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Changes in anterior segment morphology in response to illumination and after laser iridotomy in Asian eyes: an anterior segment OCT study
  1. Jovina L S See1,
  2. Paul T K Chew1,5,
  3. Scott D Smith3,
  4. Winifred P Nolan4,
  5. Yiong-Huak Chan5,
  6. David Huang8,
  7. Ce Zheng5,
  8. Paul J Foster4,6,
  9. Tin Aung1,5,7,
  10. David S Friedman2
  1. 1
    National University Hospital, Singapore
  2. 2
    Wilmer Eye Institute and Johns Hopkins Bloomberg School of Public Health, Baltimore, USA
  3. 3
    Cole Eye Institute, Cleveland, USA
  4. 4
    Institute of Ophthalmology, London, UK
  5. 5
    National University of Singapore
  6. 6
    Moorfields Eye Hospital, London, UK
  7. 7
    Singapore National Eye Centre, Singapore
  8. 8
    Doheny Eye Institute, Los Angeles, USA
  1. David S Friedman, 600 North Wolfe Street, Wilmer 120, Johns Hopkins Hospital, Baltimore, MD 21287, USA; David.friedman{at}


Aim: Using the anterior segment optical coherence tomography (AS-OCT) to quantify changes in anterior segment morphology going from light to dark and following laser iridotomy (LI).

Methods: Prospective observational study. 17 consecutive subjects without peripheral anterior synechiae undergoing LI were evaluated using gonioscopy and AS-OCT. Angle configuration including angle opening distance (AOD) at 500 microns anterior to the scleral spur, AOD500, trabecular-iris space area up to 750 microns from the scleral spur, TISA750 and the increase in angle opening going from dark to light conditions was determined.

Results: Both mean AOD500 and TISA750 increased nearly threefold going from dark to light. Both also significantly increased following LI (p<0.001) as did gonioscopic grading of the angle in all quadrants (p<0.001, McNemar’s test). Angles were more than twice as wide on average in the dark after LI than before LI (p<0.05). Both the mean absolute change and the mean proportionate change in AOD500 and TISA750 when going from light to dark were greater after LI than before (p<0.05).

Conclusion: Increased illumination as well as LI resulted in significant widening of the anterior chamber angle. AS-OCT (which does not require a water bath and can be performed with the patient at the slit lamp) identified similar magnitude changes as those previously reported using ultrasound biomicroscopy (UBM). Furthermore, the angle appears to open more both in absolute terms and and proportionate terms in response to illumination after LI.

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  • SDS and TA have received financial support for travel to conferences from Carl Zeiss Meditec. DSF has previously been a consultant to Carl Zeiss Meditec. DH receives patent royalty and research grant from Carl Zeiss Meditec.

  • Funding: Carl Zeiss Meditec loaned the anterior segment OCT for the study and provided technical support.

  • Abbreviations:

    angle opening distance


    anterior segment optical coherence tomography


    intraocular pressure


    laser iridotomy


    primary angle-closure glaucoma


    ultrasound biomicroscopy