How does the yellowing of the lens with age affect: colour vision, scotopic vision and the contrast of tests charts that are spectrally neutral?
In general as the lens ages it becomes more yellow and also scatters more light. It also hardens such that we can no longer accommodate to near viewing distances and have to wear reading glasses. The yellowing is caused by absorption and scattering. To answer your questions. (a) Color vision is not affected as much as we might think because our visual systems adapt to the yellowing and the world still appears fairly normal (it doesn’t take on a yellow cast). However, certain colors will be influenced more than others. Blues will look darker and purple colors will look more like reds. The main effect is that colors that matched when we were young might no longer match as we age. This is just like what happens if we put on yellow sun glasses and looked at various color matches. (b) For scotopic vision, there is less light that the rods are sensitive to in the blue region of the spectrum. This results in a decrease in scotopic sensitivity. In other words, it gets harder to see at night. T
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