INTRA-OP IMAGE

4D imaging’ that integrates swept-source optical coherence tomography (OCT) in the surgical microscope to provide real-time volumetric visualisation has exciting potential as a clinical and teaching tool for ophthalmic surgery, reported Neel Pasricha at the 2015 annual meeting of the Association for Research in Vision and Ophthalmology in Denver, USA.

“Currently used ophthalmic surgical microscopes can only provide an en face view of the surgical field and so the visual depth needs to be inferred. As OCT provides direct depth information, its integration with the microscope allows for simultaneous dynamic imaging and surgery,” explained Mr Pasricha, a medical student at Duke University, Durham, North Carolina, USA. He works with Dr Anthony Kuo in the Duke MI-OCT imaging team led by Dr Cynthia Toth and Dr Joseph Izatt, the co-inventors of this technology.

The OCT system has custom tracking hardware, an A-scan rate of 100kHz with 500 A-scans per B-scan, and a volume rate of 2Hz, which means the information is updated twice per second. In its original iteration, the MI-OCT information was displayed only on a computer monitor.

Now a microscope-integrated stereoscopic heads-up display has been engineered that allows visualisation of the MI-OCT volumes through the surgical binoculars. Presenting intraoperative videos, Mr Pasricha demonstrated use of the 4D system for actively guiding manoeuvres during cataract and cornea transplant surgeries. The dynamic imaging captured creation of a biplanar cataract incision, grooving of the nucleus with the phaco probe, and verification of incision integrity at the end of the procedure during provocative testing.

Steps highlighted during Descemet’s stripping automated endothelial keratoplasty (DSAEK) included the descemetorhexis, graft unfolding, air tamponade, and final checking of the graft interface.

“With the 4D imaging, the surgeon can be confident that the interface is free of bubbles and that there are no peripheral scrolls at the graft edges,” Mr Pasricha said.

4D imaging from a deep anterior lamellar keratoplasty (DALK) case showed how the technology guided accurate positioning of the needle before injecting air to separate Descemet’s membrane and stroma.

The value of 4D imaging as a training tool was investigated in a randomised controlled study evaluating the ability of ophthalmology residents to perform various depth-based anterior segment manoeuvres on porcine eyes. Residents who first performed the steps under direct MI-OCT guidance outperformed controls who trained without that real-time feedback. However, the performance of the controls improved when they operated with the 4D guidance.

The 4D imaging technique is also being developed for use in vitreoretinal surgery, and it has been evaluated during macular hole, retinal detachment and epiretinal membrane procedures.

Neel Pasricha: neel.pasricha@duke.edu