The intraoperative use of OCT imaging is currently an area of intense development and will certainly be an important tool for posterior and anterior segment surgeries in the near future. Limitations of current systems will need to be addressed before these systems will allow seamless imaging.
Visualization of retinal manipulation has been limited by the reflectivity and backshadowing of current instrumentation. Ehlers et al. reported improved but still limited visualization of underlying structures with polyamide and silicone tips compared with metallic tips.48
Characterization of the reflectivity and shadowing characteristics of different instruments and various materials will need to be refined to optimize OCT visibility of underlying structures. Development of forceps and other instruments with polyamide or silicone tips may be useful, and identification of novel instrument materials may further improve visibility.
Image quality can be improved by increasing strength of the light source with minimization of signal loss through the extended optical systems, but light source intensity must be carefully limited to minimize risk of possible light-induced toxicities. Currently, the most conservative ANSI requirements limit maximum exposure to less than 700 μW of continuous-wave power in the 800- to 900-nm spectral range through a 7-mm pupil aperture for continuous exposure of up to 8 hours.45–47
Real-time application of intrasurgical OCT systems must also consider additional light from the microscope or from fiberoptic endoillumination during vitreoretinal surgery. The impact of concurrent use of indocyanine green dye or other potentially phototoxic adjuvants will also need to be considered. OCT systems will need to maximize efficiency of their optical pathways while maintaining light exposure within safe limits. Contrast agents optimized for OCT imaging are being developed and may further improve visibility of ocular structures.56
Feedback systems for the surgeon must be optimized and integrated into the surgeon’s control. Current intraoperative OCT prototypes typically require an assistant to operate the OCT driving software and to perform manual, often time-consuming adjustments of the reference arm length. As these units are inevitably refined for commercial use, adjustments of the OCT scanner should be able to be performed by the surgeon, possibly through the use of additional foot-pedals or switches easily accessible to the surgeon.
Additionally, visualization options of the OCT images must be optimized. The data output of current OCT systems is voluminous and cannot be realistically processed instantaneously during surgical maneuvers. The development of tracking software to identify the location of instrument tips will likely prove useful in limiting OCT imaging to the area of interest. It will also be critical to identify information that is important for the surgeon in real time and to develop informatic display options for the surgeon. Currently, volume renderings and summed voxel projections can provide detailed spatial information, but real-time visualization is limited by the cumbersome and time-consuming software processing required to produce these images. Individual B-scans provide cross-sectional information but lack spatial information. The development of faster OCT technology, possibly using swept-source OCT, and of faster software processing algorithms may improve imaging and post-processing speed, which will be important in enabling real-time visualization of three-dimensional OCT renderings.
Display systems will also need to be developed that allow the surgeon to view OCT images in real-time during surgical maneuvers. Current systems typically involve a display monitor on a separate OCT workstation that is not visible to the surgeon without directing attention away from the surgical microscope. A heads-up display that integrates visualization of OCT images into the optical viewports of the surgical microscope may prove useful in safely and simultaneously displaying real-time cross-sectional OCT imaging with direct viewing of ocular structures.
A novel approach to intraoperative visualization of OCT images is the prototype OCT Penlight,57
which uses a half-silvered mirror to project an in situ virtual image of a real-time OCT scan within the surgeon’s line of sight. Testing of the OCT Penlight in ophthalmic surgical procedures has not been reported, but this innovative approach may prove useful, particularly for real-time visualization of anterior segment structures.