Acute ocular hypertension during ophthalmic surgery may lead to decreased retinal blood perfusion, nerve cell damage, and serious postoperative complications. Thus, in depth intraoperative blood perception is required, which standard surgical microscopes supply limitedly. Fluorescein angiography (FA), a traditional method for evaluating retinal blood flow, necessitates injecting fluorescent markers into the subject, which can be time consuming, invasive, and cause various side effects. Optical coherence tomography angiography (OCTA), as a functional extension of optical coherence tomography (OCT), provides a noninvasive, capillary level, and unmarked three-dimensional (3D) blood perfusion using flowing red blood cells (RBCs) as intrinsic agents. Recent developments in high-speed OCT systems and efficient OCTA algorithms promote the clinical practice of OCTA. Here, several microscope-integrated OCT/OCTA systems have been reported, which suggest that iOCT can improve the quality of posterior and anterior segment surgery. However, directly applying the current design to the commercial surgical microscope is difficult because of the interference with surgical ergonomics, and few studies are available intraoperative angiography because of the low contrast between capillaries and retinal tissue in OCT.

A microscope-integrated intraoperative OCTA (iOCTA) system, based on a commercial surgical microscope (OPMI Lumera 300, Carl Zeiss, Germany), is developed for structural and angiographic imaging. The iOCTA system uses an SLD and a high-speed spectrometer, offering the central wavelength of 850 nm, a full width at half maximum bandwidth of 200 nm, A-scan rate of 120 kHz, range of imaging depth of ~2.6 mm, and axial resolution of ~2.3 μm in air. A simple and reliable adapter is designed to couple the imaging lightpath of the microscope and the OCTA through the assistant microscope port from the side, allowing the OCT and microscope to focus simultaneously. This coupling method maintains the surgical ergonomics design of the surgical microscope and can conveniently upgrade the commercial surgical microscope. A noncontact wide angle observation system is used to achieve fundus imaging. A charge-coupled device (CCD) camera is linked to the surgical microscope to capture images or record videos. The feasibility of the proposed iOCTA system is confirmed by monitoring the blood perfusion of a live rabbit’s eyes during ophthalmic surgery. Acute ocular hypertension during cataract surgery or vitrectomy is simulated by artificially changing the intraocular pressure (IOP) of the rabbit’s eyes. The main stages of the ophthalmic surgery included puncturing the sclera, maintaining IOP at 60 mmHg for 10 min, and recovering IOP to the normal value for 1 h. A series of representative intraoperative angiography of the rabbit’s eyes is obtained in different stages during surgery. With 400 A-scans per B-scan, three repeated B-scans (in the X-direction) per lateral location, and 400 lateral locations (in the Y-direction) per 3D data, an OCTA scan is completed in ~4.8 s. To accurately distinguish dynamic blood flow regions and static surrounding tissues, the inverse signal-to-noise ratio (iSNR)-decorrelation OCTA (ID-OCTA) algorithm is used, where a classification line is set in a 1D space along the 3σ boundary of the distribution of static signals to remove the static tissues. By reconstruction and projection, a two-dimensional en-face image of OCTA containing dynamic signals of the whole 3D data is further achieved. Moreover, quantitative analysis of vessel density is performed to demonstrate longitudinal in-vivo optical imaging of retinal blood during surgery.

Compared with the image captured by the CCD camera of the surgical microscope, high-resolution iOCTA obtained by the iOCTA system not only visualizes more capillary details but also improves the contrast of imaging at the capillary level (Fig. 2). The en-face images of OCTA in Fig. 3 reveal that retinal capillary filling is extinguished, and the diameter of the big vessels reduce within the peak IOP (60 mmHg). Capillary filling and the diameter of the big vessels recover within 3 min after the intraocular pressure acutely decreases to the initial value. The vessel density trend in Fig. 4 reveals that the retinal vessel density decreases significantly (reduced to below 20% of the baseline) within 1 min when the IOP increases acutely during surgery, decreases mildly within 10 min of maintaining peak IOP (60 mmHg), and rapidly rises to the initial vessel density within 2 min when the IOP returns to normal. En-face images of OCTA and the trend of vessel density demonstrate the negative correlation between blood perfusion and the value of IOP.

This work presents an iOCTA system based on a commercial surgical microscope, which provides the dynamic monitoring of intraoperative retinal blood perfusion. High-resolution intraoperative blood perfusion imaging of a live rabbit’s eyes is acquired using this iOCTA system during ophthalmic surgery. A series of representative en-face images of iOCTA and the trend of vessel density reveal the spatiotemporal dynamic evolution of blood perfusion. Real-time monitoring of retinal blood perfusion during ophthalmic surgery is expected to be realized using this iOCTA system, which will help surgeons objectively evaluate the surgical procedures and predict postoperative effects.