Detection of intracellular cavitation during selective targeting of the retinal pigment epithelium with a laser scanner

Certain retinal diseases, such as diabetic macular edema and drusen in age-related macular degeneration, are associated with a dysfunction of the retinal pigment epithelium (RPE), a post-mitotic cell layer crucial for the metabolism in the outer retina. Current therapies can manage disease complications but do not address the RPE's pivotal role in the early pathogenesis. Selective retina therapy (SRT) aims to selectively damage RPE in order to stimulate generation of healthy cells that may be able to remove existing edema or drusen.;This thesis addresses two outstanding challenges in SRT. First, the complicated SRT lasers are difficult to implement in clinics. Second, selective lesions are invisible in slit-lamp examination; a feedback mechanism is needed to ensure successful yet safe treatment. We hypothesized that RPE cells can be selectively destroyed by scanning the beam of a continuous-wave laser rapidly across the retina to produce microsecond-exposures at each irradiated RPE cell. In order to develop an online monitoring system, a solid understanding of the cell damage mechanism is crucial.;Successive generations of scanners were developed around an acousto-optic scanning platform, first for testing the feasibility of selectively destroying RPE cells ex-vivo on explants of bovine RPE, followed by in-vivo demonstration in rabbits over a wide range of clinically crucial exposure durations. Additional modules were implemented to monitor the backscattering of the treatment laser beam, aiming to detect intracellular cavitation in order to elucidate the cell damage mechanism.;Selective RPE cell damage was achieved with moderate laser power (≈100mW) with a large safety margin. Cavitation was detected routinely as a transient increase in backscattering and accompanied cell death for exposures of up to 10micros.;A compact laser scanner is a promising alternative to SRT and laser photocoagulation. Optical detection of intracellular cavitation is a highly sensitive method to identify RPE cell damage. The cell damage mechanism gradually transitioned from photo-mechanical to photo-thermal damage starting at 10micros exposures. The unique ability of the laser scanner to (1) adjust the cell damage extent and (2) measure the cell damage threshold locally to tightly control dosimetry are the key advantages of the scanning technology.