Blue light dose distribution and retinitis pigmentosa visual field defects: an hypothesis

The hypothesis that retinitis pigmentosa (RP) is worsened by blue light has been raised a century ago. In order to check this hypothesis we calculated the theoretical dose distribution of light on the retinal surface. The relative dose to the different parts of the retina was calculated using a Monte-Carlo method. The changes in the peripheral isopters were calculated both degrading at a constant rate and degrading proportionally to light exposure. There is a considerably greater exposure to the superior compared to the inferior visual field. The maximum dose of UV and blue light is located on the superior field about 4mm above the macula. The dose received by the peripheral retina is markedly lower than the dose received by the central retina. The visual field defects most commonly described in RP are concentric, centered by the macula. These defects cannot, therefore, be explained by the impact of light on the retina. But some regional form of RP with a superior field defect can result from an abnormal genetically encoded sensitivity to ultraviolet and blue light.