Online optical coherence tomography during subthreshold laser irradiation

PURPOSE. To investigate the role of real-time optical coherence tomography (OCT) in the detection of standard and nonvisible subthreshold laser irradiation. METHODS. We used an integrated platform consisting of a slit-lamp, a digital camera, a slit-lamp mounted OCT, and a 532-nm laser photocoagulator (Topcon Inc., Tokyo, Japan). The laser aiming beam and the OCT scan were aligned to obtain real-time tomographic imaging of the irradiated area during laser exposure. Standard and subthreshold laser irradiation and simultaneous OCT acquisition were tested in artificial and biological samples. Laser testing cards were chosen as artificial samples. Freshly enucleated pig eyes were used for iris irradiation. RESULTS. Ophthalmoscopically visible reference burns were placed on the laser testing card in 2 parallel lines. Then, a series of laser spots with the same size and duration but different power were placed between the reference burns. Online OCT during laser irradiation detected changes in the reflectivity profile of the artificial sample at a power of 200 mW, in absence of ophthalmoscopically visible lesions. Similarly, reference burns were placed on pig iris and between them various laser spots were performed at ranging powers. Changes in the iris optical properties, as detected with online OCT, were produced with a power of 860 mW in absence of visible endpoint. CONCLUSIONS. Online OCT is able to identify non-ophthalmoscopically visible lesions during subthreshold laser irradiation either in artificial samples or in pig iris.