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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 LS See,
  2. Paul TK Chew,
  3. Scott D Smith,
  4. Winifred P Nolan,
  5. Yiong-Huak Chan,
  6. David Huang,
  7. Ce Zheng,
  8. Paul J Foster,
  9. Tin Aung,
  10. David S Friedman (dfriedma{at}
  1. National University Hospital, Singapore
  2. National University of Singapore, Singapore
  3. Cole Eye Institute, United States
  4. Institute of Ophthalmology, United Kingdom
  5. National University of Singapore, Singapore
  6. Doheny Eye Institute, United States
  7. National University of Singapore, Singapore
  8. Moorfields Eye Hospital, United Kingdom
  9. Singapore National Eye Centre, Singapore
  10. Wilmer Eye Institute and Johns Hopkins Bloomberg School of Public Health, United States


    Background/Aim: To quantify changes in anterior segment morphology going from light to dark and following laser iridotomy (LI).

    Methods: Prospective observational study. 27 consecutive subjects undergoing LI were evaluated using gonioscopy and anterior segment optical coherence tomography (AS-OCT). Angle configuration including angle opening distance 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 three-fold going from dark to light. Both also significantly increased following LI (p<0.002) as did gonioscopic grading of the angle in the nasal and temporal 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). Interestingly, while the mean absolute change in AOD500 and TISA500 when going from light to dark was greater after LI than before (p < 0.05), the mean proportionate change was not.

    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 UBM. Furthermore, while the angle appears to open somewhat more after LI in absolute terms in response to illumination, the proportionate change appears similar before and after LI.

    • Anterior segment OCT
    • illumination
    • laser iridotomy

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