The human eye: is the most valuable and sensitive sense organ and it is a natural optical instrument. The important parts of the eye: Cornea, Iris, Pupil, Eye Lens, Retina.
Power of Accommodation: The ability of the eye to focus objects lying at different distances is called the power of accommodation of the eye.
Least Distance of Distinct Vision Near point: Near point or least distance of distinct vision is the point nearest to the eye at which an object is visible distinctly
The far point of the eye:
Far point of the eye is the maximum distance up to which the normal eye can see things clearly. It is infinity for a normal eye.
The twinkling of a star is due to atmospheric refraction of starlight.
Scattering of light:
When a beam of light falls on an atom, it causes the electron in the atom to vibrate. The vibrating electrons, in turn, re-emit light in all directions. This process is called scattering.

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