Results
Pulsed Ultraviolet Radiation at 355 nm Short and Long Exposures
Six lenses from donors aged 54 to 72 years were irradiated at 355 nm and were found to develop white lesions instantaneously at a mean laser irradiance of 65 mW/cm (corresponding to a pulse energy of 0.4 μJ) or higher, Figure 1. White lesions were avoided when laser irradiance was reduced to 16 mW/cm2 (corresponding to a pulse energy of 0.1 μJ) but prolonged exposure (~72 hours) led to brown lesions, Figure 1. In all 6 lenses transmission at 355 nm was < 1% before exposure. No light transmission was detectable through the white or brown lesions. In a single case a dose-dependent photobleaching was observed at a laser irradiance of 75 mW/cm that produced photodamage in all other lenses, see Figure 2. In this single case of photobleaching, a dose-dependent increase in transmission of short wavelengths was noted with a maximum effect around 410 nm.
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Figure 1.
Photowhitening and photodarkening. Close-up photographs showing the white (left) and brown (right) lesions produced by irradiation with a 355 nm pulsed laser. The lesions are circular with a diameter of 1.4 mm, corresponding to the aperture used.
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Figure 2.
Transmission changes after 355 nm. Changes in transmission after irradiation of a 72 year old human donor lens with a 355 nm pulsed laser. Each graph represents a 60 minute exposure duration. This was the only lens that showed a dose-response photobleaching after exposure to 355 nm.
Pulsed and Continuous Wave Violet Light at 400 and 405 nm Short, Intermediate and Long Exposures
The effects of pulsed and continuous wave (cw) lasers were compared using a cw (405 nm) and a femtosecond pulsed laser (400 nm). Seven lenses from donors aged 64 to 73 years were irradiated with the pulsed laser and 7 lenses from donors aged 57 to 75 years were irradiated with the cw system. Light transmission before exposure was on average 1.1% at 400 nm and it was 2.2% at 405 nm. Using the pulsed laser system, white lesions were produced instantaneously with pulse energy densities < 0.4 μJ/cm or higher. No light transmission was detectable through the white lesions. Lower laser irradiances resulted in macroscopically visible photobleaching and increased transmission of predominantly blue light, Figure 3. Blue light transmission from 450–490 nm increased by 4.7 - 18.8% after irradiation. A similar result was obtained for the cw irradiation with production of white lesions at laser irradiances < 165 mW/cm while lower irradiances led to photobleaching. Blue light transmission from 450–490 nm increased by 9.7 to 34.2% after irradiation. Brown lesions were not observed after irradiation with the violet lasers (exposure durations up to 18 hours).
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Figure 3.
Transmission changes after 400 nm. Changes in transmission as a function of wavelength after irradiation of a 64 year old human donor lens with a 400 nm femtosecond pulsed laser for 18 h 47 minutes and 23 h and 28 minutes. The transmission before irradiation was set to 100% for all wavelengths.
Continuous Wave Green Light at 532 nm Short and Intermediate Exposures
All three lenses (aged 68 to 72 years) irradiated with a green cw laser had a light transmission at 532 nm of 57- 84% before irradiation and they consistently showed a minor increase in transmission of 8.0 - 8.3% in the blue region from 450–490 nm after irradiation by ~1.6 kJ/cm, Figure 4. The effects were barely visible macroscopically. Increasing the radiation dose up to 105 minutes (~3 kJ/cm) did not result in further photobleaching or formation of white or brown lesions.
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Figure 4.
Transmission changes after 532 nm. Changes in transmission of a human donor lens (aged 72 years) during irradiance with a 532 nm continuous wave laser for 10 and 40 minutes. Transmission before irradiation was set to 100% for all wavelengths.