Intra-operative optical coherence tomography in glaucoma surgery-a systematic review

Abstract

The application of the OCT in clinical ophthalmology has expanded significantly since its introduction more than 20 years ago. There has been recent growing interest in the application of intra-operative optical coherence tomography (iOCT). The iOCT's ability to enhance visualisation and depth appreciation has the potential to be further exploited in glaucoma surgery, especially with the emergence of Minimally Invasive Glaucoma Surgery (MIGS)-to facilitate targeted device placement and fine surgical manoeuvres in the angles, the sub-conjunctival layer and the suprachoroidal space. Hence, this study aims to appraise the current literature on the applications of iOCT in glaucoma surgery. A total of 79 studies were identified following a literature search adhering to PRISMA guidelines. After full text evaluation, 10 studies discussing iOCT use in glaucoma surgery were included. Traditional glaucoma filtering procedures reviewed included trabeculectomy surgery, goniosynechiolysis, bleb needling and glaucoma drainage device implantation. MIGS procedures reviewed included canaloplasty, trabecular aspiration, ab-interno trabectome and the XEN45 gel stent. iOCT use in ophthalmic surgery is becoming increasingly prevalent and has already been applied in various surgeries and procedures in the field of glaucoma. With the greater adoption of MIGS, iOCT may further contribute in facilitating surgical techniques and improving outcomes. While iOCT offers many advantages, there are still limitations to be overcome-iOCT technology continues to evolve to optimise imaging quality and user-experience.

Fig. 1

PRISMA flowchart

Fig. 2

Intra-operative and iOCT images in bleb needling surgery Courtesy of Dada et al. [15]. a Intra-operative clinical photograph presenting a flat vascularised bleb. The corresponding live iOCT imaging—horizontal scan (blue horizontal line) and vertical scan (red vertical line)—of the bleb shows apposition of the conjunctiva and sclera with minimal hyporeflective space, indicating a fibrosed/non-filtering bleb with a 26G needle in situ (white asterisk). b iOCT imaging showing a relatively diffusely raised bleb with multiple hypo-reflective spaces post bleb needling, with 26G needle in situ (white asterisk)

Fig. 3

Intra-operative and iOCT images in canaloplasty surgery Courtesy of Siebelmann et al. [27]. a Imaging through the prepared Descemet window before donning the suture. The cross shows the scanned area. b The vertical OCT scan showing the suture in the Schlemm’s canal (SC), the trabecular meshwork (TMW), the ciliary body (CB), the iris (I), the anterior chamber (AC) and the cornea (Co). The curvature of the chamber angle (red line) is convex. c Microscope image after closing the suture. The cross shows the scanned area. d The configuration of the chamber angle is now concave, with steepening of the angle between the SC and chamber angle

Fig. 4

Intra-operative and iOCT images during trabecular aspiration Courtesy of Heindl et al. [18]. a The aspiration cannula (arrows) is placed within the iridocorneal angle. To maintain intraocular pressure, an irrigation cannula is additionally placed within the anterior chamber (asterisk). The horizontal line demonstrates iOCT scanning direction. b iOCT image of the iridocorneal angle before placement of aspiration cannula. Iris and trabecular meshwork are shadowed by scleral tissue (Co cornea, CA chamber angle, Ir iris). c iOCT image of the aspiration cannula (arrow) within the iridocorneal angle. With a non-parallel scanning direction, the tip of the instrument is difficult to visualise. d Aspiration cannula (white arrows) is placed within the iridocorneal angle of the porcine eye. The long arrow demonstrates the iOCT scanning direction. e iOCT image of the iridocorneal angle before placement of aspiration cannula in porcine eye (Co cornea, CA chamber angle, Ir iris). f iOCT image with placement of aspiration cannula (arrows) within the iridocorneal angle in porcine eye. The relation between the cannula tip to the trabecular meshwork and the iris is clearly visible. However, structures behind the cannula are shadowed by the cannula

Fig. 5

Intra-operative and iOCT images during ab-interno trabeculotomy Courtesy of Heindl et al. [18]. a The trabectome (arrows) is placed within the iridocorneal angle. The horizontal line demonstrates the iOCT scanning direction. b iOCT image of the iridocorneal angle during placement of the trabectome. Trabecular meshwork is shadowed by scleral tissue, but iris is visible (Co cornea, CA chamber angle, Ir iris). c iOCT section of the trabectome (arrows) within the iridocorneal angle. Iris is not visualised due to the shadowing by the trabectome

Fig. 6

Intra-operative images of sub-conjunctival haemorrhage during XEN implantation Courtesy of Leonard W. L. Yip, FRCSEd and Bryan C. H. Ang, FRCOphth, Singapore. a, b Development of sub-conjunctival haemorrhage during XEN implantation obscuring view of emerging stent. c Good visualisation of the XEN gel stent at the beginning of a needling procedure. d Poor visualisation of the XEN gel stent as needling progresses, due to sub-conjunctival haemorrhage and rising of the bleb. e Ab-externo XEN implantation in an eye undergoing open revision after prior XEN implantation, as the previous stent was found not be patent during surgery

Fig. 7

SS-MIOCT demonstrating scleral tunnelling in live 4D (three-dimensional across time) Courtesy of Pasricha et al. [24]. a Scleral tunnelling using a 23-gauge needle (red arrows) advancing from the surface of the sclera under direct visualisation, preventing the creation of peripheral anterior synechiae formation post-operatively (b) Through the scleral into the anterior chamber. c Through to the deepest point in the anterior chamber, creating a scleral tunnel for subsequent tube shunt placement. d, e Tube shunt (red arrows) insertion through the previously established scleral tunnel into the anterior chamber, with proper positioning anterior to the iris and without corneal touch (SS-MIOCT three-dimensional volume (D) with a white box demarcating its corresponding two-dimensional B-scan (E)). f, g Scleral flap interface (green arrows), sclerotomy (blue arrow), and iridectomy (yellow asterisk) at the end of the trabeculectomy surgery (SS-MIOCT three-dimensional volume (F) with a white box demarcating its corresponding two-dimensional B-scan (G))