Selective targeting of the retinal pigment epithelium using an acousto-optic laser scanner

Selective targeting of the retinal pigment epithelium (RPE) is a new strategy for treating certain retinal disorders while preserving adjacent photoreceptors. The treatment currently relies on a complex laser system to produce the required microsecond pulse structure. In our new approach, we scan the focus of a continuous-wave (cw) laser beam with acousto-optic deflectors to produce microsecond-long exposures at each RPE cell. Experiments were performed in vitro with a bench-top scanner on samples of young bovine RPE and in vivo on Dutch belted rabbits with a slit-lamp adapted scanner. Effective dose 50% (ED50) for RPE damage was determined in vitro by fluorescence cell viability assay and in vivo by fluorescein angiography. Damage to individual RPE cells was achieved with laser power on the order of 100 mW. Using separated scan lines, we demonstrate selectivity in the form of alternating lines of dead and surviving cells that resemble the scan pattern. Selectivity is also shown by the absence of retinal thermal coagulation in vivo. Selective RPE damage is feasible by rapidly scanning a cw laser beam. The scanning device is an attractive alternative to conventional laser coagulation and pulsed laser targeting of the RPE.