Investigation of the Influence of Pulse Duration and Application Mode on Microsecond Laser Microsurgery of the Retinal Pigment Epithelium

Abstract

Optical microsurgery confined to the retinal pigment epithelium (RPE) requires locally optimized laser parameters and reliable real-time feedback dosimetry (RFD) to prevent unwanted neuroretinal overexposure. This study aimed to compare pulses of different durations and application modes (single, ramp, burst). Moreover, optical coherence tomography (OCT)-based RFD was investigated in an ex vivo experiment, utilizing nine porcine eyes that were exposed to laser pulses of 8, 12, 16 and 20 µs duration (wavelength: 532 nm, exposure area: 90 × 90 µm2, radiant exposure: 247 to 1975 mJ/µm2). Simultaneously, time-resolved OCT M-scans were recorded (central wavelength: 870 nm, scan rate: 85 kHz) for RFD. Post irradiation, retinal changes were assessed with color fundus photography (CFP) and cross-sectional OCT B-scans. RPE cell damage was quantified via fluorescence-based cell viability assay and compared to the OCT dosimetry feedback. Our experiments indicate cumulative RPE damage for pulse bursts of 16 µs and 20 µs, whereas no cumulative effects were found for pulse durations of 8 µs and 12 µs applied in ramp mode. According to statistical analysis, OCT-RFD correctly detected RPE cell damage with 96% sensitivity and 97% specificity using pulses of 8 µs duration in ramp mode.

Real-time OCT feedback-controlled RPE photodisruption in ex vivo porcine eyes using 8 microsecond laser pulses

“…These results suggest that, as intended for SRT, using pulse bursts and a relatively low repetition rate of 100 Hz at pulse durations shorter than the theory-derived thermal relaxation time for RPE cells (10 µs) [15], there are no cumulative thermal effects in the tissue whilst only high peak temperatures appear trigger MBF and RPE damage. This also corresponds to our latest ex vivo porcine eye experiment where cumulative RPE damage could be excluded for pulse durations of 8 and 12 µs applied in ramp-mode [63].…”

“…As already mentioned in our latest publication [63], a limitation of our ex vivo porcine eye experiments can of course be related to the ex vivo experimental setting. Although the eyes were treated as soon as possible after enucleation, the intraocular pressure was maintained and the cornea was moistened, the thermodynamic processes may have been different from an in vivo situation.…”

Real-time OCT feedback-controlled RPE photodisruption in ex vivo porcine eyes using 8 microsecond laser pulses

“…These results suggest that, as intended for SRT, using pulse bursts and a relatively low repetition rate of 100 Hz at pulse durations shorter than the theory-derived thermal relaxation time for RPE cells (10 µs) [ 15 ], there are no cumulative thermal effects in the tissue whilst only high peak temperatures appear trigger MBF and RPE damage. This also corresponds to our latest ex vivo porcine eye experiment where cumulative RPE damage could be excluded for pulse durations of 8 and 12 µs applied in ramp-mode [ 76 ].…”

“…As already mentioned in our latest publication [ 76 ], a limitation of our ex vivo porcine eye experiments can of course be related to the ex vivo experimental setting. Although the eyes were treated as soon as possible after enucleation, the intraocular pressure was maintained and the cornea was moistened, the thermodynamic processes may have been different from an in vivo situation.…”