Abstract
Abstract: :
Purpose: To investigate the effect of infrared (IR)-radiation, used for stimulation of subretinal silicon microphotodiode arrays, on retinal function in relation to previous reports that demonstrated sensitivity to infrared light-emitting diodes (IREDs, Chow et al. 2001). IR-light is used to stimulate subretinal microphotodiode arrays (MPDAs) and it has to be ensured that retinal photoreceptors are not responding in experimental animals. Method: By means of a modified fundus camera, monochromatic light originating from two different diode lasers (670 nm and 830 nm) was diffusely projected onto the central fundus of two cats (spot size and position can be controlled by the set-up). Laser power ranged from 0.4 to 0.0004 mW at 670 nm (neutral filter density: D 0, 0.3, 0.7, 1, 1.7, 3) and was 23 mW at 830 nm. ERGs were recorded from two cats by standard procedures (pulse length=10 ms, 0.8 Hz), both after dark adaptation of 30 minutes and light adaptation of 15 minutes. For comparison with previous studies (see above) 4 high-energy IREDs were used (875 nm, half bandwidth=37 nm, 150-300 mW/sr, equal conditions). Results: Dark adapted eyes: 670 nm Laser: b-wave amplitude was 117, 74, 49, 30, 11, 0.9 µV for increasing filter strength, resp.; latency was 106-109 ms. IREDs: b-wave amplitude 2.5 µV, latency 72 ms; IR-laser: not detectable (n.d.) a- or b-wave (<0.4 µV). Light adapted eyes: 670 nm Laser: b-wave amplitude was 12, 9.2, 3.8, 2.9 µV, n.d., n.d. for increasing filter strength, resp.; latency was 60-75 ms. IREDs: not detectable a- or b-wave; IR-laser: not detectable a- or b-wave. Conclusion: Monochromatic Laser light at 830 nm did not produce any ERG response, neither after dark nor light adaptation. Minimal sensitivity was detected for IREDs only after dark-adaptation but not in the light-adapted state. A possible reason is the high energy of IREDs and their broad half bandwidth which produces a clearly visible flash. Previous studies used IREDs which might also have produced a peak in the visible range. The design of the fundus camera with the IR Laser is thus usable for selective stimulation of subretinal implants.
Keywords: 554 retina • 316 animal model • 454 laser