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the ability of the eye to focus on both near and distant objects, by adjusting its focal length, is called the accommodation of the eye.
the smallest distance, at which the eye can see objects clearly without strain, is called the near point of the eye or the least distance of distinct vision. for a young adult with normal vision, it is about 25 cm.
the common refractive defects of vision include myopia, hypermetropia and presbyopia. myopia (short-sightedness – the image of distant objects is focused before the retina) is corrected by using a concave lens of suitable power.
hypermetropia (far-sightedness – the image of nearby objects is focused beyond the retina) is corrected by using a convex lens of suitable power. the eye loses its power of accommodation at old age.
the splitting of white light into its component colours is called dispersion.
scattering of light causes the blue colour of sky and the reddening of the sun at sunrise and sunset.