By the time we hit our 40's many of us will suffer one of these two extremes and have to wear glasses either for reading or for driving or, in my case, for both. In old age shortsightedness is caused by the lens loosing its elasticity and remaining squeezed, and longsightedness by it losing flexibility and the cillary muscle losing strength so that the lens cannot be squeezed as much. The lens in the eye focuses this expanding cone back into a contracting one that comes to a point on the retina corresponding to the position of the pixel "out there on the screen".įocusing is achieved by a muscle around the eye's flexible lens, the cillary muscle, which squeezes the lens into a more spherical shape to cause rays entering the eye to bend more, brings no objects closer to the eye into focus, or by the cillary muscle relaxing, allowing the lens to stretch back to a flatter shape, to bend rays less, bringing objects further away into focus. You can visualize the light from a point (say a pixel) that reaches the iris as a cone. When the iris is dilated (open) the eye allows as much light as possible into it. The iris in the eye expands or contracts to allow or restrict the amount of light entering the eye, attempting to maintain a constant luminosity on the retina so that either not too little, or not too much light falls on the cones and rods in the retina. Hi Dark Themers, in an earlier life I worked in optics, designing holographic cameras for bubble chamber physics, so I know a little about focussing systems and depth of field.
A while back, Eliot Miranda posted a detailed message for dark theme users on the squeak-dev mailing list.
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