Integrative advances for OCT-guided ophthalmic surgery and intraoperative OCT: microscope integration, surgical instrumentation, and heads-up display surgeon feedback

Abstract

Purpose: To demonstrate key integrative advances in microscope-integrated intraoperative optical coherence tomography (iOCT) technology that will facilitate adoption and utilization during ophthalmic surgery.

Methods: We developed a second-generation prototype microscope-integrated iOCT system that interfaces directly with a standard ophthalmic surgical microscope. Novel features for improved design and functionality included improved profile and ergonomics, as well as a tunable lens system for optimized image quality and heads-up display (HUD) system for surgeon feedback. Novel material testing was performed for potential suitability for OCT-compatible instrumentation based on light scattering and transmission characteristics. Prototype surgical instruments were developed based on material testing and tested using the microscope-integrated iOCT system. Several surgical maneuvers were performed and imaged, and surgical motion visualization was evaluated with a unique scanning and image processing protocol.

Results: High-resolution images were successfully obtained with the microscope-integrated iOCT system with HUD feedback. Six semi-transparent materials were characterized to determine their attenuation coefficients and scatter density with an 830 nm OCT light source. Based on these optical properties, polycarbonate was selected as a material substrate for prototype instrument construction. A surgical pick, retinal forceps, and corneal needle were constructed with semi-transparent materials. Excellent visualization of both the underlying tissues and surgical instrument were achieved on OCT cross-section. Using model eyes, various surgical maneuvers were visualized, including membrane peeling, vessel manipulation, cannulation of the subretinal space, subretinal intraocular foreign body removal, and corneal penetration.

Conclusions: Significant iterative improvements in integrative technology related to iOCT and ophthalmic surgery are demonstrated.

Figure 1. Microscope-integrated intraoperative OCT (iOCT) system.

(A) Color photograph of system (red circle) on Leica 844 microscope. (B) Schematic of iOCT system, including tunable lens and monolithic design. DM, dichroic mirror; f, collimating, objective, scan, tube, and electrically tunable lenses; G, galvanometer scanners; M, fold mirrors.

Figure 2. Optical testing of potential instrument materials.

(A) OCT set-up with single material in place for evaluation of attenuation coefficient and scattering density. (B) Sample set of material cylinders tested for optical properties.

Figure 3. HUD system for intraoperative OCT (iOCT) system.

(A) Ocular feedback with target region for surgeon to area of iOCT FOV. (B) Second ocular feedback system with OCT data displayed adjacent to surgeon's view of the surgical field with OCT display both on axis and perpendicular to instrument. Video S1. (Note: contrast non-uniformity in the iOCT HUD images are a result of capturing video snapshots through the surgical microscope ocular). Scale bar: 200 µm.

Figure 4. OCT-based attenuation coefficient and scattering density of potential instrument materials.

The measured attenuation coefficients (yellow) ranged between 2.16–3.31 mm⁻¹ and scattering densities ranged from 0.13–23.2% (blue). Index of refraction for each material at 830 nm were also measured. Representative OCT cross-sections of each material are shown.

Figure 5. Examples of OCT-compatible instrument prototypes.

(A) B-scan of prototype surgical pick (orange arrow) in the porcine anterior chamber between the endothelium and the anterior lens capsule. (B) B-scan of prototype surgical pick exerting significant downward pressure on the porcine retinal surface. In both frames, excellent visualization of the instrument profile and underlying tissues is achieved. Images show averages of 5 co-registered adjacent B-scans. Scale bar: 200 µm.

Figure 6. Three dimensional reconstruction of OCT-compatible needle (white asterisk) in porcine eye in (A).

(B) Summed voxel projection showing perpendicular OCT scans (white lines) at needle tip. (C) Intraoperative OCT B-scan parallel to needle from (B) revealing excellent visualization of the needle while maintaining optimal clarity of the underlying tissue. The bore of the needle (white asterisk) is visible on the OCT scan. (D) Intraoperative OCT B-scan perpendicular to needle tip from (B) revealing tissue disruption at the needle tip (i.e., retinal hole) with excellent visualization of underlying and surrounding tissues. Video S2. Scale bar: 50 µ.

Figure 7. Three dimensional reconstruction of OCT-compatible surgical pick (white asterisk) in porcine eye in (A).

(B) Summed voxel projection showing perpendicular OCT scans (white lines) at tip of surgical pick. (C, D) Intraoperative OCT B-scan parallel (C) and perpendicular (D) to pick from (B) revealing excellent visualization of the pick tip (white asterisk) while maintaining optimal clarity of the underlying tissue. Video S3. Scale bar: 500 µm.

Figure 8. Three dimensional reconstruction of OCT-compatible needle (white asterisk) in porcine cornea in (A).

(B) Summed voxel projection showing perpendicular OCT scans (white lines) at tip of needle. (C, D) Intraoperative OCT B-scan parallel (C) and perpendicular (D) to needle from (B) revealing visualization of the penetration depth of the needle tip (white asterisk) relative to the corneal endothelium. Video S4. Scale bar: 500 µm.

Figure 9. Dynamic imaging with HUD system of a diamond dusted membrane scraper on the porcine retinal surface.

Each frame shows progressive OCT-motion (below) corresponding to the surgical view with HUD of OCT target (above). Video S1. Scale bar: 200 µm.

Figure 10. Subretinal cannulation and injection in porcine eye.

Cross-sectional images show (A) semitransparent needle tip entering the subretinal space, (B) initial injection volume displacing surrounding tissue, (C) injection into the subretinal space with elevation of the retina. (D) Immediately post-injection, excess fluid and triamcinolone is observed leaking from the injection site (arrow). Video S5. Scale bar: 500 µm.