Tissue response of selective retina therapy by means of a feedback-controlled energy ramping mode

Background: The purpose of the study was to evaluate the safety and selectivity of the retinal pigment epithelium lesions by using automatic energy ramping and dosimetry technique for selective retina therapy and to investigate the healing response. Methods: Ten eyes of Chinchilla Bastard rabbits were treated with an automatic dosage controlled selective retina therapy laser (frequency doubled Q-switched Nd:YLF, wavelength: 527nm, pulse duration: 1.7μs, repetition rate: 100Hz, pulse energy: linear increasing from pulse to pulse up to shut down - maximal 110μJ, max. number of pulses in a burst: 30, retinal spot diameter: 133μm). After treatment, fundus photography, optical coherence tomography and fluorescein angiography were performed at three time points from 1h to 3 weeks. Histological analysis was performed. Results: A total of 381 selective retina therapy laser spots were tested (range 13-104μJ).Typical fundus photographs obtained at 1h after irradiation showed that 379 out of 381 lesions produced by selective retina therapy were not visible ophthalmoscopically and the lesions could be detected by angiography only. Optical coherence tomography images revealed that the structure of photoreceptors was preserved, but a disrupted retinal pigment epithelium layer was observed as was expected. By 3 weeks, histology showed selective retinal pigment epithelium damage without any effect on the inner retina and focal proliferation of the retinal pigment epithelium layer. Conclusions: Automatically controlled selective retina therapy is a significant improvement in this innovative treatment. It could be demonstrated that the non-contact, reflectometric technique with a controlled pulse energy ramp is safe and selective.