500 and 750, respectively), anterior chamber depth (ACD), volume, area and width, pupil diameter, lens vault and iris volume.Their relationship with IOP (dependent variable) was assessed by locally weighted scatterplot smoothing (Lowess) regression with change-point analysis and generalised additive models adjusted for confounders.

Results 2027 right eyes of mostly Chinese Singaporeans (90%) were analysed. ITC index above a threshold of ~60% (95% CI 34% to 92%) was significantly associated with higher IOP. Independent of the extent of ITC, ACD was also significantly associated with higher IOP below a threshold of 2.5 mm (95% CI 2.33 mm to 2.71 mm). Greater ITC index and shallower ACD had a joint association with IOP. A model including ACD and ITC index was more predictive of IOP than a model considering these variables separately, particularly for women with gonioscopically closed angles (R2 52.7%, p<0.05).

Conclusions The extent of angle closure and the ACD below a certain threshold had a significant joint association with IOP. These parameters, as biometrical surrogates of mechanical obstruction of the aqueous outflow, may jointly contribute to elevated IOP, particularly in women with gonioscopic angle closure.

  • intraocular pressure
  • angle
  • anterior chamber
  • glaucoma
  • imaging

Data availability statement

Data are available on reasonable request. Data are available upon request.

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Data availability statement

Data are available on reasonable request. Data are available upon request.

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  • Contributors Study design and data collection: NP, TAT, JHMQ, MT, MB and TA. Analysis and interpretation of data: NP and CYC. Drafting and revision: NP, RC, BYX and TA. All authors reviewed and approved the final manuscript. Guarantor: AT.

  • Funding Biomedical Research Council 10/1/35/19/674 and A Star Biomedical Engineering Programme Grant 152/148/0034.

  • 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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