Photocoagulation laser control using phase-sensitive optical coherence tomography toward laser lesion management

Abstract

Purpose : Management of laser lesion requires to control laser fluence due to coagulation laser irradiation. To investigate retinal photocoagulation controlled by phase-sensitive optical coherence tomography (OCT), laser lesions classified by OCT and control parameter are analyzed.

Methods : Eight ex vivo enucleated porcine eyes were involved in the experiment. The 1-μm wavelength OCT system combined with coagulation laser was used. An M-mode OCT scan was acquired at the irradiation point, during the laser irradiation with 400 mW. Depth-localized optical path length (OPL) change and a deformation metric were computed from the phase of OCT signal. The endpoint of the laser irradiation is controlled by the real-time monitoring of the deformation metric. For each eye, laser irradiation with 8 thresholds of the metric (5, 10, 15, 20, 25, 30, 40, 50 μm) were applied. The laser lesions were classified by comparing the OCT volumes before and after the irradiation (Class 0: No change, Class 1: Thickening of the RPE complex, Class 2: Hyper-scattering spot at the outer nuclear layer). The metric thresholds and laser durations were compared to laser lesion classes by ordinal logistic regression analysis.

Results : Figure 1 exemplify a case with 20-μm metric threshold. At each metric threshold, laser lesion classification results (Class 0/Class1/Class 2) are 7/1/0 at 5 μm, 3/4/1 at 10 μm, 1/6/1 at 15 μm, 0/5/3 at 20 μm, 0/3/5 at 25 μm, 0/2/6 at 30 μm, 0/1/7 at 40 μm, and 0/1/7 eyes at 50 μm. Ordinal logistic regression analysis shows that the threshold metric and laser duration are comparable to explain laser lesion classification. This suggests that the deformation metric will be a suitable additional laser control parameter when irradiation condition is varying due to uncontrollable factors such as opacity of anterior part, and pigmentation.

Conclusions : Real-time retinal photocoagulation control by tissue deformation monitoring using OCT will be suitable to manage laser lesion.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.

 

Cross-sectional images of one porcine eye with 20 μm threshold metric level. OCT cross sections (Left) before and (Right) after the laser irradiation. (Middle) M-mode OCT and local OPL change rate. The yellow ticks indicate the expected laser irradiation location. The laser irradiation stopped around 23 ms (white arrow in the middle pane). The slight elevation of the RPE complex appeared (white arrow in right pane).