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Inverted Ångström sign on iOCT: cannulated Schlemm’s canal during gonioscopy-assisted transluminal trabeculotomy
  1. Karthikeyan Mahalingam,
  2. Viney Gupta and
  3. Shikha Gupta
  1. Glaucoma services, Dr Rajendra Prasad Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi, Delhi, India
  1. Correspondence to Dr Shikha Gupta; dr.shikhagupta84{at}

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We describe a novel method to identify the position of the suture in the Schlemm’s canal during gonioscopy-assisted transluminal trabeculotomy (GATT). A patient with primary angle-closure glaucoma had right eye (RE) cataract and total glaucomatous optic neuropathy. RE vision was 5/60, and intraocular pressure (IOP) was 28 mm Hg on maximum glaucoma medications. RE phacoemulsification with 360° GATT using burnt tip 6–0 prolene suture was performed. Intraoperatively, the pigmented trabecular meshwork (TM) precluded correct identification as the suture was advanced (figure 1A, red arrow). To assist in confirmation of the correct suture positioning and advancement within the Schlemm’s canal, Swan Jacob lens-aided intraoperative-Optical Coherence Tomography (iOCT, OPMI LUMERA-700, Carl Zeiss Meditec, Germany) was used. The suture was seen as an inverted Ångström (Å) sign within the Schlemm’s canal (figure 1B, white arrow). Iris and cornea are considered as two arms of Å and the suture as the circle at their junction. At 1-month follow-up, vision improved to 6/9, and IOP was 12 mm Hg on two topical glaucoma medications.

Figure 1

(A) Intraoperative gonioscopic image showing the advancement of 6–0 prolene suture. Red arrow shows pigmented trabecular meshwork obscuring the suture. (B) Intraoperative-OCT aids in identifying suture (white arrow) as an inverted Ångström sign.

Conjunctiva sparing, angle-based, minimally invasive glaucoma surgeries gained importance in recent years due to the complications faced in the gold standard trabeculectomy.1 2 GATT is one of the minimally invasive, ab interno surgeries which can treat up to 360° of anterior chamber angle in both open-angle and angle-closure glaucoma.3 4 As it is a recently introduced procedure requiring gonioscopy-assisted angle visualisation, there can be a significant initial learning curve.1 5 Added to it, the advancement of the suture in the Schelmm’s canal cannot be seen through gonioscopy due to the overlying pigmented TM. To overcome this difficulty, iOCT can be used to confirm the position of the suture. Subsequent to this case, the inverted Å sign was found to be replicable and reliable sign in all the future GATT surgeries performed with the aid of iOCT. iOCT can provide 360° view of anterior chamber angle, helping in preventing suture misdirection in eyes with pigmented TM.

Patient’s perspective

I am happy that my surgery was completed successfully without complications and I thank the doctor for the same.

Learning points

  • Pigmented trabecular meshwork can hinder the correct identification of suture during gonioscopy-assisted transluminal trabeculotomy.

  • Intraoperative-OCT can help in identifying the position of the suture during the surgery.

Ethics statements

Patient consent for publication



  • Contributors KM, VG and SG contributed equally to conception and design, acquisition of data, drafting the article, revising it critically for important intellectual content and final approval.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Case reports provide a valuable learning resource for the scientific community and can indicate areas of interest for future research. They should not be used in isolation to guide treatment choices or public health policy.

  • Competing interests None declared.

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