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Novel anterior-chamber angle measurements by high-definition optical coherence tomography using the Schwalbe line as the landmark
  1. Carol Y Cheung1,
  2. Ce Zheng1,
  3. Ching-Lin Ho1,
  4. Tin A Tun1,
  5. Rajesh S Kumar1,
  6. Fouad El Sayyad1,
  7. Tien Y Wong1,2,3,
  8. Tin Aung1,2
  1. 1Singapore Eye Research Institute and Singapore National Eye Centre, Singapore
  2. 2Department of Ophthalmology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore
  3. 3Centre for Eye Research Australia, University of Melbourne, Royal Victorian Eye and Ear Hospital, Victoria, Australia
  1. Correspondence to Dr Tin Aung, Singapore Eye Research Institute, 11 Third Hospital Avenue, Singapore 168751; tin11{at}


Objective To propose the Schwalbe line (SL) as a new anatomical landmark, independent of the scleral spur (SS) location, for assessing anterior chamber angle (ACA) width quantitatively with high-definition optical coherence tomography (HD-OCT).

Methods Study subjects underwent dark-room gonioscopy and HD-OCT in one randomly selected eye. The authors developed a computer-aided program to define two new quantitative parameters for assessing ACA width: Schwalbe line-angle opening distance (SL-AOD) measured at the SL, and Schwalbe line-trabecular–iris space area (SL-TISA) measured 500 μm from the SL. The associations between SL parameters, SS parameters and gonioscopic grading were evaluated.

Results Seventy-three (47 females, 26 males) subjects were recruited, the majority of whom were Chinese (89%). The authors excluded 29 images (19.9%) owing to poor image quality, leaving 117 HD-OCT images (65 nasal, 52 temporal) for analysis. SL and SS could be identified in 95% and 85% of quadrants respectively (p=0.035). SL-AOD and SL-TISA were significantly correlated with SS parameters (all r≥0.85) and gonioscopic grading (all r≥0.69). In eyes with closed angles (n=36), SL parameters showed strong correlations with gonioscopic grading (r ranged from 0.43 to 0.44).

Conclusions Novel angle parameters, based on SL as a landmark, may be useful to quantify ACA width and to assess for risk of angle closure.

  • Angle-closure glaucoma
  • anterior chamber angle
  • optical coherence tomography
  • Schwalbe line
  • imaging
  • diagnostic tests/investigation

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  • Funding Grants from the National Medical Research Council and the National Research Foundation, Singapore.

  • Competing interests TYW and TA have received grant funding from Carl Zeiss Meditec, but this was not related to the subject of this study. TA has received travel support and honoraria from Carl Zeiss Meditec.

  • Patient consent Obtained.

  • Ethics approval Ethics approval was provided by the Singapore Eye Research Institute.

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

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