Light can affect retina in many ways :
- photothermal mechanisms - exposure to intense flashes of less than 20 microseconds that cause a rise in temperature of at least 10 degrees Celsius ;
- photomechanical mechanisms - exposure to flashes shorter than 5 nanoseconds ;
- photochemical mechanisms - light is absorbed by a chromophore and leads to the formation of an electronically excited state of it, resulting in chemical transformations .
The retina is more susceptible to light induced degeneration at lower wavelengths [2, 8]. The damage degree also depends on intensity and exposure duration. 12 hours a day of more than 500 lux light, more than three consecutive days can affect rat retina . 2 hours exposure to white light of 3000 lux has lead to apoptosis in rats retina .
Sunlight irradiance is about 11 W/cm2 (ranges between 1.5 and 122 W/cm2) and causes damage when exposure time is tens of minutes or even less .
Light induces apoptosis by different mechanisms:
Intense light triggers cell death in cones and rods by two distinct mechanisms: rapid, necrosis-like cell death occurs in cones; prolonged, apoptotic death is displayed by rods. However, the areas of cone and rod loss coincide, suggesting some interrelationship .
Cones and rods have different vulnerability .
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